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nlohmann committed 2026-10-26 21:24:35 +00:00
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commit d2e264bd84
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@@ -20,7 +20,7 @@ Add the single header to your project and use the library like this:
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -31,6 +31,10 @@ int main()
j["name"] = "Niels"; j["name"] = "Niels";
j["list"] = {1, 0, 2}; j["list"] = {1, 0, 2};
// read a value into a C++ variable and use it
double pi = j["pi"].get<double>();
std::cout << "2 * pi = " << 2 * pi << '\n';
// serialize with an indent of 4 spaces // serialize with an indent of 4 spaces
std::cout << j.dump(4) << '\n'; std::cout << j.dump(4) << '\n';
} }
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@@ -1 +1 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link rel=icon href=/assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON for Modern C++</title><link rel=stylesheet href=/assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=/assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="/assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=/css/custom.css><script>__md_scope=new URL("/",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=/. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=md-search data-md-component=search role=dialog> <label class=md-search__overlay for=__search></label> <div class=md-search__inner role=search> <form class=md-search__form name=search> <input type=text class=md-search__input name=query aria-label=Search placeholder=SeaLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link rel=icon href=/assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>JSON for Modern C++</title><link rel=stylesheet href=/assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=/assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="/assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=/css/custom.css><script>__md_scope=new URL("/",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=/. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=md-search data-md-component=search role=dialog> <label class=md-search__overlay for=__search></label> <div class=md-search__inner role=search> <form class=md-search__form name=search> <input type=text class=md-search__input name=query aria-label=Search placeholder=SeaLine truncated
+4 -4
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@@ -44,7 +44,7 @@ class (either explicitly or via the conversion operators).
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
namespace ns namespace ns
{ {
@@ -76,7 +76,7 @@ class (either explicitly or via the conversion operators).
auto p = j.get<ns::person>(); auto p = j.get<ns::person>();
std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl; std::cout << p.name << " (" << p.age << ") lives in " << p.address << '\n';
} }
``` ```
@@ -97,7 +97,7 @@ class (either explicitly or via the conversion operators).
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
namespace ns namespace ns
{ {
@@ -145,7 +145,7 @@ class (either explicitly or via the conversion operators).
auto p = j.get<ns::person>(); auto p = j.get<ns::person>();
std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl; std::cout << p.name << " (" << p.age << ") lives in " << p.address << '\n';
} }
``` ```
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@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/from_json/" rel="canonical"><link href=../ rel=prev><link href=../to_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_json - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannadl_serializerfrom_json class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_json </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></sLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/from_json/" rel="canonical"><link href=../ rel=prev><link href=../to_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>from_json - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannadl_serializerfrom_json class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> from_json </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo 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<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>TargetType</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ValueType</span><span class=o>&gt;</span> <span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>TargetType</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>ValueType</span><span class=o>&gt;</span>
<span class=k>static</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>TargetType</span><span class=o>&amp;</span><span class=w> </span><span class=n>val</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span> <span class=k>static</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>from_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>TargetType</span><span class=o>&amp;</span><span class=w> </span><span class=n>val</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span>
<span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>from_json</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>j</span><span class=p>),</span><span class=w> </span><span class=n>val</span><span class=p>)))</span> <span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>from_json</span><span class=p>(</span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>j</span><span class=p>),</span><span class=w> </span><span class=n>val</span><span class=p>)))</span>
@@ -12,7 +12,7 @@
</code></pre></div> <p>This function is usually called by the <a href=../../basic_json/get/ ><code>get()</code></a> function of the <a href=../../basic_json/ >basic_json</a> class (either explicitly or via the conversion operators).</p> <ol> <li>This function is chosen for default-constructible value types.</li> <li>This function is chosen for value types which are not default-constructible.</li> </ol> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>j</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to read from</dd> <dt><code>val</code> (out)</dt> <dd>value to write to</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li>(none) -- the converted value is written to the output parameter <code>val</code>.</li> <li>the <abbr title="JavaScript Object Notation">JSON</abbr> value <code>j</code> converted to <code>TargetType</code></li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) Default-constructible type</summary> <p>The example below shows how a <code>from_json</code> function can be implemented for a user-defined type. This function is called by the <code>adl_serializer</code> when <code>get&lt;ns::person&gt;()</code> is called.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>This function is usually called by the <a href=../../basic_json/get/ ><code>get()</code></a> function of the <a href=../../basic_json/ >basic_json</a> class (either explicitly or via the conversion operators).</p> <ol> <li>This function is chosen for default-constructible value types.</li> <li>This function is chosen for value types which are not default-constructible.</li> </ol> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>j</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to read from</dd> <dt><code>val</code> (out)</dt> <dd>value to write to</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li>(none) -- the converted value is written to the output parameter <code>val</code>.</li> <li>the <abbr title="JavaScript Object Notation">JSON</abbr> value <code>j</code> converted to <code>TargetType</code></li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) Default-constructible type</summary> <p>The example below shows how a <code>from_json</code> function can be implemented for a user-defined type. This function is called by the <code>adl_serializer</code> when <code>get&lt;ns::person&gt;()</code> is called.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span> <span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
<span class=p>{</span> <span class=p>{</span>
@@ -44,13 +44,13 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>p</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>person</span><span class=o>&gt;</span><span class=p>();</span> <span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>p</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>person</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>name</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" ("</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>age</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>") lives in "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>address</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>name</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" ("</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>age</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>") lives in "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>address</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>Ned</span><span class=w> </span><span class=err>Fla</span><span class=kc>n</span><span class=err>ders</span><span class=w> </span><span class=err>(</span><span class=mi>60</span><span class=err>)</span><span class=w> </span><span class=err>lives</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=w> </span><span class=mi>744</span><span class=w> </span><span class=err>Evergree</span><span class=kc>n</span><span class=w> </span><span class=err>Terrace</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>Ned</span><span class=w> </span><span class=err>Fla</span><span class=kc>n</span><span class=err>ders</span><span class=w> </span><span class=err>(</span><span class=mi>60</span><span class=err>)</span><span class=w> </span><span class=err>lives</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=w> </span><span class=mi>744</span><span class=w> </span><span class=err>Evergree</span><span class=kc>n</span><span class=w> </span><span class=err>Terrace</span>
</code></pre></div> </details> <details class=example> <summary>Example: (2) Non-default-constructible type</summary> <p>The example below shows how a <code>from_json</code> is implemented as part of a specialization of the <code>adl_serializer</code> to realize the conversion of a non-default-constructible type.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (2) Non-default-constructible type</summary> <p>The example below shows how a <code>from_json</code> is implemented as part of a specialization of the <code>adl_serializer</code> to realize the conversion of a non-default-constructible type.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span> <span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
<span class=p>{</span> <span class=p>{</span>
@@ -98,7 +98,7 @@
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>p</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>person</span><span class=o>&gt;</span><span class=p>();</span> <span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>p</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>ns</span><span class=o>::</span><span class=n>person</span><span class=o>&gt;</span><span class=p>();</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>name</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" ("</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>age</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>") lives in "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>address</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>name</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>" ("</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>age</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>") lives in "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>p</span><span class=p>.</span><span class=n>address</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>Ned</span><span class=w> </span><span class=err>Fla</span><span class=kc>n</span><span class=err>ders</span><span class=w> </span><span class=err>(</span><span class=mi>60</span><span class=err>)</span><span class=w> </span><span class=err>lives</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=w> </span><span class=mi>744</span><span class=w> </span><span class=err>Evergree</span><span class=kc>n</span><span class=w> </span><span class=err>Terrace</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>Ned</span><span class=w> </span><span class=err>Fla</span><span class=kc>n</span><span class=err>ders</span><span class=w> </span><span class=err>(</span><span class=mi>60</span><span class=err>)</span><span class=w> </span><span class=err>lives</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=w> </span><span class=mi>744</span><span class=w> </span><span class=err>Evergree</span><span class=kc>n</span><span class=w> </span><span class=err>Terrace</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../to_json/ >to_json</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 2.1.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="June 29, 2026 20:15:18 UTC">June 29, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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+4 -4
View File
@@ -40,7 +40,7 @@ The example below shows how a `from_json` function can be implemented for a user
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
namespace ns namespace ns
{ {
@@ -72,7 +72,7 @@ int main()
auto p = j.get<ns::person>(); auto p = j.get<ns::person>();
std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl; std::cout << p.name << " (" << p.age << ") lives in " << p.address << '\n';
} }
``` ```
@@ -90,7 +90,7 @@ The example below shows how a `from_json` is implemented as part of a specializa
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
namespace ns namespace ns
{ {
@@ -138,7 +138,7 @@ int main()
auto p = j.get<ns::person>(); auto p = j.get<ns::person>();
std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl; std::cout << p.name << " (" << p.age << ") lives in " << p.address << '\n';
} }
``` ```
+1 -1
View File
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/" rel="canonical"><link href=../byte_container_with_subtype/subtype/ rel=prev><link href=from_json/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Overview - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new 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6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </lLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/adl_serializer/" rel="canonical"><link href=../byte_container_with_subtype/subtype/ rel=prev><link href=from_json/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>Overview - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../css/custom.css><script>__md_scope=new URL("../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannadl_serializer class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> Overview </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=k>struct</span><span class=w> </span><span class=nc>adl_serializer</span><span class=p>;</span> <span class=k>struct</span><span class=w> </span><span class=nc>adl_serializer</span><span class=p>;</span>
</code></pre></div> <p>Serializer that uses <abbr title="Argument-dependent lookup">ADL</abbr> (<a href="https://en.cppreference.com/w/cpp/language/adl">Argument-Dependent Lookup</a>) to choose <code>to_json</code>/<code>from_json</code> functions from the types' namespaces.</p> <p>It is implemented similarly to</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>ValueType</span><span class=o>&gt;</span> </code></pre></div> <p>Serializer that uses <abbr title="Argument-dependent lookup">ADL</abbr> (<a href="https://en.cppreference.com/w/cpp/language/adl">Argument-Dependent Lookup</a>) to choose <code>to_json</code>/<code>from_json</code> functions from the types' namespaces.</p> <p>It is implemented similarly to</p> <div class=highlight><pre><span></span><code><span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>ValueType</span><span class=o>&gt;</span>
<span class=k>struct</span><span class=w> </span><span class=nc>adl_serializer</span><span class=w> </span><span class=p>{</span> <span class=k>struct</span><span class=w> </span><span class=nc>adl_serializer</span><span class=w> </span><span class=p>{</span>
+2 -2
View File
@@ -28,7 +28,7 @@ This function is usually called by the constructors of the [basic_json](../basic
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
namespace ns namespace ns
{ {
@@ -55,7 +55,7 @@ This function is usually called by the constructors of the [basic_json](../basic
json j = p; json j = p;
std::cout << j << std::endl; std::cout << j << '\n';
} }
``` ```
+3 -3
View File
@@ -1,11 +1,11 @@
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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> to_json </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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<span class=k>static</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>to_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>TargetType</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>val</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span> <span class=k>static</span><span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>to_json</span><span class=p>(</span><span class=n>BasicJsonType</span><span class=o>&amp;</span><span class=w> </span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>TargetType</span><span class=w> </span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>val</span><span class=p>)</span><span class=w> </span><span class=k>noexcept</span><span class=p>(</span>
<span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>to_json</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>TargetType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>val</span><span class=p>))))</span> <span class=w> </span><span class=k>noexcept</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>to_json</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>TargetType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>val</span><span class=p>))))</span>
<span class=o>-&gt;</span><span class=w> </span><span class=k>decltype</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>to_json</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>TargetType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>val</span><span class=p>)),</span><span class=w> </span><span class=kt>void</span><span class=p>())</span> <span class=o>-&gt;</span><span class=w> </span><span class=k>decltype</span><span class=p>(</span><span class=o>::</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>to_json</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>forward</span><span class=o>&lt;</span><span class=n>TargetType</span><span class=o>&gt;</span><span class=p>(</span><span class=n>val</span><span class=p>)),</span><span class=w> </span><span class=kt>void</span><span class=p>())</span>
</code></pre></div> <p>This function is usually called by the constructors of the <a href=../../basic_json/ >basic_json</a> class.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>j</code> (out)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to write to</dd> <dt><code>val</code> (in)</dt> <dd>value to read from</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how a <code>to_json</code> function can be implemented for a user-defined type. This function is called by the <code>adl_serializer</code> when the constructor <code>basic_json(ns::person)</code> is called.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>This function is usually called by the constructors of the <a href=../../basic_json/ >basic_json</a> class.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>j</code> (out)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to write to</dd> <dt><code>val</code> (in)</dt> <dd>value to read from</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how a <code>to_json</code> function can be implemented for a user-defined type. This function is called by the <code>adl_serializer</code> when the constructor <code>basic_json(ns::person)</code> is called.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>namespace</span><span class=w> </span><span class=nn>ns</span> <span class=k>namespace</span><span class=w> </span><span class=nn>ns</span>
<span class=p>{</span> <span class=p>{</span>
@@ -32,7 +32,7 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span> <span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>p</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>{</span><span class=nt>"address"</span><span class=p>:</span><span class=s2>"744 Evergreen Terrace"</span><span class=p>,</span><span class=nt>"age"</span><span class=p>:</span><span class=mi>60</span><span class=p>,</span><span class=nt>"name"</span><span class=p>:</span><span class=s2>"Ned Flanders"</span><span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../from_json/ >from_json</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 2.1.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="November 1, 2023 20:23:55 UTC">November 1, 2023</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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+2 -2
View File
@@ -25,7 +25,7 @@ The example below shows how a `to_json` function can be implemented for a user-d
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
namespace ns namespace ns
{ {
@@ -52,7 +52,7 @@ int main()
json j = p; json j = p;
std::cout << j << std::endl; std::cout << j << '\n';
} }
``` ```
+2 -1
View File
@@ -121,6 +121,7 @@ The class satisfies the following concept requirements:
- [**json_pointer**](../json_pointer/index.md) - JSON Pointer implementation - [**json_pointer**](../json_pointer/index.md) - JSON Pointer implementation
- [**json_serializer**](json_serializer.md) - type of the serializer to for conversions from/to JSON - [**json_serializer**](json_serializer.md) - type of the serializer to for conversions from/to JSON
- [**error_handler_t**](error_handler_t.md) - type to choose behavior on decoding errors - [**error_handler_t**](error_handler_t.md) - type to choose behavior on decoding errors
- [**bjdata_version_t**](bjdata_version_t.md) - type to choose the BJData version to write
- [**cbor_tag_handler_t**](cbor_tag_handler_t.md) - type to choose how to handle CBOR tags - [**cbor_tag_handler_t**](cbor_tag_handler_t.md) - type to choose how to handle CBOR tags
- **initializer_list_t** - type for initializer lists of `basic_json` values - **initializer_list_t** - type for initializer lists of `basic_json` values
- [**input_format_t**](input_format_t.md) - type to choose the format to parse - [**input_format_t**](input_format_t.md) - type to choose the format to parse
@@ -351,7 +352,7 @@ Access to the JSON value
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+5 -5
View File
@@ -111,19 +111,19 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
// a valid JSON text // a valid JSON text
auto valid_text = R"( const auto* valid_text = R"(
{ {
"numbers": [1, 2, 3] "numbers": [1, 2, 3]
} }
)"; )";
// an invalid JSON text // an invalid JSON text
auto invalid_text = R"( const auto* invalid_text = R"(
{ {
"strings": ["extra", "comma", ] "strings": ["extra", "comma", ]
} }
@@ -153,7 +153,7 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
#include <vector> #include <vector>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -184,7 +184,7 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
#include <string> #include <string>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+8 -8
View File
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/accept/" rel="canonical"><link href=../~basic_json/ rel=prev><link href=../array/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>accept - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </labeLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/accept/" rel="canonical"><link href=../~basic_json/ rel=prev><link href=../array/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>accept - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonaccept class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> accept </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>&gt;</span> <span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>InputType</span><span class=o>&gt;</span>
<span class=k>static</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>accept</span><span class=p>(</span><span class=n>InputType</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>i</span><span class=p>,</span> <span class=k>static</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>accept</span><span class=p>(</span><span class=n>InputType</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>i</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_comments</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_comments</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
@@ -9,23 +9,23 @@
<span class=k>static</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>accept</span><span class=p>(</span><span class=n>IteratorType</span><span class=w> </span><span class=n>first</span><span class=p>,</span><span class=w> </span><span class=n>SentinelType</span><span class=w> </span><span class=n>last</span><span class=p>,</span> <span class=k>static</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>accept</span><span class=p>(</span><span class=n>IteratorType</span><span class=w> </span><span class=n>first</span><span class=p>,</span><span class=w> </span><span class=n>SentinelType</span><span class=w> </span><span class=n>last</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_comments</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_comments</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_trailing_commas</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>);</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ignore_trailing_commas</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>);</span>
</code></pre></div> <p>Checks whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>.</p> <ol> <li>Reads from a compatible input.</li> <li> <p>Reads from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)</p> <p>The value_type of the iterator must be an integral type with a size of 1, 2, or 4 bytes, which will be interpreted respectively as <abbr title="Unicode Transformation Format">UTF</abbr>-8, <abbr title="Unicode Transformation Format">UTF</abbr>-16, and <abbr title="Unicode Transformation Format">UTF</abbr>-32. If <code>SentinelType</code> differs from <code>IteratorType</code>, it must be comparable to the iterator type with <code>operator!=</code>.</p> <p>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-16 and <abbr title="Unicode Transformation Format">UTF</abbr>-32 sequences are rejected: a lone surrogate, a high surrogate that is not followed by its low surrogate, and a code point above <code>U+10FFFF</code> all make this function return <code>false</code>.</p> </li> </ol> <p>Unlike the <a href=../parse/ ><code>parse()</code></a> function, this function neither throws an exception in case of invalid <abbr title="JavaScript Object Notation">JSON</abbr> input (i.e., a parse error) nor creates diagnostic information.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>InputType</code></dt> <dd> <p>A compatible input, for instance:</p> <ul> <li>an <code>std::istream</code> object</li> <li>a <code class=highlight><span class=kt>FILE</span></code> pointer (throws if null)</li> <li>a C-style array of characters</li> <li>a pointer to a null-terminated string of single byte characters (throws if null)</li> <li>a <code>std::string</code> or a <code>std::string_view</code> (C++17)</li> <li>a container <code>obj</code> for which <code>begin(obj)</code> and <code>end(obj)</code> produce a valid pair of iterators (as found via <abbr title="Argument-dependent lookup">ADL</abbr> or member functions, with semantics compatible to <code>std::begin</code> and <code>std::end</code>)</li> <li>wide characters (<code>wchar_t</code>, <code>char16_t</code>, <code>char32_t</code>), which are converted to <abbr title="Unicode Transformation Format">UTF</abbr>-8: a wide string object (<code>std::wstring</code>, <code>std::u16string</code>, <code>std::u32string</code>) or an array (e.g. a wide string literal); a pointer to a null-terminated wide string (e.g. <code>std::u16string::c_str()</code>) is not supported</li> </ul> </dd> <dt><code>IteratorType</code></dt> <dd> <p>a compatible iterator type, for instance.</p> <ul> <li>a pair of <code>std::string::iterator</code> or <code>std::vector&lt;std::uint8_t&gt;::iterator</code></li> <li>a pair of pointers such as <code>ptr</code> and <code>ptr + len</code></li> </ul> </dd> <dt><code>SentinelType</code></dt> <dd> <p>defaults to <code>IteratorType</code>; may be a different type comparable to <code>IteratorType</code> via <code>operator!=</code>, for instance.</p> <ul> <li>a custom sentinel type for C++20 ranges</li> <li><code>std::default_sentinel_t</code>, when <code>IteratorType</code> is <code>std::counted_iterator</code></li> </ul> </dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>i</code> (in)</dt> <dd>Input to parse from.</dd> <dt><code>ignore_comments</code> (in)</dt> <dd>whether comments should be ignored and treated like whitespace (<code class=highlight><span class=nb>true</span></code>) or yield a parse error (<code class=highlight><span class=nb>false</span></code>); (optional, <code class=highlight><span class=nb>false</span></code> by default)</dd> <dt><code>ignore_trailing_commas</code> (in)</dt> <dd>whether trailing commas in arrays or objects should be ignored and treated like whitespace (<code class=highlight><span class=nb>true</span></code>) or yield a parse error (<code class=highlight><span class=nb>false</span></code>); (optional, <code class=highlight><span class=nb>false</span></code> by default)</dd> <dt><code>first</code> (in)</dt> <dd>iterator to the start of the character range</dd> <dt><code>last</code> (in)</dt> <dd>iterator to the end of the character range, or a sentinel value that compares equal to the end iterator with <code>operator!=</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title=Line truncated </code></pre></div> <p>Checks whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>.</p> <ol> <li>Reads from a compatible input.</li> <li> <p>Reads from a pair of character iterators, or an iterator and a sentinel of a different type (C++20 ranges support)</p> <p>The value_type of the iterator must be an integral type with a size of 1, 2, or 4 bytes, which will be interpreted respectively as <abbr title="Unicode Transformation Format">UTF</abbr>-8, <abbr title="Unicode Transformation Format">UTF</abbr>-16, and <abbr title="Unicode Transformation Format">UTF</abbr>-32. If <code>SentinelType</code> differs from <code>IteratorType</code>, it must be comparable to the iterator type with <code>operator!=</code>.</p> <p>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-16 and <abbr title="Unicode Transformation Format">UTF</abbr>-32 sequences are rejected: a lone surrogate, a high surrogate that is not followed by its low surrogate, and a code point above <code>U+10FFFF</code> all make this function return <code>false</code>.</p> </li> </ol> <p>Unlike the <a href=../parse/ ><code>parse()</code></a> function, this function neither throws an exception in case of invalid <abbr title="JavaScript Object Notation">JSON</abbr> input (i.e., a parse error) nor creates diagnostic information.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>InputType</code></dt> <dd> <p>A compatible input, for instance:</p> <ul> <li>an <code>std::istream</code> object</li> <li>a <code class=highlight><span class=kt>FILE</span></code> pointer (throws if null)</li> <li>a C-style array of characters</li> <li>a pointer to a null-terminated string of single byte characters (throws if null)</li> <li>a <code>std::string</code> or a <code>std::string_view</code> (C++17)</li> <li>a container <code>obj</code> for which <code>begin(obj)</code> and <code>end(obj)</code> produce a valid pair of iterators (as found via <abbr title="Argument-dependent lookup">ADL</abbr> or member functions, with semantics compatible to <code>std::begin</code> and <code>std::end</code>)</li> <li>wide characters (<code>wchar_t</code>, <code>char16_t</code>, <code>char32_t</code>), which are converted to <abbr title="Unicode Transformation Format">UTF</abbr>-8: a wide string object (<code>std::wstring</code>, <code>std::u16string</code>, <code>std::u32string</code>) or an array (e.g. a wide string literal); a pointer to a null-terminated wide string (e.g. <code>std::u16string::c_str()</code>) is not supported</li> </ul> </dd> <dt><code>IteratorType</code></dt> <dd> <p>a compatible iterator type, for instance.</p> <ul> <li>a pair of <code>std::string::iterator</code> or <code>std::vector&lt;std::uint8_t&gt;::iterator</code></li> <li>a pair of pointers such as <code>ptr</code> and <code>ptr + len</code></li> </ul> </dd> <dt><code>SentinelType</code></dt> <dd> <p>defaults to <code>IteratorType</code>; may be a different type comparable to <code>IteratorType</code> via <code>operator!=</code>, for instance.</p> <ul> <li>a custom sentinel type for C++20 ranges</li> <li><code>std::default_sentinel_t</code>, when <code>IteratorType</code> is <code>std::counted_iterator</code></li> </ul> </dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>i</code> (in)</dt> <dd>Input to parse from.</dd> <dt><code>ignore_comments</code> (in)</dt> <dd>whether comments should be ignored and treated like whitespace (<code class=highlight><span class=nb>true</span></code>) or yield a parse error (<code class=highlight><span class=nb>false</span></code>); (optional, <code class=highlight><span class=nb>false</span></code> by default)</dd> <dt><code>ignore_trailing_commas</code> (in)</dt> <dd>whether trailing commas in arrays or objects should be ignored and treated like whitespace (<code class=highlight><span class=nb>true</span></code>) or yield a parse error (<code class=highlight><span class=nb>false</span></code>); (optional, <code class=highlight><span class=nb>false</span></code> by default)</dd> <dt><code>first</code> (in)</dt> <dd>iterator to the start of the character range</dd> <dt><code>last</code> (in)</dt> <dd>iterator to the end of the character range, or a sentinel value that compares equal to the end iterator with <code>operator!=</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Whether the input is valid <abbr title="JavaScript Object Notation">JSON</abbr>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title=Line truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
<span class=w> </span><span class=c1>// a valid JSON text</span> <span class=w> </span><span class=c1>// a valid JSON text</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>valid_text</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>auto</span><span class=o>*</span><span class=w> </span><span class=n>valid_text</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span>
<span class=s> {</span> <span class=s> {</span>
<span class=s> "numbers": [1, 2, 3]</span> <span class=s> "numbers": [1, 2, 3]</span>
<span class=s> }</span> <span class=s> }</span>
<span class=s> </span><span class=dl>)</span><span class=s>"</span><span class=p>;</span> <span class=s> </span><span class=dl>)</span><span class=s>"</span><span class=p>;</span>
<span class=w> </span><span class=c1>// an invalid JSON text</span> <span class=w> </span><span class=c1>// an invalid JSON text</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>invalid_text</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>auto</span><span class=o>*</span><span class=w> </span><span class=n>invalid_text</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sa>R</span><span class=s>"</span><span class=dl>(</span>
<span class=s> {</span> <span class=s> {</span>
<span class=s> "strings": ["extra", "comma", ]</span> <span class=s> "strings": ["extra", "comma", ]</span>
<span class=s> }</span> <span class=s> }</span>
@@ -40,7 +40,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;vector&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;vector&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -56,7 +56,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;string&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;string&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -71,4 +71,4 @@
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>accept</span><span class=p>(</span><span class=n>invalid_text</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span> <span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>accept</span><span class=p>(</span><span class=n>invalid_text</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span><span class=w> </span><span class=kc>false</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span><span class=w> </span><span class=kc>false</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../parse/ >parse</a> - deserialize from a compatible input</li> <li><a href=../sax_parse/ >sax_parse</a> - parse input using the <abbr title="Simple API for XML">SAX</abbr> interface</li> <li><a href=../../operator_gtgt/ >operator&gt;&gt;</a> - deserialize from stream</li> <li><a href=../../macros/json_strict_nul_handling/ ><code>JSON_STRICT_NUL_HANDLING</code></a> - opt in to rejecting a NUL byte in the input instead of treating it as end of input</li> <li><a href=../../macros/json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a> - read a <code>std::istream</code> one character at a time</li> <li><a href=../../macros/json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a> - read a <code>FILE*</code> with the locking stdio functions</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.0.0.</li> <li>Ignoring comments via <code>ignore_comments</code> added in version 3.9.0.</li> <li>Changed <a href=../../../features/assertions/ >runtime assertion</a> in case of <code>FILE*</code> null pointers to exception in version 3.12.0.</li> <li>Added <code>ignore_trailing_commas</code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li><code>JSON_STRICT_NUL_HANDLING</code> added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to optionally reject a NUL byte in the input instead of treating it as end of input; planned to become the default in version 4.0.0.</li> <li>Parsing from an <code>std::istream</code> scans the characters in its stream buffer in bulk in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> (<a href=../../macros/json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>).</li> <li>Parsing from a <code>FILE*</code> locks the file once instead of once per character in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> (<a href=../../macros/json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a>).</li> <li>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-16 and <abbr title="Unicode Transformation Format">UTF</abbr>-32 input (a lone surrogate, a high surrogate that is not followed by its low surrogate, or a code point above <code>U+10FFFF</code>) is rejected in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; before that, some such sequences were accepted or ended the input silently.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <p>Overload (2) replaces calls to <code>accept</code> with a pair of iterators as their first parameter which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>accept</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>accept</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</p> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="Line truncated </code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../parse/ >parse</a> - deserialize from a compatible input</li> <li><a href=../sax_parse/ >sax_parse</a> - parse input using the <abbr title="Simple API for XML">SAX</abbr> interface</li> <li><a href=../../operator_gtgt/ >operator&gt;&gt;</a> - deserialize from stream</li> <li><a href=../../macros/json_strict_nul_handling/ ><code>JSON_STRICT_NUL_HANDLING</code></a> - opt in to rejecting a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte in the input instead of treating it as end of input</li> <li><a href=../../macros/json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a> - read a <code>std::istream</code> one character at a time</li> <li><a href=../../macros/json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a> - read a <code>FILE*</code> with the locking stdio functions</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.0.0.</li> <li>Ignoring comments via <code>ignore_comments</code> added in version 3.9.0.</li> <li>Changed <a href=../../../features/assertions/ >runtime assertion</a> in case of <code>FILE*</code> null pointers to exception in version 3.12.0.</li> <li>Added <code>ignore_trailing_commas</code> in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended container support (1) to include types with lvalue-only <abbr title="Argument-dependent lookup">ADL</abbr> <code>begin</code>/<code>end</code> (matching <code>std::begin</code>/<code>std::end</code> semantics) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li>Extended overload (2) to accept heterogeneous iterator+sentinel pairs (C++20 ranges support) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> <li><code>JSON_STRICT_NUL_HANDLING</code> added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to optionally reject a <abbr title="Null character (U+0000, byte value 0)">NUL</abbr> byte in the input instead of treating it as end of input; planned to become the default in version 4.0.0.</li> <li>Parsing from an <code>std::istream</code> scans the characters in its stream buffer in bulk in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> (<a href=../../macros/json_disable_stream_bulk_scan/ ><code>JSON_DISABLE_STREAM_BULK_SCAN</code></a>).</li> <li>Parsing from a <code>FILE*</code> locks the file once instead of once per character in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> (<a href=../../macros/json_disable_unlocked_file_io/ ><code>JSON_DISABLE_UNLOCKED_FILE_IO</code></a>).</li> <li>Ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-16 and <abbr title="Unicode Transformation Format">UTF</abbr>-32 input (a lone surrogate, a high surrogate that is not followed by its low surrogate, or a code point above <code>U+10FFFF</code>) is rejected in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>; before that, some such sequences were accepted or ended the input silently.</li> </ul> <div class="admonition warning"> <p class=admonition-title>Deprecation</p> <p>Overload (2) replaces calls to <code>accept</code> with a pair of iterators as their first parameter which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like <code class=highlight><span class=n>accept</span><span class=p>({</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>},</span><span class=w> </span><span class=p>...);</span></code> with <code class=highlight><span class=n>accept</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>ptr</span><span class=o>+</span><span class=n>len</span><span class=p>,</span><span class=w> </span><span class=p>...);</span></code>.</p> <p>You should be warned by your compiler with a <code>-Wdeprecated-declarations</code> warning if you are using a deprecated function.</p> <p>See the <a href=../../../integration/migration_guide/#parsing>migration guide</a> for how to update existing code.</p> </div> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <spaLine truncated
+5 -5
View File
@@ -102,19 +102,19 @@ The example below demonstrates the `accept()` function reading from a string.
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
// a valid JSON text // a valid JSON text
auto valid_text = R"( const auto* valid_text = R"(
{ {
"numbers": [1, 2, 3] "numbers": [1, 2, 3]
} }
)"; )";
// an invalid JSON text // an invalid JSON text
auto invalid_text = R"( const auto* invalid_text = R"(
{ {
"strings": ["extra", "comma", ] "strings": ["extra", "comma", ]
} }
@@ -141,7 +141,7 @@ The example below demonstrates the `accept()` function reading from an iterator
#include <vector> #include <vector>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -169,7 +169,7 @@ The encoding is deduced from the character type of the input. String literals li
#include <string> #include <string>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
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@@ -44,7 +44,7 @@ This function is only needed to express two edge cases that cannot be realized w
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
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@@ -1,8 +1,8 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/array/" rel="canonical"><link href=../accept/ rel=prev><link href=../array_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <divLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/array/" rel="canonical"><link href=../accept/ rel=prev><link href=../array_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonarray class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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</code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> array value from a given initializer list. That is, given a list of values <code>a, b, c</code>, creates the <abbr title="JavaScript Object Notation">JSON</abbr> value <code class=highlight><span class=p>[</span><span class=err>a</span><span class=p>,</span><span class=w> </span><span class=err>b</span><span class=p>,</span><span class=w> </span><span class=err>c</span><span class=p>]</span></code>. If the initializer list is empty, the empty array <code class=highlight><span class=p>[]</span></code> is created.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>init</code> (in)</dt> <dd>initializer list with <abbr title="JavaScript Object Notation">JSON</abbr> values to create an array from (optional)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> array value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of <code>init</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (<a href=../basic_json/ ><code>basic_json(initializer_list_t, bool, value_t)</code></a>). These cases are:</p> <ol> <li>creating an array whose elements are all pairs whose first element is a string -- in this case, the initializer list constructor would create an object, taking the first elements as keys</li> <li>creating an empty array -- passing the empty initializer list to the initializer list constructor yields an empty object</li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for the <code>array</code> function.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> array value from a given initializer list. That is, given a list of values <code>a, b, c</code>, creates the <abbr title="JavaScript Object Notation">JSON</abbr> value <code class=highlight><span class=p>[</span><span class=err>a</span><span class=p>,</span><span class=w> </span><span class=err>b</span><span class=p>,</span><span class=w> </span><span class=err>c</span><span class=p>]</span></code>. If the initializer list is empty, the empty array <code class=highlight><span class=p>[]</span></code> is created.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>init</code> (in)</dt> <dd>initializer list with <abbr title="JavaScript Object Notation">JSON</abbr> values to create an array from (optional)</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> array value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of <code>init</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This function is only needed to express two edge cases that cannot be realized with the initializer list constructor (<a href=../basic_json/ ><code>basic_json(initializer_list_t, bool, value_t)</code></a>). These cases are:</p> <ol> <li>creating an array whose elements are all pairs whose first element is a string -- in this case, the initializer list constructor would create an object, taking the first elements as keys</li> <li>creating an empty array -- passing the empty initializer list to the initializer list constructor yields an empty object</li> </ol> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for the <code>array</code> function.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
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@@ -39,7 +39,7 @@ The following code shows an example for the `array` function.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
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@@ -62,11 +62,11 @@ Arrays are stored as pointers in a `basic_json` type. That is, for any access to
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
std::cout << std::boolalpha << std::is_same<std::vector<json>, json::array_t>::value << std::endl; std::cout << std::boolalpha << std::is_same<std::vector<json>, json::array_t>::value << '\n';
} }
``` ```
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@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/array_t/" rel="canonical"><link href=../array/ rel=prev><link href=../as_base_class/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>array_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> arrays.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> arrays as follows:</p> <blockquote> <p>An array is an ordered sequence of zero or more values.</p> </blockquote> <p>To store objects in C++, a type is defined by the template parameters explained below.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>ArrayType</code></dt> <dd>container type to store arrays. It must be a vector-like container: the library uses <code>operator[]</code>, <code>at()</code>, and <code>resize()</code>, and requires random-access iterators. <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span></code> and <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> qualify; <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span></code> does not. See <a href=../../../features/types/template_parameters/#arraytype>Template Parameter Requirements</a> for the full list of requirements.</dd> <dt><code>AllocatorType</code></dt> <dd>the allocator to use for objects (e.g., <code>std::allocator</code>)</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>With the default values for <code>ArrayType</code> (<code>std::vector</code>) and <code>AllocatorType</code> (<code>std::allocator</code>), the default type for <code>array_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span> </code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> arrays.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> describes <abbr title="JavaScript Object Notation">JSON</abbr> arrays as follows:</p> <blockquote> <p>An array is an ordered sequence of zero or more values.</p> </blockquote> <p>To store objects in C++, a type is defined by the template parameters explained below.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>ArrayType</code></dt> <dd>container type to store arrays. It must be a vector-like container: the library uses <code>operator[]</code>, <code>at()</code>, and <code>resize()</code>, and requires random-access iterators. <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span></code> and <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> qualify; <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>list</span></code> does not. See <a href=../../../features/types/template_parameters/#arraytype>Template Parameter Requirements</a> for the full list of requirements.</dd> <dt><code>AllocatorType</code></dt> <dd>the allocator to use for objects (e.g., <code>std::allocator</code>)</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>With the default values for <code>ArrayType</code> (<code>std::vector</code>) and <code>AllocatorType</code> (<code>std::allocator</code>), the default type for <code>array_t</code> is:</p> <div class=highlight><pre><span></span><code><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span>
<span class=w> </span><span class=n>basic_json</span><span class=p>,</span><span class=w> </span><span class=c1>// value_type</span> <span class=w> </span><span class=n>basic_json</span><span class=p>,</span><span class=w> </span><span class=c1>// value_type</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>allocator</span><span class=o>&lt;</span><span class=n>basic_json</span><span class=o>&gt;</span><span class=w> </span><span class=c1>// allocator_type</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>allocator</span><span class=o>&lt;</span><span class=n>basic_json</span><span class=o>&gt;</span><span class=w> </span><span class=c1>// allocator_type</span>
@@ -7,11 +7,11 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>json</span><span class=o>&gt;</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>array_t</span><span class=o>&gt;::</span><span class=n>value</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>json</span><span class=o>&gt;</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>array_t</span><span class=o>&gt;::</span><span class=n>value</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../object_t/ >object_t</a> the type used to store <abbr title="JavaScript Object Notation">JSON</abbr> objects</li> <li><a href=../binary_t/ >binary_t</a> the type used to store binary values</li> <li><a href=../is_array/ >is_array</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is an array</li> <li><a href=../max_size/ >max_size</a> returns the maximum possible number of elements</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 1.0.0.</li> <li>Made <code>capacity()</code> optional, so that array types such as <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>deque</span></code> can be used, in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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the latest release is 3.12.0.">unreleased</span>.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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+2 -2
View File
@@ -54,11 +54,11 @@ The following code shows that `array_t` is by default, a typedef to `std::vector
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
std::cout << std::boolalpha << std::is_same<std::vector<json>, json::array_t>::value << std::endl; std::cout << std::boolalpha << std::is_same<std::vector<json>, json::array_t>::value << '\n';
} }
``` ```
+1 -1
View File
@@ -1,4 +1,4 @@
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href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonas_base_class class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=k>const</span><span class=w> </span><span class=n>json_base_class_t</span><span class=o>&amp;</span><span class=w> </span><span class=nf>as_base_class</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span> <span class=k>const</span><span class=w> </span><span class=n>json_base_class_t</span><span class=o>&amp;</span><span class=w> </span><span class=nf>as_base_class</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
</code></pre></div> <p>Returns a reference to this object as its custom base class <a href=../json_base_class_t/ ><code>json_base_class_t</code></a>. No copy is made.</p> <p>Since <code>basic_json</code> derives from <code>json_base_class_t</code>, a member of <code>basic_json</code> hides any member of the custom base class with the same name. This function makes such hidden members accessible again.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reference to this object as <a href=../json_base_class_t/ ><code>json_base_class_t</code></a></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>The function is equivalent to <code>static_cast&lt;json_base_class_t&amp;&gt;(j)</code> (or <code>static_cast&lt;const json_base_class_t&amp;&gt;(j)</code>).</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how to use <code>as_base_class</code> to access members of the custom base class that are hidden by members of <code>basic_json</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Returns a reference to this object as its custom base class <a href=../json_base_class_t/ ><code>json_base_class_t</code></a>. No copy is made.</p> <p>Since <code>basic_json</code> derives from <code>json_base_class_t</code>, a member of <code>basic_json</code> hides any member of the custom base class with the same name. This function makes such hidden members accessible again.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reference to this object as <a href=../json_base_class_t/ ><code>json_base_class_t</code></a></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>The function is equivalent to <code>static_cast&lt;json_base_class_t&amp;&gt;(j)</code> (or <code>static_cast&lt;const json_base_class_t&amp;&gt;(j)</code>).</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how to use <code>as_base_class</code> to access members of the custom base class that are hidden by members of <code>basic_json</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
+8 -8
View File
@@ -117,7 +117,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -178,7 +178,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -232,7 +232,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -298,7 +298,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -359,7 +359,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -427,7 +427,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -486,7 +486,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -616,7 +616,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
+9 -9
View File
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/at/" rel="canonical"><link href=../as_base_class/ rel=prev><link href=../back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>at - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=mLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/at/" rel="canonical"><link href=../as_base_class/ rel=prev><link href=../back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>at - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link 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0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=mLine truncated
<span class=n>reference</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>size_type</span><span class=w> </span><span class=n>idx</span><span class=p>);</span> <span class=n>reference</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>size_type</span><span class=w> </span><span class=n>idx</span><span class=p>);</span>
<span class=n>const_reference</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>size_type</span><span class=w> </span><span class=n>idx</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span> <span class=n>const_reference</span><span class=w> </span><span class=nf>at</span><span class=p>(</span><span class=n>size_type</span><span class=w> </span><span class=n>idx</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
@@ -18,7 +18,7 @@
</code></pre></div> <ol> <li>Returns a reference to the array element at specified location <code>idx</code>, with bounds checking.</li> <li>Returns a reference to the object element with specified key <code>key</code>, with bounds checking.</li> <li>See 2. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Returns a reference to the element at specified <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code>, with bounds checking.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>idx</code> (in)</dt> <dd>index of the element to access</dd> <dt><code>key</code> (in)</dt> <dd>object key of the elements to access</dd> <dt><code>ptr</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> pointer to the desired element</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li>reference to the element at index <code>idx</code></li> <li>reference to the element at key <code>key</code></li> <li>reference to the element at key <code>key</code></li> <li>reference to the element pointed to by <code>ptr</code></li> </ol> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <ol> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error304><code>type_error.304</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an array; in this case, calling <code>at</code> with an index makes no sense. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if the index <code>idx</code> is out of range of the array; that is, <code>idx &gt;= size()</code>. See the example below.</li> </ul> </li> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error304><code>type_error.304</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object; in this case, calling <code>at</code> with a key makes no sense. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if the key <code>key</code> is not stored in the object; that is, <code>find(key) == end()</code>. See the example below.</li> </ul> </li> <li>See 2.</li> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error106><code>parse_error.106</code></a> if an array index in the passed <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> begins with '0'. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> if an array index in the passed <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> is not a number. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if an array index in the passed <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> is out of range. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range402><code>out_of_range.402</code></a> if the array index '-' is used in the passed <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code>. As <code>at</code> provides checked access (and no elements are implicitly inserted), the index '-' is always invalid. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> pointer describes a keLine truncated </code></pre></div> <ol> <li>Returns a reference to the array element at specified location <code>idx</code>, with bounds checking.</li> <li>Returns a reference to the object element with specified key <code>key</code>, with bounds checking.</li> <li>See 2. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Returns a reference to the element at specified <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code>, with bounds checking.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>idx</code> (in)</dt> <dd>index of the element to access</dd> <dt><code>key</code> (in)</dt> <dd>object key of the elements to access</dd> <dt><code>ptr</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> pointer to the desired element</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li>reference to the element at index <code>idx</code></li> <li>reference to the element at key <code>key</code></li> <li>reference to the element at key <code>key</code></li> <li>reference to the element pointed to by <code>ptr</code></li> </ol> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <ol> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error304><code>type_error.304</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an array; in this case, calling <code>at</code> with an index makes no sense. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if the index <code>idx</code> is out of range of the array; that is, <code>idx &gt;= size()</code>. See the example below.</li> </ul> </li> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error304><code>type_error.304</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object; in this case, calling <code>at</code> with a key makes no sense. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if the key <code>key</code> is not stored in the object; that is, <code>find(key) == end()</code>. See the example below.</li> </ul> </li> <li>See 2.</li> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error106><code>parse_error.106</code></a> if an array index in the passed <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> begins with '0'. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionparse_error109><code>parse_error.109</code></a> if an array index in the passed <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> is not a number. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if an array index in the passed <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> is out of range. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range402><code>out_of_range.402</code></a> if the array index '-' is used in the passed <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code>. As <code>at</code> provides checked access (and no elements are implicitly inserted), the index '-' is always invalid. See the example below.</li> <li>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range403><code>out_of_range.403</code></a> if the <abbr title="JavaScript Object Notation">JSON</abbr> pointer describes a keLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -64,7 +64,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (1) access specified array element with bounds checking</summary> <p>The example below shows how array elements can be read using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (1) access specified array element with bounds checking</summary> <p>The example below shows how array elements can be read using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -103,7 +103,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (2) access specified object element with bounds checking</summary> <p>The example below shows how object elements can be read and written using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (2) access specified object element with bounds checking</summary> <p>The example below shows how object elements can be read and written using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -154,7 +154,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (2) access specified object element with bounds checking</summary> <p>The example below shows how object elements can be read using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (2) access specified object element with bounds checking</summary> <p>The example below shows how object elements can be read using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -200,7 +200,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -253,7 +253,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -297,7 +297,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (4) access specified element via <abbr title="JavaScript Object Notation">JSON</abbr> Pointer</summary> <p>The example below shows how object elements can be read and written using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (4) access specified element via <abbr title="JavaScript Object Notation">JSON</abbr> Pointer</summary> <p>The example below shows how object elements can be read and written using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
@@ -412,7 +412,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (4) access specified element via <abbr title="JavaScript Object Notation">JSON</abbr> Pointer</summary> <p>The example below shows how object elements can be read using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (4) access specified element via <abbr title="JavaScript Object Notation">JSON</abbr> Pointer</summary> <p>The example below shows how object elements can be read using <code>at()</code>. It also demonstrates the different exceptions that can be thrown.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
+8 -8
View File
@@ -93,7 +93,7 @@ The example below shows how array elements can be read and written using `at()`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -151,7 +151,7 @@ The example below shows how array elements can be read using `at()`. It also dem
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -202,7 +202,7 @@ The example below shows how object elements can be read and written using `at()`
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -265,7 +265,7 @@ The example below shows how object elements can be read using `at()`. It also de
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -323,7 +323,7 @@ The example below shows how object elements can be read and written using `at()`
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -388,7 +388,7 @@ The example below shows how object elements can be read using `at()`. It also de
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -444,7 +444,7 @@ The example below shows how object elements can be read and written using `at()`
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -571,7 +571,7 @@ The example below shows how object elements can be read using `at()`. It also de
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
+1 -1
View File
@@ -49,7 +49,7 @@ Constant.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
View File
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/back/" rel="canonical"><link href=../at/ rel=prev><link href=../begin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div class=md-Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/back/" rel="canonical"><link href=../at/ rel=prev><link href=../begin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonback class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> back </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default 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<span class=n>const_reference</span><span class=w> </span><span class=nf>back</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=p>;</span> <span class=n>const_reference</span><span class=w> </span><span class=nf>back</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
</code></pre></div> <p>Returns a reference to the last element in the container. For a <abbr title="JavaScript Object Notation">JSON</abbr> container <code>c</code>, the expression <code>c.back()</code> is equivalent to</p> <div class=highlight><pre><span></span><code><span class=k>auto</span><span class=w> </span><span class=n>tmp</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>c</span><span class=p>.</span><span class=n>end</span><span class=p>();</span> </code></pre></div> <p>Returns a reference to the last element in the container. For a <abbr title="JavaScript Object Notation">JSON</abbr> container <code>c</code>, the expression <code>c.back()</code> is equivalent to</p> <div class=highlight><pre><span></span><code><span class=k>auto</span><span class=w> </span><span class=n>tmp</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>c</span><span class=p>.</span><span class=n>end</span><span class=p>();</span>
@@ -7,7 +7,7 @@
</code></pre></div> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>In the case of a structured type (array or object), a reference to the last element is returned. In the case of number, string, boolean, or binary values, a reference to the value is returned.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>If the <abbr title="JavaScript Object Notation">JSON</abbr> value is <code class=highlight><span class=kc>null</span></code>, exception <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator214><code>invalid_iterator.214</code></a> is thrown.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Precondition</p> <p>The array or object must not be empty. Calling <code>back</code> on an empty array or object yields undefined behavior.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>back()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>In the case of a structured type (array or object), a reference to the last element is returned. In the case of number, string, boolean, or binary values, a reference to the value is returned.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>If the <abbr title="JavaScript Object Notation">JSON</abbr> value is <code class=highlight><span class=kc>null</span></code>, exception <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator214><code>invalid_iterator.214</code></a> is thrown.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition info"> <p class=admonition-title>Precondition</p> <p>The array or object must not be empty. Calling <code>back</code> on an empty array or object yields undefined behavior.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>back()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
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@@ -46,7 +46,7 @@ The following code shows an example for `back()`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+10 -10
View File
@@ -349,7 +349,7 @@ basic_json(basic_json&& other) noexcept;
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -395,7 +395,7 @@ basic_json(basic_json&& other) noexcept;
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -434,7 +434,7 @@ basic_json(basic_json&& other) noexcept;
#include <valarray> #include <valarray>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -698,8 +698,8 @@ basic_json(basic_json&& other) noexcept;
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using ordered_json = nlohmann::ordered_json; using nlohmann::ordered_json;
int main() int main()
{ {
@@ -737,7 +737,7 @@ basic_json(basic_json&& other) noexcept;
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -777,7 +777,7 @@ basic_json(basic_json&& other) noexcept;
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -812,7 +812,7 @@ basic_json(basic_json&& other) noexcept;
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -862,7 +862,7 @@ basic_json(basic_json&& other) noexcept;
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -895,7 +895,7 @@ basic_json(basic_json&& other) noexcept;
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+11 -11
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@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/basic_json/" rel="canonical"><link href=../ rel=prev><link href=../~basic_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>(Constructor) - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/basic_json/" rel="canonical"><link href=../ rel=prev><link href=../~basic_json/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>(Constructor) - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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<span class=n>basic_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>value_t</span><span class=w> </span><span class=n>v</span><span class=p>);</span> <span class=n>basic_json</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>value_t</span><span class=w> </span><span class=n>v</span><span class=p>);</span>
<span class=c1>// (2)</span> <span class=c1>// (2)</span>
@@ -48,7 +48,7 @@
</code></pre></div> <p>See the <abbr title="Frequently Asked Questions">FAQ</abbr> entry on <a href=../../../home/faq/#brace-initialization-yields-arrays>brace initialization</a> for the full explanation, an opt-in macro to change this behavior, and how to explicitly create a single-element array (<code>json::array({value})</code>) if that is what you want.</p> </div> </li> <li> <p>Constructs a <abbr title="JavaScript Object Notation">JSON</abbr> array value by creating <code>cnt</code> copies of a passed value. In case <code>cnt</code> is <code>0</code>, an empty array is created.</p> </li> <li> <p>Constructs the <abbr title="JavaScript Object Notation">JSON</abbr> value with the contents of the range <code>[first, last)</code>. The semantics depend on the different types a <abbr title="JavaScript Object Notation">JSON</abbr> value can have:</p> <ul> <li>In case of a <code class=highlight><span class=kc>null</span></code> type, <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator206>invalid_iterator.206</a> is thrown.</li> <li>In case of other primitive types (number, boolean, string, or binary), <code>first</code> must be <code>begin()</code> and <code>last</code> must be <code>end()</code>. In this case, the value is copied. Otherwise, <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator204><code>invalid_iterator.204</code></a> is thrown.</li> <li>In case of structured types (array, object), the constructor behaves as similar versions for <code>std::vector</code> or <code>std::map</code>; that is, a <abbr title="JavaScript Object Notation">JSON</abbr> array or object is constructed from the values in the range.</li> </ul> </li> <li> <p>Creates a copy of a given <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> </li> <li> <p>Move constructor. Constructs a <abbr title="JavaScript Object Notation">JSON</abbr> value with the contents of the given value <code>other</code> using move semantics. It "steals" the resources from <code>other</code> and leaves it as <abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=kc>null</span></code> value.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>CompatibleType</code></dt> <dd> <p>a type such that:</p> <ul> <li><code>CompatibleType</code> is not derived from <code>std::istream</code>,</li> <li><code>CompatibleType</code> is not <code>basic_json</code> (to avoid hijacking copy/move constructors),</li> <li><code>CompatibleType</code> is not a different <code>basic_json</code> type (i.e. with different template arguments)</li> <li><code>CompatibleType</code> is not a <code>basic_json</code> nested type (e.g., <code>json_pointer</code>, <code>iterator</code>, etc.)</li> <li>if <a href=../../macros/json_disable_tuple_reference_conversion/ ><code>JSON_DISABLE_TUPLE_REFERENCE_CONVERSION</code></a> is defined to <code>1</code>: <code>CompatibleType</code> is not a one-element <code>std::tuple</code> holding a reference to <code>basic_json</code></li> <li><code>json_serializer&lt;U&gt;</code> (with <code>U = uncvref_t&lt;CompatibleType&gt;</code>) has a <code>to_json(basic_json_t&amp;, CompatibleType&amp;&amp;)</code> method</li> </ul> </dd> <dt><code>BasicJsonType</code>:</dt> <dd> <p>a type such that:</p> <ul> <li><code>BasicJsonType</code> is a <code>basic_json</code> type.</li> <li><code>BasicJsonType</code> has different template arguments than <code>basic_json_t</code>.</li> </ul> <p><strong>Note:</strong> For cross-<code>basic_json</code> conversions to produce correct results, the target <code>basic_json</code>'s <a href=../object_t/ ><code>object_t</code></a><code>::key_type</code> and <a href=../string_t/ ><code>string_t</code></a> must be directly constructible from the source <code>basic_json</code>'s corresponding types. See the description of overload (4) above for details on what happens when this requirement is not met.</p> </dd> <dt><code>U</code>:</dt> <dd><code>uncvref_t&lt;CompatibleType&gt;</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>v</code> (in)</dt> <dd>the type of the value to create</dd> <dt><code>val</code> (in)</dt> <dd>the value to be forwarded to the respective constructor</dd> <dt><code>init</code> (in)</dt> <dd>initializer list with <abbr title="JavaScript Object Notation">JSON</abbr> values</dd> <dt><code>type_deduction</code> (in)</dt> <dd>internal parameter; when set to <code class=highlight><span class=nb>true</span></code>, the type of the <abbr title="JavaScript Object Notation">JSON</abbr> value is deducted from the initializer list <code>init</code>; when set to <code class=highlight><span class=nb>false</span></code>, the type provided via <code>manual_type</code> is forced. This mode is used by the functions <code>array(initializer_list_t)</code> and <code>object(Line truncated </code></pre></div> <p>See the <abbr title="Frequently Asked Questions">FAQ</abbr> entry on <a href=../../../home/faq/#brace-initialization-yields-arrays>brace initialization</a> for the full explanation, an opt-in macro to change this behavior, and how to explicitly create a single-element array (<code>json::array({value})</code>) if that is what you want.</p> </div> </li> <li> <p>Constructs a <abbr title="JavaScript Object Notation">JSON</abbr> array value by creating <code>cnt</code> copies of a passed value. In case <code>cnt</code> is <code>0</code>, an empty array is created.</p> </li> <li> <p>Constructs the <abbr title="JavaScript Object Notation">JSON</abbr> value with the contents of the range <code>[first, last)</code>. The semantics depend on the different types a <abbr title="JavaScript Object Notation">JSON</abbr> value can have:</p> <ul> <li>In case of a <code class=highlight><span class=kc>null</span></code> type, <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator206>invalid_iterator.206</a> is thrown.</li> <li>In case of other primitive types (number, boolean, string, or binary), <code>first</code> must be <code>begin()</code> and <code>last</code> must be <code>end()</code>. In this case, the value is copied. Otherwise, <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator204><code>invalid_iterator.204</code></a> is thrown.</li> <li>In case of structured types (array, object), the constructor behaves as similar versions for <code>std::vector</code> or <code>std::map</code>; that is, a <abbr title="JavaScript Object Notation">JSON</abbr> array or object is constructed from the values in the range.</li> </ul> </li> <li> <p>Creates a copy of a given <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> </li> <li> <p>Move constructor. Constructs a <abbr title="JavaScript Object Notation">JSON</abbr> value with the contents of the given value <code>other</code> using move semantics. It "steals" the resources from <code>other</code> and leaves it as <abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=kc>null</span></code> value.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>CompatibleType</code></dt> <dd> <p>a type such that:</p> <ul> <li><code>CompatibleType</code> is not derived from <code>std::istream</code>,</li> <li><code>CompatibleType</code> is not <code>basic_json</code> (to avoid hijacking copy/move constructors),</li> <li><code>CompatibleType</code> is not a different <code>basic_json</code> type (i.e. with different template arguments)</li> <li><code>CompatibleType</code> is not a <code>basic_json</code> nested type (e.g., <code>json_pointer</code>, <code>iterator</code>, etc.)</li> <li>if <a href=../../macros/json_disable_tuple_reference_conversion/ ><code>JSON_DISABLE_TUPLE_REFERENCE_CONVERSION</code></a> is defined to <code>1</code>: <code>CompatibleType</code> is not a one-element <code>std::tuple</code> holding a reference to <code>basic_json</code></li> <li><code>json_serializer&lt;U&gt;</code> (with <code>U = uncvref_t&lt;CompatibleType&gt;</code>) has a <code>to_json(basic_json_t&amp;, CompatibleType&amp;&amp;)</code> method</li> </ul> </dd> <dt><code>BasicJsonType</code>:</dt> <dd> <p>a type such that:</p> <ul> <li><code>BasicJsonType</code> is a <code>basic_json</code> type.</li> <li><code>BasicJsonType</code> has different template arguments than <code>basic_json_t</code>.</li> </ul> <p><strong>Note:</strong> For cross-<code>basic_json</code> conversions to produce correct results, the target <code>basic_json</code>'s <a href=../object_t/ ><code>object_t</code></a><code>::key_type</code> and <a href=../string_t/ ><code>string_t</code></a> must be directly constructible from the source <code>basic_json</code>'s corresponding types. See the description of overload (4) above for details on what happens when this requirement is not met.</p> </dd> <dt><code>U</code>:</dt> <dd><code>uncvref_t&lt;CompatibleType&gt;</code></dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>v</code> (in)</dt> <dd>the type of the value to create</dd> <dt><code>val</code> (in)</dt> <dd>the value to be forwarded to the respective constructor</dd> <dt><code>init</code> (in)</dt> <dd>initializer list with <abbr title="JavaScript Object Notation">JSON</abbr> values</dd> <dt><code>type_deduction</code> (in)</dt> <dd>internal parameter; when set to <code class=highlight><span class=nb>true</span></code>, the type of the <abbr title="JavaScript Object Notation">JSON</abbr> value is deducted from the initializer list <code>init</code>; when set to <code class=highlight><span class=nb>false</span></code>, the type provided via <code>manual_type</code> is forced. This mode is used by the functions <code>array(initializer_list_t)</code> and <code>object(Line truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -80,7 +80,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (2) create a <code class=highlight><span class=kc>null</span></code> object</summary> <p>The following code shows the constructor with and without a null pointer parameter.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (2) create a <code class=highlight><span class=kc>null</span></code> object</summary> <p>The following code shows the constructor with and without a null pointer parameter.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -105,7 +105,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;valarray&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;valarray&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -351,8 +351,8 @@
</code></pre></div> <p>Note the output is platform-dependent.</p> </details> <details class=example> <summary>Example: (4) create a <abbr title="JavaScript Object Notation">JSON</abbr> value from another <code>basic_json</code> specialization</summary> <p>The example below shows how a <code>json</code> value is converted to an <code>ordered_json</code> value and back using the converting constructor. Note how the original insertion order of <code>oj</code> is not restored, because it was already given up when converting to <code>json</code>, whose <code>object_t</code> sorts by key.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Note the output is platform-dependent.</p> </details> <details class=example> <summary>Example: (4) create a <abbr title="JavaScript Object Notation">JSON</abbr> value from another <code>basic_json</code> specialization</summary> <p>The example below shows how a <code>json</code> value is converted to an <code>ordered_json</code> value and back using the converting constructor. Note how the original insertion order of <code>oj</code> is not restored, because it was already given up when converting to <code>json</code>, whose <code>object_t</code> sorts by key.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>ordered_json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>ordered_json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>ordered_json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -376,7 +376,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (5) create a container (array or object) from an initializer list</summary> <p>The example below shows how <abbr title="JavaScript Object Notation">JSON</abbr> values are created from initializer lists.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (5) create a container (array or object) from an initializer list</summary> <p>The example below shows how <abbr title="JavaScript Object Notation">JSON</abbr> values are created from initializer lists.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -402,7 +402,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (6) construct an array with count copies of a given value</summary> <p>The following code shows examples for creating arrays with several copies of a given value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (6) construct an array with count copies of a given value</summary> <p>The following code shows examples for creating arrays with several copies of a given value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -423,7 +423,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (7) construct a <abbr title="JavaScript Object Notation">JSON</abbr> container given an iterator range</summary> <p>The example below shows several ways to create <abbr title="JavaScript Object Notation">JSON</abbr> values by specifying a subrange with iterators.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (7) construct a <abbr title="JavaScript Object Notation">JSON</abbr> container given an iterator range</summary> <p>The example below shows several ways to create <abbr title="JavaScript Object Notation">JSON</abbr> values by specifying a subrange with iterators.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -459,7 +459,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (8) copy constructor</summary> <p>The following code shows an example for the copy constructor.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (8) copy constructor</summary> <p>The following code shows an example for the copy constructor.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -478,7 +478,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (9) move constructor</summary> <p>The code below shows the move constructor explicitly called via <code>std::move</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (9) move constructor</summary> <p>The code below shows the move constructor explicitly called via <code>std::move</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+10 -10
View File
@@ -271,7 +271,7 @@ The following code shows the constructor for different `value_t` values.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -315,7 +315,7 @@ The following code shows the constructor with and without a null pointer paramet
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -352,7 +352,7 @@ The following code shows the constructor with several compatible types.
#include <valarray> #include <valarray>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -612,8 +612,8 @@ The example below shows how a `json` value is converted to an `ordered_json` val
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using ordered_json = nlohmann::ordered_json; using nlohmann::ordered_json;
int main() int main()
{ {
@@ -649,7 +649,7 @@ The example below shows how JSON values are created from initializer lists.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -687,7 +687,7 @@ The following code shows examples for creating arrays with several copies of a g
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -720,7 +720,7 @@ The example below shows several ways to create JSON values by specifying a subra
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -768,7 +768,7 @@ The following code shows an example for the copy constructor.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -799,7 +799,7 @@ The code below shows the move constructor explicitly called via `std::move`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+1 -1
View File
@@ -31,7 +31,7 @@ Constant.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
View File
@@ -1,9 +1,9 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/begin/" rel="canonical"><link href=../back/ rel=prev><link href=../binary/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>begin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div clLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/begin/" rel="canonical"><link href=../back/ rel=prev><link href=../binary/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>begin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonbegin class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> begin </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=n>const_iterator</span><span class=w> </span><span class=nf>begin</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span> <span class=n>const_iterator</span><span class=w> </span><span class=nf>begin</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
</code></pre></div> <p>Returns an iterator to the first element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>begin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Returns an iterator to the first element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>begin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
View File
@@ -29,7 +29,7 @@ The following code shows an example for `begin()`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
View File
@@ -55,7 +55,7 @@ initialization of a binary array type, for backwards compatibility and so it doe
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -66,7 +66,7 @@ initialization of a binary array type, for backwards compatibility and so it doe
json j = json::binary(vec, 42); json j = json::binary(vec, 42);
// output type and subtype // output type and subtype
std::cout << "type: " << j.type_name() << ", subtype: " << j.get_binary().subtype() << std::endl; std::cout << "type: " << j.type_name() << ", subtype: " << j.get_binary().subtype() << '\n';
} }
``` ```
+3 -3
View File
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/binary/" rel="canonical"><link href=../begin/ rel=prev><link href=../binary_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>binary - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> binary </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" type=radio name=__palette id=__palette_0> <label class="md-header__button md-icon" title="Switch to dark mode" for=__palette_1 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a4 4 0 0 0-4 4 4 4 0 0 0 4 4 4 4 0 0 0 4-4 4 4 0 0 0-4-4m0 10a6 6 0 0 1-6-6 6 6 0 0 1 6-6 6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> <input class=md-option data-md-color-media="(prefers-color-scheme: dark)" data-md-color-scheme=slate data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to light mode" type=radio name=__palette id=__palette_1> <label class="md-header__button md-icon" title="Switch to light mode" for=__palette_0 hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 18c-.89 0-1.74-.2-2.5-.55C11.56 16.5 13 14.42 13 12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/binary/" rel="canonical"><link href=../begin/ rel=prev><link href=../binary_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>binary - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> binary </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=nf>binary</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>binary_t</span><span class=o>::</span><span class=n>container_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>init</span><span class=p>);</span> <span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=nf>binary</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>binary_t</span><span class=o>::</span><span class=n>container_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>init</span><span class=p>);</span>
<span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=nf>binary</span><span class=p>(</span><span class=k>typename</span><span class=w> </span><span class=nc>binary_t</span><span class=o>::</span><span class=n>container_type</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>init</span><span class=p>);</span> <span class=k>static</span><span class=w> </span><span class=n>basic_json</span><span class=w> </span><span class=nf>binary</span><span class=p>(</span><span class=k>typename</span><span class=w> </span><span class=nc>binary_t</span><span class=o>::</span><span class=n>container_type</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>init</span><span class=p>);</span>
@@ -10,7 +10,7 @@
</code></pre></div> <ol> <li>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> binary array value from a given binary container.</li> <li>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> binary array value from a given binary container with subtype.</li> </ol> <p>Binary values are part of various binary formats, such as <abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, and <abbr title="Binary JSON">BSON</abbr>. This constructor is used to create a value for serialization to those formats.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>init</code> (in)</dt> <dd>container containing bytes to use as a binary type</dd> <dt><code>subtype</code> (in)</dt> <dd>subtype to use in <abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, and <abbr title="Binary JSON">BSON</abbr></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> binary array value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of <code>init</code>; constant for <code>typename binary_t::container_type&amp;&amp; init</code> versions.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Note, this function exists because of the difficulty in correctly specifying the correct template overload in the standard value ctor, as both <abbr title="JavaScript Object Notation">JSON</abbr> arrays and <abbr title="JavaScript Object Notation">JSON</abbr> binary arrays are backed with some form of a <code>std::vector</code>. Because <abbr title="JavaScript Object Notation">JSON</abbr> binary arrays are a non-standard extension, it was decided that it would be best to prevent automatic initialization of a binary array type, for backwards compatibility and so it does not happen on accident.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how to create a binary value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <ol> <li>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> binary array value from a given binary container.</li> <li>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> binary array value from a given binary container with subtype.</li> </ol> <p>Binary values are part of various binary formats, such as <abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, and <abbr title="Binary JSON">BSON</abbr>. This constructor is used to create a value for serialization to those formats.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>init</code> (in)</dt> <dd>container containing bytes to use as a binary type</dd> <dt><code>subtype</code> (in)</dt> <dd>subtype to use in <abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, and <abbr title="Binary JSON">BSON</abbr></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><abbr title="JavaScript Object Notation">JSON</abbr> binary array value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes in the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of <code>init</code>; constant for <code>typename binary_t::container_type&amp;&amp; init</code> versions.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Note, this function exists because of the difficulty in correctly specifying the correct template overload in the standard value ctor, as both <abbr title="JavaScript Object Notation">JSON</abbr> arrays and <abbr title="JavaScript Object Notation">JSON</abbr> binary arrays are backed with some form of a <code>std::vector</code>. Because <abbr title="JavaScript Object Notation">JSON</abbr> binary arrays are a non-standard extension, it was decided that it would be best to prevent automatic initialization of a binary array type, for backwards compatibility and so it does not happen on accident.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how to create a binary value.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -21,7 +21,7 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>(</span><span class=n>vec</span><span class=p>,</span><span class=w> </span><span class=mi>42</span><span class=p>);</span> <span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>(</span><span class=n>vec</span><span class=p>,</span><span class=w> </span><span class=mi>42</span><span class=p>);</span>
<span class=w> </span><span class=c1>// output type and subtype</span> <span class=w> </span><span class=c1>// output type and subtype</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"type: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>type_name</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", subtype: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get_binary</span><span class=p>().</span><span class=n>subtype</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"type: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>type_name</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>", subtype: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get_binary</span><span class=p>().</span><span class=n>subtype</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>t</span><span class=err>ype</span><span class=p>:</span><span class=w> </span><span class=err>bi</span><span class=kc>nar</span><span class=err>y</span><span class=p>,</span><span class=w> </span><span class=err>sub</span><span class=kc>t</span><span class=err>ype</span><span class=p>:</span><span class=w> </span><span class=mi>42</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>t</span><span class=err>ype</span><span class=p>:</span><span class=w> </span><span class=err>bi</span><span class=kc>nar</span><span class=err>y</span><span class=p>,</span><span class=w> </span><span class=err>sub</span><span class=kc>t</span><span class=err>ype</span><span class=p>:</span><span class=w> </span><span class=mi>42</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../binary_t/ >binary_t</a> type for binary values</li> <li><a href=../get_binary/ >get_binary</a> get a reference to the stored binary value</li> <li><a href=../is_binary/ >is_binary</a> return whether the value is binary</li> <li><a href=../../byte_container_with_subtype/ >byte_container_with_subtype</a> container for binary values with subtype</li> <li><a href=../../../features/binary_values/ >Binary Values</a> - the article on binary values</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.8.0.</li> <li>Changed the type of <code>subtype</code> from <code>std::uint8_t</code> to <code>binary_t::subtype_type</code> (<code>std::uint64_t</code>) in version 3.10.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 2, 2026 09:32:15 UTC">October 2, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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+2 -2
View File
@@ -49,7 +49,7 @@ The following code shows how to create a binary value.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -60,7 +60,7 @@ int main()
json j = json::binary(vec, 42); json j = json::binary(vec, 42);
// output type and subtype // output type and subtype
std::cout << "type: " << j.type_name() << ", subtype: " << j.get_binary().subtype() << std::endl; std::cout << "type: " << j.type_name() << ", subtype: " << j.get_binary().subtype() << '\n';
} }
``` ```
+5 -4
View File
@@ -90,8 +90,9 @@ type `#!cpp binary_t*` must be dereferenced.
- MessagePack - MessagePack
- If a subtype is given and the binary array contains exactly 1, 2, 4, 8, or 16 elements, the fixext family (fixext1, - If a subtype is given and the binary array contains exactly 1, 2, 4, 8, or 16 elements, the fixext family (fixext1,
fixext2, fixext4, fixext8) is used. For other sizes, the ext family (ext8, ext16, ext32) is used. The subtype is fixext2, fixext4, fixext8, fixext16) is used. For other sizes, the ext family (ext8, ext16, ext32) is used. The
then added as a signed 8-bit integer. subtype is then written as the signed 8-bit ext type: subtypes 128 to 255 map to the negative (reserved) ext
types, and on reading the ext type is exposed as an unsigned subtype from 0 to 255.
- If no subtype is given, the bin family (bin8, bin16, bin32) is used. - If no subtype is given, the bin family (bin8, bin16, bin32) is used.
- BSON - BSON
@@ -110,11 +111,11 @@ type `#!cpp binary_t*` must be dereferenced.
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
std::cout << std::boolalpha << std::is_same<nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>, json::binary_t>::value << std::endl; std::cout << std::boolalpha << std::is_same<nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>, json::binary_t>::value << '\n';
} }
``` ```
+5 -5
View File
@@ -1,4 +1,4 @@
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</code></pre></div> <p>This type is a type designed to carry binary data that appears in various serialized formats, such as <abbr title="Concise Binary Object Representation">CBOR</abbr>'s Major Type 2, MessagePack's bin, and <abbr title="Binary JSON">BSON</abbr>'s generic binary subtype. This type is NOT a part of standard <abbr title="JavaScript Object Notation">JSON</abbr> and exists solely for compatibility with these binary types. As such, it is simply defined as an ordered sequence of zero or more byte values.</p> <p>Additionally, as an implementation detail, the subtype of the binary data is carried around as a <code>std::uint64_t</code>, which is compatible with both of the binary data formats that use binary subtyping, (though the specific numbering is incompatible with each other, and it is up to the user to translate between them). The subtype is added to <code>BinaryType</code> via the helper type <a href=../../byte_container_with_subtype/ >byte_container_with_subtype</a>.</p> <p><a href="https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1"><abbr title="Concise Binary Object Representation">CBOR</abbr>'s <abbr title="Request for Comments">RFC</abbr> 8949</a> describes this type as:</p> <blockquote> <p>Major type 2: A byte string. The number of bytes in the string is equal to the argument.</p> </blockquote> <p><a href="https://github.com/msgpack/msgpack/blob/master/spec.md#bin-format-family">MessagePack's documentation on the bin type family</a> describes this type as:</p> <blockquote> <p>Bin format family stores a byte array in 2, 3, or 5 bytes of extra bytes in addition to the size of the byte array.</p> </blockquote> <p><a href="http://bsonspec.org/spec.html"><abbr title="Binary JSON">BSON</abbr>'s specifications</a> describe several binary types; however, this type is intended to represent the generic binary type which has the description:</p> <blockquote> <p>Generic binary subtype - This is the most commonly used binary subtype and should be the 'default' for drivers and tools.</p> </blockquote> <p>None of these impose any limitations on the internal representation other than the basic unit of storage be some type of array whose parts are decomposable into bytes.</p> <p>The default representation of this binary format is a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>, which is a very common way to represent a byte array in modern C++.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BinaryType</code></dt> <dd> <p>container type to store arrays</p> <p>Although not formally expressed as a C++ concept, <code>BinaryType</code> must be default-constructible, copy/move-constructible, and support <code>push_back()</code>, <code>.data()</code>, and <code>.size()</code>, because <a href=../../byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a> derives directly from it. Its <code>value_type</code> must additionally be exactly one byte wide (e.g., <code>std::uint8_t</code>/<code>char</code>/<code>std::byte</code>): the binary serializers (<abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, <abbr title="Binary JSON">BSON</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>) read and write the container's raw bytes via <code>reinterpret_cast</code>, which is only correct for byte-sized elements -- a container like <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>intptr_t</span><span class=o>&gt;</span></code> will not work as <code>BinaryType</code>. The elements must be stored contiguously, and the binary readers additionally require <code>resize()</code> and <code>operator[]</code>. See <a href=../../../features/types/template_parameters/#binarytype>Template Parameter Requirements</a> for the full list.</p> </dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>The default values for <code>BinaryType</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>.</p> <h3 id=supported-byte-types>Supported byte types<a class=headerlink href=#supported-byte-types title="Permanent link">&para;</a></h3> <p><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span clLine truncated </code></pre></div> <p>This type is a type designed to carry binary data that appears in various serialized formats, such as <abbr title="Concise Binary Object Representation">CBOR</abbr>'s Major Type 2, MessagePack's bin, and <abbr title="Binary JSON">BSON</abbr>'s generic binary subtype. This type is NOT a part of standard <abbr title="JavaScript Object Notation">JSON</abbr> and exists solely for compatibility with these binary types. As such, it is simply defined as an ordered sequence of zero or more byte values.</p> <p>Additionally, as an implementation detail, the subtype of the binary data is carried around as a <code>std::uint64_t</code>, which is compatible with both of the binary data formats that use binary subtyping, (though the specific numbering is incompatible with each other, and it is up to the user to translate between them). The subtype is added to <code>BinaryType</code> via the helper type <a href=../../byte_container_with_subtype/ >byte_container_with_subtype</a>.</p> <p><a href="https://www.rfc-editor.org/rfc/rfc8949.html#section-3.1"><abbr title="Concise Binary Object Representation">CBOR</abbr>'s <abbr title="Request for Comments">RFC</abbr> 8949</a> describes this type as:</p> <blockquote> <p>Major type 2: A byte string. The number of bytes in the string is equal to the argument.</p> </blockquote> <p><a href="https://github.com/msgpack/msgpack/blob/master/spec.md#bin-format-family">MessagePack's documentation on the bin type family</a> describes this type as:</p> <blockquote> <p>Bin format family stores a byte array in 2, 3, or 5 bytes of extra bytes in addition to the size of the byte array.</p> </blockquote> <p><a href="http://bsonspec.org/spec.html"><abbr title="Binary JSON">BSON</abbr>'s specifications</a> describe several binary types; however, this type is intended to represent the generic binary type which has the description:</p> <blockquote> <p>Generic binary subtype - This is the most commonly used binary subtype and should be the 'default' for drivers and tools.</p> </blockquote> <p>None of these impose any limitations on the internal representation other than the basic unit of storage be some type of array whose parts are decomposable into bytes.</p> <p>The default representation of this binary format is a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>, which is a very common way to represent a byte array in modern C++.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BinaryType</code></dt> <dd> <p>container type to store arrays</p> <p>Although not formally expressed as a C++ concept, <code>BinaryType</code> must be default-constructible, copy/move-constructible, and support <code>push_back()</code>, <code>.data()</code>, and <code>.size()</code>, because <a href=../../byte_container_with_subtype/ ><code>byte_container_with_subtype</code></a> derives directly from it. Its <code>value_type</code> must additionally be exactly one byte wide (e.g., <code>std::uint8_t</code>/<code>char</code>/<code>std::byte</code>): the binary serializers (<abbr title="Concise Binary Object Representation">CBOR</abbr>, MessagePack, <abbr title="Binary JSON">BSON</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>) read and write the container's raw bytes via <code>reinterpret_cast</code>, which is only correct for byte-sized elements -- a container like <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>intptr_t</span><span class=o>&gt;</span></code> will not work as <code>BinaryType</code>. The elements must be stored contiguously, and the binary readers additionally require <code>resize()</code> and <code>operator[]</code>. See <a href=../../../features/types/template_parameters/#binarytype>Template Parameter Requirements</a> for the full list.</p> </dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>The default values for <code>BinaryType</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code>.</p> <h3 id=supported-byte-types>Supported byte types<a class=headerlink href=#supported-byte-types title="Permanent link">&para;</a></h3> <p><code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span clLine truncated
<span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>&gt;</span><span class=w> </span><span class=n>data</span><span class=p>{</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>1</span><span class=p>},</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>2</span><span class=p>},</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>3</span><span class=p>}};</span> <span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>&gt;</span><span class=w> </span><span class=n>data</span><span class=p>{</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>1</span><span class=p>},</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>2</span><span class=p>},</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=p>{</span><span class=mi>3</span><span class=p>}};</span>
@@ -8,15 +8,15 @@
<span class=c1>// Round-tripping works seamlessly</span> <span class=c1>// Round-tripping works seamlessly</span>
<span class=k>auto</span><span class=w> </span><span class=n>extracted</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>&gt;&gt;</span><span class=p>();</span> <span class=k>auto</span><span class=w> </span><span class=n>extracted</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>get</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>byte</span><span class=o>&gt;&gt;</span><span class=p>();</span>
<span class=n>assert</span><span class=p>(</span><span class=n>extracted</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>data</span><span class=p>);</span> <span class=n>assert</span><span class=p>(</span><span class=n>extracted</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>data</span><span class=p>);</span>
</code></pre></div> <p>This automatic type detection is a convenience feature that only applies to custom (non-default) <code>BinaryType</code> configurations. The default <code>nlohmann::json</code> continues to treat <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code> as arrays for backward compatibility.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">&para;</a></h3> <p>Binary Arrays are stored as pointers in a <code>basic_json</code> type. That is, for any access to array values, a pointer of the type <code class=highlight><span class=n>binary_t</span><span class=o>*</span></code> must be dereferenced.</p> <h3 id=notes-on-subtypes>Notes on subtypes<a class=headerlink href=#notes-on-subtypes title="Permanent link">&para;</a></h3> <ul> <li> <p><abbr title="Concise Binary Object Representation">CBOR</abbr></p> <ul> <li>Binary values are represented as byte strings. Subtypes are written as tags.</li> </ul> </li> <li> <p>MessagePack</p> <ul> <li>If a subtype is given and the binary array contains exactly 1, 2, 4, 8, or 16 elements, the fixext family (fixext1, fixext2, fixext4, fixext8) is used. For other sizes, the ext family (ext8, ext16, ext32) is used. The subtype is then added as a signed 8-bit integer.</li> <li>If no subtype is given, the bin family (bin8, bin16, bin32) is used.</li> </ul> </li> <li> <p><abbr title="Binary JSON">BSON</abbr></p> <ul> <li>If a subtype is given, it is used and added as an unsigned 8-bit integer.</li> <li>If no subtype is given, the generic binary subtype 0x00 is used.</li> </ul> </li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>binary_t</code> is by default, a typedef to <code class=highlight><span class=n>nlohmann</span><span class=o>::</span><span class=n>byte_container_with_subtype</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;&gt;</span></code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>This automatic type detection is a convenience feature that only applies to custom (non-default) <code>BinaryType</code> configurations. The default <code>nlohmann::json</code> continues to treat <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;</span></code> as arrays for backward compatibility.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">&para;</a></h3> <p>Binary Arrays are stored as pointers in a <code>basic_json</code> type. That is, for any access to array values, a pointer of the type <code class=highlight><span class=n>binary_t</span><span class=o>*</span></code> must be dereferenced.</p> <h3 id=notes-on-subtypes>Notes on subtypes<a class=headerlink href=#notes-on-subtypes title="Permanent link">&para;</a></h3> <ul> <li> <p><abbr title="Concise Binary Object Representation">CBOR</abbr></p> <ul> <li>Binary values are represented as byte strings. Subtypes are written as tags.</li> </ul> </li> <li> <p>MessagePack</p> <ul> <li>If a subtype is given and the binary array contains exactly 1, 2, 4, 8, or 16 elements, the fixext family (fixext1, fixext2, fixext4, fixext8, fixext16) is used. For other sizes, the ext family (ext8, ext16, ext32) is used. The subtype is then written as the signed 8-bit ext type: subtypes 128 to 255 map to the negative (reserved) ext types, and on reading the ext type is exposed as an unsigned subtype from 0 to 255.</li> <li>If no subtype is given, the bin family (bin8, bin16, bin32) is used.</li> </ul> </li> <li> <p><abbr title="Binary JSON">BSON</abbr></p> <ul> <li>If a subtype is given, it is used and added as an unsigned 8-bit integer.</li> <li>If no subtype is given, the generic binary subtype 0x00 is used.</li> </ul> </li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>binary_t</code> is by default, a typedef to <code class=highlight><span class=n>nlohmann</span><span class=o>::</span><span class=n>byte_container_with_subtype</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;&gt;</span></code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o>&lt;</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>byte_container_with_subtype</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;&gt;</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary_t</span><span class=o>&gt;::</span><span class=n>value</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o>&lt;</span><span class=n>nlohmann</span><span class=o>::</span><span class=n>byte_container_with_subtype</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;&gt;</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary_t</span><span class=o>&gt;::</span><span class=n>value</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../../byte_container_with_subtype/ >byte_container_with_subtype</a></li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.8.0. Changed the type of subtype to <code>std::uint64_t</code> in version 3.10.0.</li> <li>Fixed <a href=../dump/ ><code>dump</code></a>, <a href=../std_hash/ ><code>std::hash</code></a>, and <a href=../to_ubjson/ ><code>to_ubjson</code></a> for byte types that are not integers (e.g., <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>byte</span></code>) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>. <code>dump</code> now writes the bytes of a signed byte type (e.g., <code class=highlight><span class=kt>char</span></code>) as 0..255 rather than as negative numbers.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 9, 2026 14:56:14 UTC">October 9, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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Changed the type of subtype to <code>std::uint64_t</code> in version 3.10.0.</li> <li>Fixed <a href=../dump/ ><code>dump</code></a>, <a href=../std_hash/ ><code>std::hash</code></a>, and <a href=../to_ubjson/ ><code>to_ubjson</code></a> for byte types that are not integers (e.g., <code class=highlight><span class=n>std</span><span class=o>::</span><span class=kt>byte</span></code>) in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>. <code>dump</code> now writes the bytes of a signed byte type (e.g., <code class=highlight><span class=kt>char</span></code>) as 0..255 rather than as negative numbers.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 17:25:44 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383Line truncated
+3 -3
View File
@@ -80,7 +80,7 @@ Binary Arrays are stored as pointers in a `basic_json` type. That is, for any ac
- MessagePack - MessagePack
- If a subtype is given and the binary array contains exactly 1, 2, 4, 8, or 16 elements, the fixext family (fixext1, fixext2, fixext4, fixext8) is used. For other sizes, the ext family (ext8, ext16, ext32) is used. The subtype is then added as a signed 8-bit integer. - If a subtype is given and the binary array contains exactly 1, 2, 4, 8, or 16 elements, the fixext family (fixext1, fixext2, fixext4, fixext8, fixext16) is used. For other sizes, the ext family (ext8, ext16, ext32) is used. The subtype is then written as the signed 8-bit ext type: subtypes 128 to 255 map to the negative (reserved) ext types, and on reading the ext type is exposed as an unsigned subtype from 0 to 255.
- If no subtype is given, the bin family (bin8, bin16, bin32) is used. - If no subtype is given, the bin family (bin8, bin16, bin32) is used.
- BSON - BSON
@@ -99,11 +99,11 @@ The following code shows that `binary_t` is by default, a typedef to `nlohmann::
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
std::cout << std::boolalpha << std::is_same<nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>, json::binary_t>::value << std::endl; std::cout << std::boolalpha << std::is_same<nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>, json::binary_t>::value << '\n';
} }
``` ```
+85
View File
@@ -0,0 +1,85 @@
# <small>nlohmann::basic_json::</small>bjdata_version_t
```cpp
enum class bjdata_version_t
{
draft2,
draft3
};
```
This enumeration is used in [`to_bjdata`](to_bjdata.md) to choose the version of the BJData specification to write:
draft2
: BJData Draft 2 (the default). Binary values are written as arrays of `U` integers, and ND-arrays with
`"_ArrayType_": "byte"` are written as regular objects, since the `B` marker is not part of Draft 2.
draft3
: BJData Draft 3. Binary values are written as `B` elements: as an optimized binary array (`[$B#`) if both `use_size`
and `use_type` are set, and as an array of `B`-prefixed elements otherwise. ND-arrays with
`"_ArrayType_": "byte"` are written as packed arrays (`[$B#[...]`).
Only the writer is affected by the version. [`from_bjdata`](from_bjdata.md) reads the markers of both drafts.
## Examples
??? example
The example below shows how the different values of the `bjdata_version_t` influence the serialization of a binary
value with [`to_bjdata`](to_bjdata.md).
```cpp
#include <iomanip>
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
void print_hex(const char* label, const std::vector<std::uint8_t>& v)
{
std::cout << label << ':';
for (auto b : v)
{
std::cout << ' ' << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(b);
}
std::cout << std::dec << std::setfill(' ') << '\n';
}
int main()
{
// a binary value
json j = json::binary({0xCA, 0xFE, 0xBA, 0xBE});
// Draft 2 (the default) writes an array of integers
auto v2 = json::to_bjdata(j, true, true, json::bjdata_version_t::draft2);
print_hex("draft2", v2);
// Draft 3 writes an optimized binary array
auto v3 = json::to_bjdata(j, true, true, json::bjdata_version_t::draft3);
print_hex("draft3", v3);
// reading yields an array for Draft 2 and a binary value for Draft 3
std::cout << json::from_bjdata(v2) << '\n';
std::cout << json::from_bjdata(v3) << '\n';
}
```
Output:
```json
draft2: 5b 24 55 23 69 04 ca fe ba be
draft3: 5b 24 42 23 69 04 ca fe ba be
[202,254,186,190]
{"bytes":[202,254,186,190],"subtype":null}
```
## See also
- [to_bjdata](to_bjdata.md) serializes a JSON value to BJData
- [BJData](../../features/binary_formats/bjdata.md) - the article on the BJData format
## Version history
- Added in version 3.12.0.
@@ -0,0 +1,43 @@
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<span class=p>{</span>
<span class=w> </span><span class=n>draft2</span><span class=p>,</span>
<span class=w> </span><span class=n>draft3</span>
<span class=p>};</span>
</code></pre></div> <p>This enumeration is used in <a href=../to_bjdata/ ><code>to_bjdata</code></a> to choose the version of the <abbr title="Binary JData">BJData</abbr> specification to write:</p> <dl> <dt>draft2</dt> <dd><abbr title="Binary JData">BJData</abbr> Draft 2 (the default). Binary values are written as arrays of <code>U</code> integers, and ND-arrays with <code>"_ArrayType_": "byte"</code> are written as regular objects, since the <code>B</code> marker is not part of Draft 2.</dd> <dt>draft3</dt> <dd><abbr title="Binary JData">BJData</abbr> Draft 3. Binary values are written as <code>B</code> elements: as an optimized binary array (<code>[$B#</code>) if both <code>use_size</code> and <code>use_type</code> are set, and as an array of <code>B</code>-prefixed elements otherwise. ND-arrays with <code>"_ArrayType_": "byte"</code> are written as packed arrays (<code>[$B#[...]</code>).</dd> </dl> <p>Only the writer is affected by the version. <a href=../from_bjdata/ ><code>from_bjdata</code></a> reads the markers of both drafts.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how the different values of the <code>bjdata_version_t</code> influence the serialization of a binary value with <a href=../to_bjdata/ ><code>to_bjdata</code></a>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>void</span><span class=w> </span><span class=nf>print_hex</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span><span class=w> </span><span class=n>label</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>&lt;</span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>&gt;&amp;</span><span class=w> </span><span class=n>v</span><span class=p>)</span>
<span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>label</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>':'</span><span class=p>;</span>
<span class=w> </span><span class=k>for</span><span class=w> </span><span class=p>(</span><span class=k>auto</span><span class=w> </span><span class=n>b</span><span class=w> </span><span class=o>:</span><span class=w> </span><span class=n>v</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>' '</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>hex</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>2</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setfill</span><span class=p>(</span><span class=sc>'0'</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=k>static_cast</span><span class=o>&lt;</span><span class=kt>int</span><span class=o>&gt;</span><span class=p>(</span><span class=n>b</span><span class=p>);</span>
<span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>dec</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setfill</span><span class=p>(</span><span class=sc>' '</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
<span class=w> </span><span class=c1>// a binary value</span>
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>binary</span><span class=p>({</span><span class=mh>0xCA</span><span class=p>,</span><span class=w> </span><span class=mh>0xFE</span><span class=p>,</span><span class=w> </span><span class=mh>0xBA</span><span class=p>,</span><span class=w> </span><span class=mh>0xBE</span><span class=p>});</span>
<span class=w> </span><span class=c1>// Draft 2 (the default) writes an array of integers</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>v2</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>to_bjdata</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>bjdata_version_t</span><span class=o>::</span><span class=n>draft2</span><span class=p>);</span>
<span class=w> </span><span class=n>print_hex</span><span class=p>(</span><span class=s>"draft2"</span><span class=p>,</span><span class=w> </span><span class=n>v2</span><span class=p>);</span>
<span class=w> </span><span class=c1>// Draft 3 writes an optimized binary array</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>v3</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>to_bjdata</span><span class=p>(</span><span class=n>j</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>bjdata_version_t</span><span class=o>::</span><span class=n>draft3</span><span class=p>);</span>
<span class=w> </span><span class=n>print_hex</span><span class=p>(</span><span class=s>"draft3"</span><span class=p>,</span><span class=w> </span><span class=n>v3</span><span class=p>);</span>
<span class=w> </span><span class=c1>// reading yields an array for Draft 2 and a binary value for Draft 3</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>from_bjdata</span><span class=p>(</span><span class=n>v2</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>from_bjdata</span><span class=p>(</span><span class=n>v3</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>dra</span><span class=kc>ft</span><span class=mi>2</span><span class=p>:</span><span class=w> </span><span class=mi>5</span><span class=err>b</span><span class=w> </span><span class=mi>24</span><span class=w> </span><span class=mi>55</span><span class=w> </span><span class=mi>23</span><span class=w> </span><span class=mi>69</span><span class=w> </span><span class=mi>04</span><span class=w> </span><span class=err>ca</span><span class=w> </span><span class=kc>fe</span><span class=w> </span><span class=err>ba</span><span class=w> </span><span class=err>be</span>
<span class=err>dra</span><span class=kc>ft</span><span class=mi>3</span><span class=p>:</span><span class=w> </span><span class=mi>5</span><span class=err>b</span><span class=w> </span><span class=mi>24</span><span class=w> </span><span class=mi>42</span><span class=w> </span><span class=mi>23</span><span class=w> </span><span class=mi>69</span><span class=w> </span><span class=mi>04</span><span class=w> </span><span class=err>ca</span><span class=w> </span><span class=kc>fe</span><span class=w> </span><span class=err>ba</span><span class=w> </span><span class=err>be</span>
<span class=p>[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>]</span>
<span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=kc>null</span><span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../to_bjdata/ >to_bjdata</a> serializes a <abbr title="JavaScript Object Notation">JSON</abbr> value to <abbr title="Binary JData">BJData</abbr></li> <li><a href=../../../features/binary_formats/bjdata/ ><abbr title="Binary JData">BJData</abbr></a> - the article on the <abbr title="Binary JData">BJData</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.12.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 17:25:46 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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# nlohmann::basic_json::bjdata_version_t
```
enum class bjdata_version_t
{
draft2,
draft3
};
```
This enumeration is used in [`to_bjdata`](https://json.nlohmann.me/api/basic_json/to_bjdata/index.md) to choose the version of the BJData specification to write:
draft2 : BJData Draft 2 (the default). Binary values are written as arrays of `U` integers, and ND-arrays with `"_ArrayType_": "byte"` are written as regular objects, since the `B` marker is not part of Draft 2.
draft3 : BJData Draft 3. Binary values are written as `B` elements: as an optimized binary array (`[$B#`) if both `use_size` and `use_type` are set, and as an array of `B`-prefixed elements otherwise. ND-arrays with `"_ArrayType_": "byte"` are written as packed arrays (`[$B#[...]`).
Only the writer is affected by the version. [`from_bjdata`](https://json.nlohmann.me/api/basic_json/from_bjdata/index.md) reads the markers of both drafts.
## Examples
Example
The example below shows how the different values of the `bjdata_version_t` influence the serialization of a binary value with [`to_bjdata`](https://json.nlohmann.me/api/basic_json/to_bjdata/index.md).
```
#include <iomanip>
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
void print_hex(const char* label, const std::vector<std::uint8_t>& v)
{
std::cout << label << ':';
for (auto b : v)
{
std::cout << ' ' << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(b);
}
std::cout << std::dec << std::setfill(' ') << '\n';
}
int main()
{
// a binary value
json j = json::binary({0xCA, 0xFE, 0xBA, 0xBE});
// Draft 2 (the default) writes an array of integers
auto v2 = json::to_bjdata(j, true, true, json::bjdata_version_t::draft2);
print_hex("draft2", v2);
// Draft 3 writes an optimized binary array
auto v3 = json::to_bjdata(j, true, true, json::bjdata_version_t::draft3);
print_hex("draft3", v3);
// reading yields an array for Draft 2 and a binary value for Draft 3
std::cout << json::from_bjdata(v2) << '\n';
std::cout << json::from_bjdata(v3) << '\n';
}
```
Output:
```
draft2: 5b 24 55 23 69 04 ca fe ba be
draft3: 5b 24 42 23 69 04 ca fe ba be
[202,254,186,190]
{"bytes":[202,254,186,190],"subtype":null}
```
## See also
- [to_bjdata](https://json.nlohmann.me/api/basic_json/to_bjdata/index.md) serializes a JSON value to BJData
- [BJData](https://json.nlohmann.me/features/binary_formats/bjdata/index.md) - the article on the BJData format
## Version history
- Added in version 3.12.0.
+2 -2
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@@ -40,11 +40,11 @@ Boolean values are stored directly inside a `basic_json` type.
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
std::cout << std::boolalpha << std::is_same<bool, json::boolean_t>::value << std::endl; std::cout << std::boolalpha << std::is_same<bool, json::boolean_t>::value << '\n';
} }
``` ```
+3 -3
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@@ -1,13 +1,13 @@
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</code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> booleans.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code class=highlight><span class=kc>true</span></code> and <code class=highlight><span class=kc>false</span></code>.</p> <p>To store boolean values in C++, a type is defined by the template parameter <code>BooleanType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BooleanType</code></dt> <dd>the type to store booleans. As it is stored directly inside a <code>basic_json</code> value (in a union), it must be a trivially default-constructible, trivially copyable, and trivially destructible type that is convertible to and from <code class=highlight><span class=kt>bool</span></code>. See <a href=../../../features/types/template_parameters/#booleantype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>With the default values for <code>BooleanType</code> (<code class=highlight><span class=kt>bool</span></code>), the default type for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">&para;</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>boolean_t</code> is by default, a typedef to <code class=highlight><span class=kt>bool</span></code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>The type used to store <abbr title="JavaScript Object Notation">JSON</abbr> booleans.</p> <p><a href="https://tools.ietf.org/html/rfc8259"><abbr title="Request for Comments">RFC</abbr> 8259</a> implicitly describes a boolean as a type which differentiates the two literals <code class=highlight><span class=kc>true</span></code> and <code class=highlight><span class=kc>false</span></code>.</p> <p>To store boolean values in C++, a type is defined by the template parameter <code>BooleanType</code> which chooses the type to use.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BooleanType</code></dt> <dd>the type to store booleans. As it is stored directly inside a <code>basic_json</code> value (in a union), it must be a trivially default-constructible, trivially copyable, and trivially destructible type that is convertible to and from <code class=highlight><span class=kt>bool</span></code>. See <a href=../../../features/types/template_parameters/#booleantype>Template Parameter Requirements</a>.</dd> </dl> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <h3 id=default-type>Default type<a class=headerlink href=#default-type title="Permanent link">&para;</a></h3> <p>With the default values for <code>BooleanType</code> (<code class=highlight><span class=kt>bool</span></code>), the default type for <code>boolean_t</code> is <code class=highlight><span class=kt>bool</span></code>.</p> <h3 id=storage>Storage<a class=headerlink href=#storage title="Permanent link">&para;</a></h3> <p>Boolean values are stored directly inside a <code>basic_json</code> type.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows that <code>boolean_t</code> is by default, a typedef to <code class=highlight><span class=kt>bool</span></code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o>&lt;</span><span class=kt>bool</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>boolean_t</span><span class=o>&gt;::</span><span class=n>value</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>is_same</span><span class=o>&lt;</span><span class=kt>bool</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>boolean_t</span><span class=o>&gt;::</span><span class=n>value</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../is_boolean/ >is_boolean</a> checks whether the <abbr title="JavaScript Object Notation">JSON</abbr> value is a boolean</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 1.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 14, 2026 16:28:49 UTC">October 14, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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+2 -2
View File
@@ -35,11 +35,11 @@ The following code shows that `boolean_t` is by default, a typedef to `bool`.
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
std::cout << std::boolalpha << std::is_same<bool, json::boolean_t>::value << std::endl; std::cout << std::boolalpha << std::is_same<bool, json::boolean_t>::value << '\n';
} }
``` ```
+1 -1
View File
@@ -30,7 +30,7 @@ Constant.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
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@@ -1,8 +1,8 @@
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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/cbegin/" rel="canonical"><link href=../boolean_t/ rel=prev><link href=../cbor_tag_handler_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>cbegin - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> cbegin </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo 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</code></pre></div> <p>Returns an iterator to the first element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cbegin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Returns an iterator to the first element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator to the first element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cbegin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
View File
@@ -28,7 +28,7 @@ The following code shows an example for `cbegin()`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+8 -6
View File
@@ -15,11 +15,13 @@ error
: report a parse error in case of a tag (the `from_cbor` overloads throw a `parse_error` exception by default) : report a parse error in case of a tag (the `from_cbor` overloads throw a `parse_error` exception by default)
ignore ignore
: ignore tags : ignore tags (also in front of a text string map key)
store store
: store tagged byte strings (for bytes 0xd8..0xdb) as binary values with the tag as subtype; other tagged values are : store tagged byte strings (for bytes 0xd8..0xdb) as binary values with the tag as subtype; other tagged values are
read as if the tag were ignored. If several tags precede a byte string, only the innermost one is stored. read as if the tag were ignored. If several tags precede a byte string, only the tag directly in front of it is
stored, and only when it has the form 0xd8..0xdb (a tag 0..23 written as 0xc0..0xd7 is skipped). Tags in front of a
text string map key are skipped.
## Examples ## Examples
@@ -32,7 +34,7 @@ store
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -46,16 +48,16 @@ store
} }
catch (const json::parse_error& e) catch (const json::parse_error& e)
{ {
std::cout << e.what() << std::endl; std::cout << e.what() << '\n';
} }
// cbor_tag_handler_t::ignore ignores the tag // cbor_tag_handler_t::ignore ignores the tag
auto b_ignore_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::ignore); auto b_ignore_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::ignore);
std::cout << b_ignore_tag << std::endl; std::cout << b_ignore_tag << '\n';
// cbor_tag_handler_t::store stores the tag as binary subtype // cbor_tag_handler_t::store stores the tag as binary subtype
auto b_store_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::store); auto b_store_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::store);
std::cout << b_store_tag << std::endl; std::cout << b_store_tag << '\n';
} }
``` ```
+7 -7
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@@ -1,13 +1,13 @@
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<span class=p>{</span> <span class=p>{</span>
<span class=w> </span><span class=n>error</span><span class=p>,</span> <span class=w> </span><span class=n>error</span><span class=p>,</span>
<span class=w> </span><span class=n>ignore</span><span class=p>,</span> <span class=w> </span><span class=n>ignore</span><span class=p>,</span>
<span class=w> </span><span class=n>store</span> <span class=w> </span><span class=n>store</span>
<span class=p>};</span> <span class=p>};</span>
</code></pre></div> <p>This enumeration is used in <a href=../from_cbor/ ><code>from_cbor</code></a> and <a href=../sax_parse/ ><code>sax_parse</code></a> to choose how to treat tags:</p> <dl> <dt>error</dt> <dd>report a parse error in case of a tag (the <code>from_cbor</code> overloads throw a <code>parse_error</code> exception by default)</dd> <dt>ignore</dt> <dd>ignore tags</dd> <dt>store</dt> <dd>store tagged byte strings (for bytes 0xd8..0xdb) as binary values with the tag as subtype; other tagged values are read as if the tag were ignored. If several tags precede a byte string, only the innermost one is stored.</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how the different values of the <code>cbor_tag_handler_t</code> influence the behavior of <a href=../from_cbor/ ><code>from_cbor</code></a> when reading a tagged byte string.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>This enumeration is used in <a href=../from_cbor/ ><code>from_cbor</code></a> and <a href=../sax_parse/ ><code>sax_parse</code></a> to choose how to treat tags:</p> <dl> <dt>error</dt> <dd>report a parse error in case of a tag (the <code>from_cbor</code> overloads throw a <code>parse_error</code> exception by default)</dd> <dt>ignore</dt> <dd>ignore tags (also in front of a text string map key)</dd> <dt>store</dt> <dd>store tagged byte strings (for bytes 0xd8..0xdb) as binary values with the tag as subtype; other tagged values are read as if the tag were ignored. If several tags precede a byte string, only the tag directly in front of it is stored, and only when it has the form 0xd8..0xdb (a tag 0..23 written as 0xc0..0xd7 is skipped). Tags in front of a text string map key are skipped.</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how the different values of the <code>cbor_tag_handler_t</code> influence the behavior of <a href=../from_cbor/ ><code>from_cbor</code></a> when reading a tagged byte string.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -21,18 +21,18 @@
<span class=w> </span><span class=p>}</span> <span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse_error</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span> <span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>parse_error</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span> <span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span> <span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=c1>// cbor_tag_handler_t::ignore ignores the tag</span> <span class=w> </span><span class=c1>// cbor_tag_handler_t::ignore ignores the tag</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>b_ignore_tag</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>from_cbor</span><span class=p>(</span><span class=n>vec</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>cbor_tag_handler_t</span><span class=o>::</span><span class=n>ignore</span><span class=p>);</span> <span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>b_ignore_tag</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>from_cbor</span><span class=p>(</span><span class=n>vec</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>cbor_tag_handler_t</span><span class=o>::</span><span class=n>ignore</span><span class=p>);</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>b_ignore_tag</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>b_ignore_tag</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=c1>// cbor_tag_handler_t::store stores the tag as binary subtype</span> <span class=w> </span><span class=c1>// cbor_tag_handler_t::store stores the tag as binary subtype</span>
<span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>b_store_tag</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>from_cbor</span><span class=p>(</span><span class=n>vec</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>cbor_tag_handler_t</span><span class=o>::</span><span class=n>store</span><span class=p>);</span> <span class=w> </span><span class=k>auto</span><span class=w> </span><span class=n>b_store_tag</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>from_cbor</span><span class=p>(</span><span class=n>vec</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=nb>true</span><span class=p>,</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>cbor_tag_handler_t</span><span class=o>::</span><span class=n>store</span><span class=p>);</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>b_store_tag</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>b_store_tag</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.parse_error.</span><span class=mi>112</span><span class=p>]</span><span class=w> </span><span class=err>parse</span><span class=w> </span><span class=err>error</span><span class=w> </span><span class=err>a</span><span class=kc>t</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=w> </span><span class=mi>1</span><span class=p>:</span><span class=w> </span><span class=err>sy</span><span class=kc>nta</span><span class=err>x</span><span class=w> </span><span class=err>error</span><span class=w> </span><span class=err>while</span><span class=w> </span><span class=err>parsi</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>CBOR</span><span class=w> </span><span class=err>value</span><span class=p>:</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=p>:</span><span class=w> </span><span class=mi>0</span><span class=err>xD</span><span class=mi>8</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.parse_error.</span><span class=mi>112</span><span class=p>]</span><span class=w> </span><span class=err>parse</span><span class=w> </span><span class=err>error</span><span class=w> </span><span class=err>a</span><span class=kc>t</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=w> </span><span class=mi>1</span><span class=p>:</span><span class=w> </span><span class=err>sy</span><span class=kc>nta</span><span class=err>x</span><span class=w> </span><span class=err>error</span><span class=w> </span><span class=err>while</span><span class=w> </span><span class=err>parsi</span><span class=kc>n</span><span class=err>g</span><span class=w> </span><span class=err>CBOR</span><span class=w> </span><span class=err>value</span><span class=p>:</span><span class=w> </span><span class=err>i</span><span class=kc>n</span><span class=err>valid</span><span class=w> </span><span class=err>by</span><span class=kc>te</span><span class=p>:</span><span class=w> </span><span class=mi>0</span><span class=err>xD</span><span class=mi>8</span>
<span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=kc>null</span><span class=p>}</span> <span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=kc>null</span><span class=p>}</span>
<span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=mi>66</span><span class=p>}</span> <span class=p>{</span><span class=nt>"bytes"</span><span class=p>:[</span><span class=mi>202</span><span class=p>,</span><span class=mi>254</span><span class=p>,</span><span class=mi>186</span><span class=p>,</span><span class=mi>190</span><span class=p>],</span><span class=nt>"subtype"</span><span class=p>:</span><span class=mi>66</span><span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../from_cbor/ >from_cbor</a> deserializes a <abbr title="JavaScript Object Notation">JSON</abbr> value from <abbr title="Concise Binary Object Representation">CBOR</abbr></li> <li><a href=../input_format_t/ >input_format_t</a> the enumeration of supported input formats</li> <li><a href=../../../features/binary_formats/cbor/ ><abbr title="Concise Binary Object Representation">CBOR</abbr></a> - the article on the <abbr title="Concise Binary Object Representation">CBOR</abbr> format</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.9.0. 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Added value <code>store</code> in 3.10.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 17:25:44 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M416 32H31.9C14.3 32 0 46.5 0 64.3v383.4C0 465.5 14.3 480 31.9 480H416c17.6 0 32-14.5 32-32.3V64.3c0-17.8-14.4-32.3-32-32.3M135.4 416H69V202.2h66.5V416zM102.2 96a38.5 38.5 0 1 1 0 77 38.5 38.5 0 1 1 0-77m282.1 320h-66.4V312c0-24.8-.5-56.7-34.5-56.7-34.6 0-39.9 27-3Line truncated
+6 -6
View File
@@ -13,9 +13,9 @@ This enumeration is used in [`from_cbor`](https://json.nlohmann.me/api/basic_jso
error : report a parse error in case of a tag (the `from_cbor` overloads throw a `parse_error` exception by default) error : report a parse error in case of a tag (the `from_cbor` overloads throw a `parse_error` exception by default)
ignore : ignore tags ignore : ignore tags (also in front of a text string map key)
store : store tagged byte strings (for bytes 0xd8..0xdb) as binary values with the tag as subtype; other tagged values are read as if the tag were ignored. If several tags precede a byte string, only the innermost one is stored. store : store tagged byte strings (for bytes 0xd8..0xdb) as binary values with the tag as subtype; other tagged values are read as if the tag were ignored. If several tags precede a byte string, only the tag directly in front of it is stored, and only when it has the form 0xd8..0xdb (a tag 0..23 written as 0xc0..0xd7 is skipped). Tags in front of a text string map key are skipped.
## Examples ## Examples
@@ -27,7 +27,7 @@ The example below shows how the different values of the `cbor_tag_handler_t` inf
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -41,16 +41,16 @@ int main()
} }
catch (const json::parse_error& e) catch (const json::parse_error& e)
{ {
std::cout << e.what() << std::endl; std::cout << e.what() << '\n';
} }
// cbor_tag_handler_t::ignore ignores the tag // cbor_tag_handler_t::ignore ignores the tag
auto b_ignore_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::ignore); auto b_ignore_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::ignore);
std::cout << b_ignore_tag << std::endl; std::cout << b_ignore_tag << '\n';
// cbor_tag_handler_t::store stores the tag as binary subtype // cbor_tag_handler_t::store stores the tag as binary subtype
auto b_store_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::store); auto b_store_tag = json::from_cbor(vec, true, true, json::cbor_tag_handler_t::store);
std::cout << b_store_tag << std::endl; std::cout << b_store_tag << '\n';
} }
``` ```
+1 -1
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@@ -30,7 +30,7 @@ Constant.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
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@@ -1,8 +1,8 @@
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</code></pre></div> <p>Returns an iterator to one past the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cend()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Returns an iterator to one past the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>cend()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
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@@ -28,7 +28,7 @@ The following code shows an example for `cend()`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+1 -1
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@@ -46,7 +46,7 @@ All iterators, pointers, and references related to this container are invalidate
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
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@@ -1,9 +1,9 @@
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1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div Line truncated
</code></pre></div> <p>Clears the content of a <abbr title="JavaScript Object Notation">JSON</abbr> value and resets it to the default value as if <a href=../basic_json/ ><code>basic_json(value_t)</code></a> would have been called with the current value type from <a href=../type/ ><code>type()</code></a>:</p> <table> <thead> <tr> <th>Value type</th> <th>initial value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code>null</code></td> </tr> <tr> <td>boolean</td> <td><code>false</code></td> </tr> <tr> <td>string</td> <td><code>""</code></td> </tr> <tr> <td>number</td> <td><code>0</code></td> </tr> <tr> <td>binary</td> <td>An empty byte vector with no subtype</td> </tr> <tr> <td>object</td> <td><code>{}</code></td> </tr> <tr> <td>array</td> <td><code>[]</code></td> </tr> </tbody> </table> <p>Has the same effect as calling</p> <div class=highlight><pre><span></span><code><span class=o>*</span><span class=k>this</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>basic_json</span><span class=p>(</span><span class=n>type</span><span class=p>());</span> </code></pre></div> <p>Clears the content of a <abbr title="JavaScript Object Notation">JSON</abbr> value and resets it to the default value as if <a href=../basic_json/ ><code>basic_json(value_t)</code></a> would have been called with the current value type from <a href=../type/ ><code>type()</code></a>:</p> <table> <thead> <tr> <th>Value type</th> <th>initial value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code>null</code></td> </tr> <tr> <td>boolean</td> <td><code>false</code></td> </tr> <tr> <td>string</td> <td><code>""</code></td> </tr> <tr> <td>number</td> <td><code>0</code></td> </tr> <tr> <td>binary</td> <td>An empty byte vector with no subtype</td> </tr> <tr> <td>object</td> <td><code>{}</code></td> </tr> <tr> <td>array</td> <td><code>[]</code></td> </tr> </tbody> </table> <p>Has the same effect as calling</p> <div class=highlight><pre><span></span><code><span class=o>*</span><span class=k>this</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>basic_json</span><span class=p>(</span><span class=n>type</span><span class=p>());</span>
</code></pre></div> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>All iterators, pointers, and references related to this container are invalidated.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows the effect of <code>clear()</code> to different <abbr title="JavaScript Object Notation">JSON</abbr> types.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>All iterators, pointers, and references related to this container are invalidated.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows the effect of <code>clear()</code> to different <abbr title="JavaScript Object Notation">JSON</abbr> types.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
View File
@@ -44,7 +44,7 @@ The example below shows the effect of `clear()` to different JSON types.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+15 -8
View File
@@ -61,11 +61,18 @@ Strong exception safety: if an exception occurs, the original value stays intact
## Complexity ## Complexity
Logarithmic in the size of the JSON object. 1. Logarithmic in the size of the JSON object.
2. Logarithmic in the size of the JSON object.
3. At most one lookup per reference token of `ptr`, each logarithmic in the size of the container at that level:
O(*n* log *m*) for *n* reference tokens and containers of size at most *m*.
4. Deleted; a call with an integral argument does not compile.
## Notes ## Notes
- This method always returns `#!cpp false` when executed on a JSON type that is not an object. - Overloads (1) and (2) always return `#!cpp false` when executed on a JSON type that is not an object. Overload (3)
also works on arrays and on primitive values: the empty JSON pointer resolves in every JSON value (so
`#!cpp json(1).contains(""_json_pointer)` returns `#!cpp true`), and `#!cpp json({1, 2}).contains("/1"_json_pointer)`
returns `#!cpp true`.
- This method can be executed on any JSON value type. - This method can be executed on any JSON value type.
- Calling this function with an integer argument (for example, `#!cpp contains(0)`) does not compile: such an argument - Calling this function with an integer argument (for example, `#!cpp contains(0)`) does not compile: such an argument
would otherwise implicitly convert to a null `#!cpp const char*` and, from there, cause undefined behavior when would otherwise implicitly convert to a null `#!cpp const char*` and, from there, cause undefined behavior when
@@ -98,7 +105,7 @@ Logarithmic in the size of the JSON object.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -111,7 +118,7 @@ Logarithmic in the size of the JSON object.
std::cout << std::boolalpha << std::cout << std::boolalpha <<
"j_object contains 'key': " << j_object.contains("key") << '\n' << "j_object contains 'key': " << j_object.contains("key") << '\n' <<
"j_object contains 'another': " << j_object.contains("another") << '\n' << "j_object contains 'another': " << j_object.contains("another") << '\n' <<
"j_array contains 'key': " << j_array.contains("key") << std::endl; "j_array contains 'key': " << j_array.contains("key") << '\n';
} }
``` ```
@@ -135,7 +142,7 @@ Logarithmic in the size of the JSON object.
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -148,7 +155,7 @@ Logarithmic in the size of the JSON object.
std::cout << std::boolalpha << std::cout << std::boolalpha <<
"j_object contains 'key': " << j_object.contains("key"sv) << '\n' << "j_object contains 'key': " << j_object.contains("key"sv) << '\n' <<
"j_object contains 'another': " << j_object.contains("another"sv) << '\n' << "j_object contains 'another': " << j_object.contains("another"sv) << '\n' <<
"j_array contains 'key': " << j_array.contains("key"sv) << std::endl; "j_array contains 'key': " << j_array.contains("key"sv) << '\n';
} }
``` ```
@@ -170,7 +177,7 @@ Logarithmic in the size of the JSON object.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -192,7 +199,7 @@ Logarithmic in the size of the JSON object.
// an array index with a leading '0' is not found // an array index with a leading '0' is not found
<< j.contains("/array/01"_json_pointer) << '\n' << j.contains("/array/01"_json_pointer) << '\n'
// an array index that is not a number is not found // an array index that is not a number is not found
<< j.contains("/array/one"_json_pointer) << std::endl; << j.contains("/array/one"_json_pointer) << '\n';
} }
``` ```
+9 -9
View File
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/contains/" rel="canonical"><link href=../clear/ rel=prev><link href=../count/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>contains - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </laLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/contains/" rel="canonical"><link href=../clear/ rel=prev><link href=../count/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>contains - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=kt>bool</span><span class=w> </span><span class=nf>contains</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span> <span class=kt>bool</span><span class=w> </span><span class=nf>contains</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
<span class=c1>// (2)</span> <span class=c1>// (2)</span>
@@ -11,10 +11,10 @@
<span class=c1>// (4)</span> <span class=c1>// (4)</span>
<span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=o>&gt;</span> <span class=k>template</span><span class=o>&lt;</span><span class=k>typename</span><span class=w> </span><span class=nc>T</span><span class=o>&gt;</span>
<span class=kt>bool</span><span class=w> </span><span class=n>contains</span><span class=p>(</span><span class=n>T</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>delete</span><span class=p>;</span> <span class=kt>bool</span><span class=w> </span><span class=n>contains</span><span class=p>(</span><span class=n>T</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>delete</span><span class=p>;</span>
</code></pre></div> <ol> <li>Check whether an element exists in a <abbr title="JavaScript Object Notation">JSON</abbr> object with a key equivalent to <code>key</code>. If the element is not found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code class=highlight><span class=nb>false</span></code> is returned.</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Check whether the given <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> can be resolved in the current <abbr title="JavaScript Object Notation">JSON</abbr> value.</li> <li>Deleted: this overload is only available if <code>T</code> is an integral type and is declared as deleted, so that a call with an integer <code>key</code> (for example, <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) fails to compile. Otherwise, the integer literal <code>0</code> would convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, to the key type, causing undefined behavior at runtime.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value to check its existence.</dd> <dt><code>ptr</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> pointer to check its existence.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li><code class=highlight><span class=nb>true</span></code> if an element with specified <code>key</code> exists. If no such element with such a key is found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code class=highlight><span class=nb>false</span></code> is returned.</li> <li>See 1.</li> <li><code class=highlight><span class=nb>true</span></code> if the <abbr title="JavaScript Object Notation">JSON</abbr> pointer can be resolved to a stored value, <code class=highlight><span class=nb>false</span></code> otherwise.</li> <li>Deleted; a call with an integral argument does not compile.</li> </ol> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <ol> <li>The function does not throw exceptions.</li> <li>The function does not throw exceptions.</li> <li>The function does not throw exceptions.</li> <li>Deleted; a call with an integral argument does not compile.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>This method always returns <code class=highlight><span class=nb>false</span></code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>This method can be executed on any <abbr title="JavaScript Object Notation">JSON</abbr> value type.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>contains</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To check for an array element instead, use <a href=../at/ ><code>at</code></a>, <aLine truncated </code></pre></div> <ol> <li>Check whether an element exists in a <abbr title="JavaScript Object Notation">JSON</abbr> object with a key equivalent to <code>key</code>. If the element is not found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code class=highlight><span class=nb>false</span></code> is returned.</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Check whether the given <abbr title="JavaScript Object Notation">JSON</abbr> pointer <code>ptr</code> can be resolved in the current <abbr title="JavaScript Object Notation">JSON</abbr> value.</li> <li>Deleted: this overload is only available if <code>T</code> is an integral type and is declared as deleted, so that a call with an integer <code>key</code> (for example, <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) fails to compile. Otherwise, the integer literal <code>0</code> would convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, to the key type, causing undefined behavior at runtime.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value to check its existence.</dd> <dt><code>ptr</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> pointer to check its existence.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li><code class=highlight><span class=nb>true</span></code> if an element with specified <code>key</code> exists. If no such element with such a key is found or the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, <code class=highlight><span class=nb>false</span></code> is returned.</li> <li>See 1.</li> <li><code class=highlight><span class=nb>true</span></code> if the <abbr title="JavaScript Object Notation">JSON</abbr> pointer can be resolved to a stored value, <code class=highlight><span class=nb>false</span></code> otherwise.</li> <li>Deleted; a call with an integral argument does not compile.</li> </ol> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <ol> <li>The function does not throw exceptions.</li> <li>The function does not throw exceptions.</li> <li>The function does not throw exceptions.</li> <li>Deleted; a call with an integral argument does not compile.</li> </ol> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <ol> <li>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</li> <li>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</li> <li>At most one lookup per reference token of <code>ptr</code>, each logarithmic in the size of the container at that level: O(<em>n</em> log <em>m</em>) for <em>n</em> reference tokens and containers of size at most <em>m</em>.</li> <li>Deleted; a call with an integral argument does not compile.</li> </ol> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>Overloads (1) and (2) always return <code class=highlight><span class=nb>false</span></code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object. Overload (3) also works on arrays and on primitive values: the empty <abbr title="JavaScript Object Notation">JSON</abbr> pointer resolves in every <abbr title="JavaScript Object Notation">JSON</abbr> value (so <code class=highlight><span class=n>json</span><span class=p>(</span><span class=mi>1</span><span class=p>).</span><span class=n>contains</spanLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
@@ -27,7 +27,7 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span>
<span class=w> </span><span class=s>"j_object contains 'key': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"key"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=w> </span><span class=o>&lt;&lt;</span> <span class=w> </span><span class=s>"j_object contains 'key': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"key"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=w> </span><span class=o>&lt;&lt;</span>
<span class=w> </span><span class=s>"j_object contains 'another': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"another"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=w> </span><span class=o>&lt;&lt;</span> <span class=w> </span><span class=s>"j_object contains 'another': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"another"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=w> </span><span class=o>&lt;&lt;</span>
<span class=w> </span><span class=s>"j_array contains 'key': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_array</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"key"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=s>"j_array contains 'key': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_array</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"key"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>j_objec</span><span class=kc>t</span><span class=w> </span><span class=err>co</span><span class=kc>nta</span><span class=err>i</span><span class=kc>ns</span><span class=w> </span><span class=err>'key'</span><span class=p>:</span><span class=w> </span><span class=kc>true</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>j_objec</span><span class=kc>t</span><span class=w> </span><span class=err>co</span><span class=kc>nta</span><span class=err>i</span><span class=kc>ns</span><span class=w> </span><span class=err>'key'</span><span class=p>:</span><span class=w> </span><span class=kc>true</span>
<span class=err>j_objec</span><span class=kc>t</span><span class=w> </span><span class=err>co</span><span class=kc>nta</span><span class=err>i</span><span class=kc>ns</span><span class=w> </span><span class=err>'a</span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=err>her'</span><span class=p>:</span><span class=w> </span><span class=kc>false</span> <span class=err>j_objec</span><span class=kc>t</span><span class=w> </span><span class=err>co</span><span class=kc>nta</span><span class=err>i</span><span class=kc>ns</span><span class=w> </span><span class=err>'a</span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=err>her'</span><span class=p>:</span><span class=w> </span><span class=kc>false</span>
@@ -37,7 +37,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
@@ -50,7 +50,7 @@
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span><span class=w> </span><span class=o>&lt;&lt;</span>
<span class=w> </span><span class=s>"j_object contains 'key': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"key"</span><span class=n>sv</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=w> </span><span class=o>&lt;&lt;</span> <span class=w> </span><span class=s>"j_object contains 'key': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"key"</span><span class=n>sv</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=w> </span><span class=o>&lt;&lt;</span>
<span class=w> </span><span class=s>"j_object contains 'another': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"another"</span><span class=n>sv</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=w> </span><span class=o>&lt;&lt;</span> <span class=w> </span><span class=s>"j_object contains 'another': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_object</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"another"</span><span class=n>sv</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=w> </span><span class=o>&lt;&lt;</span>
<span class=w> </span><span class=s>"j_array contains 'key': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_array</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"key"</span><span class=n>sv</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=s>"j_array contains 'key': "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_array</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"key"</span><span class=n>sv</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>j_objec</span><span class=kc>t</span><span class=w> </span><span class=err>co</span><span class=kc>nta</span><span class=err>i</span><span class=kc>ns</span><span class=w> </span><span class=err>'key'</span><span class=p>:</span><span class=w> </span><span class=kc>true</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>j_objec</span><span class=kc>t</span><span class=w> </span><span class=err>co</span><span class=kc>nta</span><span class=err>i</span><span class=kc>ns</span><span class=w> </span><span class=err>'key'</span><span class=p>:</span><span class=w> </span><span class=kc>true</span>
<span class=err>j_objec</span><span class=kc>t</span><span class=w> </span><span class=err>co</span><span class=kc>nta</span><span class=err>i</span><span class=kc>ns</span><span class=w> </span><span class=err>'a</span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=err>her'</span><span class=p>:</span><span class=w> </span><span class=kc>false</span> <span class=err>j_objec</span><span class=kc>t</span><span class=w> </span><span class=err>co</span><span class=kc>nta</span><span class=err>i</span><span class=kc>ns</span><span class=w> </span><span class=err>'a</span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=err>her'</span><span class=p>:</span><span class=w> </span><span class=kc>false</span>
@@ -58,7 +58,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (3) check with <abbr title="JavaScript Object Notation">JSON</abbr> pointer</summary> <p>The example shows how <code>contains()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (3) check with <abbr title="JavaScript Object Notation">JSON</abbr> pointer</summary> <p>The example shows how <code>contains()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
@@ -80,7 +80,7 @@
<span class=w> </span><span class=c1>// an array index with a leading '0' is not found</span> <span class=w> </span><span class=c1>// an array index with a leading '0' is not found</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"/array/01"</span><span class=n>_json_pointer</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span> <span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"/array/01"</span><span class=n>_json_pointer</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span>
<span class=w> </span><span class=c1>// an array index that is not a number is not found</span> <span class=w> </span><span class=c1>// an array index that is not a number is not found</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"/array/one"</span><span class=n>_json_pointer</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j</span><span class=p>.</span><span class=n>contains</span><span class=p>(</span><span class=s>"/array/one"</span><span class=n>_json_pointer</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
<span class=kc>true</span> <span class=kc>true</span>
@@ -91,4 +91,4 @@
<span class=kc>false</span> <span class=kc>false</span>
<span class=kc>false</span> <span class=kc>false</span>
<span class=kc>false</span> <span class=kc>false</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../find/ >find</a> find a value in an object</li> <li><a href=../count/ >count</a> returns the number of occurrences of a key</li> <li><a href=../../basic_json_view/contains/ >basic_json_view::contains</a> - the same check on a zero-copy view</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 3.6.0. Extended template <code>KeyType</code> to support comparable types in version 3.11.0. Support for keys convertible to <code>std::string_view</code> added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, consistently across the lookup functions.</li> <li>Added in version 3.7.0.</li> <li>Deleted overloads for integral key types added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 24, 2026 15:57:44 UTC">October 24, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontaweLine truncated </code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../find/ >find</a> find a value in an object</li> <li><a href=../count/ >count</a> returns the number of occurrences of a key</li> <li><a href=../../basic_json_view/contains/ >basic_json_view::contains</a> - the same check on a zero-copy view</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ol> <li>Added in version 3.11.0.</li> <li>Added in version 3.6.0. Extended template <code>KeyType</code> to support comparable types in version 3.11.0. Support for keys convertible to <code>std::string_view</code> added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span>, consistently across the lookup functions.</li> <li>Added in version 3.7.0.</li> <li>Deleted overloads for integral key types added in version 3.13.0 <span class=unreleased-version title="Not part of a release yet; the latest release is 3.12.0.">unreleased</span> to reject such calls at compile time instead of causing undefined behavior at runtime.</li> </ol> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 26, 2026 16:11:46 UTC">October 26, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2025 Fonticons, Inc.--><path d="M173.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6m-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3m44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9M252.8 8C114.1 8 8 113.3 8 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C436.2 457.8 504 362.9 504 252 504 113.3 391.5 8 252.8 8M105.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1m-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7m32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1m-11.4-14.7c-1.6 1-1.6 3.6 0 5.9s4.3 3.3 5.6 2.3c1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2"/></svg> </a> <a href="https://www.linkedin.com/in/nielslohmann/" target="_blank" rel="noopener" title="www.linkedin.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 448 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - https://fontawesome.com License - https://fontaweLine truncated
+11 -8
View File
@@ -51,11 +51,14 @@ Strong exception safety: if an exception occurs, the original value stays intact
## Complexity ## Complexity
Logarithmic in the size of the JSON object. 1. Logarithmic in the size of the JSON object.
1. Logarithmic in the size of the JSON object.
1. At most one lookup per reference token of `ptr`, each logarithmic in the size of the container at that level: O(*n* log *m*) for *n* reference tokens and containers of size at most *m*.
1. Deleted; a call with an integral argument does not compile.
## Notes ## Notes
- This method always returns `false` when executed on a JSON type that is not an object. - Overloads (1) and (2) always return `false` when executed on a JSON type that is not an object. Overload (3) also works on arrays and on primitive values: the empty JSON pointer resolves in every JSON value (so `json(1).contains(""_json_pointer)` returns `true`), and `json({1, 2}).contains("/1"_json_pointer)` returns `true`.
- This method can be executed on any JSON value type. - This method can be executed on any JSON value type.
- Calling this function with an integer argument (for example, `contains(0)`) does not compile: such an argument would otherwise implicitly convert to a null `const char*` and, from there, cause undefined behavior when constructing a `std::string` for the object key. To check for an array element instead, use [`at`](https://json.nlohmann.me/api/basic_json/at/index.md), [`operator[]`](https://json.nlohmann.me/api/basic_json/operator%5B%5D/index.md), or compare against [`size`](https://json.nlohmann.me/api/basic_json/size/index.md). - Calling this function with an integer argument (for example, `contains(0)`) does not compile: such an argument would otherwise implicitly convert to a null `const char*` and, from there, cause undefined behavior when constructing a `std::string` for the object key. To check for an array element instead, use [`at`](https://json.nlohmann.me/api/basic_json/at/index.md), [`operator[]`](https://json.nlohmann.me/api/basic_json/operator%5B%5D/index.md), or compare against [`size`](https://json.nlohmann.me/api/basic_json/size/index.md).
@@ -81,7 +84,7 @@ The example shows how `contains()` is used.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -94,7 +97,7 @@ int main()
std::cout << std::boolalpha << std::cout << std::boolalpha <<
"j_object contains 'key': " << j_object.contains("key") << '\n' << "j_object contains 'key': " << j_object.contains("key") << '\n' <<
"j_object contains 'another': " << j_object.contains("another") << '\n' << "j_object contains 'another': " << j_object.contains("another") << '\n' <<
"j_array contains 'key': " << j_array.contains("key") << std::endl; "j_array contains 'key': " << j_array.contains("key") << '\n';
} }
``` ```
@@ -116,7 +119,7 @@ The example shows how `contains()` is used.
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -129,7 +132,7 @@ int main()
std::cout << std::boolalpha << std::cout << std::boolalpha <<
"j_object contains 'key': " << j_object.contains("key"sv) << '\n' << "j_object contains 'key': " << j_object.contains("key"sv) << '\n' <<
"j_object contains 'another': " << j_object.contains("another"sv) << '\n' << "j_object contains 'another': " << j_object.contains("another"sv) << '\n' <<
"j_array contains 'key': " << j_array.contains("key"sv) << std::endl; "j_array contains 'key': " << j_array.contains("key"sv) << '\n';
} }
``` ```
@@ -149,7 +152,7 @@ The example shows how `contains()` is used.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -171,7 +174,7 @@ int main()
// an array index with a leading '0' is not found // an array index with a leading '0' is not found
<< j.contains("/array/01"_json_pointer) << '\n' << j.contains("/array/01"_json_pointer) << '\n'
// an array index that is not a number is not found // an array index that is not a number is not found
<< j.contains("/array/one"_json_pointer) << std::endl; << j.contains("/array/one"_json_pointer) << '\n';
} }
``` ```
+2 -2
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@@ -63,7 +63,7 @@ Logarithmic in the size of the JSON object.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -99,7 +99,7 @@ Logarithmic in the size of the JSON object.
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+3 -3
View File
@@ -1,4 +1,4 @@
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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <dLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/count/" rel="canonical"><link href=../contains/ rel=prev><link href=../crbegin/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>count - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=n>size_type</span><span class=w> </span><span class=nf>count</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span> <span class=n>size_type</span><span class=w> </span><span class=nf>count</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span><span class=o>&amp;</span><span class=w> </span><span class=n>key</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
<span class=c1>// (2)</span> <span class=c1>// (2)</span>
@@ -11,7 +11,7 @@
</code></pre></div> <ol> <li>Returns the number of elements with key <code>key</code>. If <code>ObjectType</code> is the default <code>std::map</code> type, the return value will always be <code>0</code> (<code>key</code> was not found) or <code>1</code> (<code>key</code> was found).</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Deleted: this overload is only available if <code>T</code> is an integral type and is declared as deleted, so that a call with an integer <code>key</code> (for example, <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>count</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) fails to compile. Otherwise, the integer literal <code>0</code> would convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, to the key type, causing undefined behavior at runtime.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value of the element to count.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Number of elements with key <code>key</code>. If the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, the return value will be <code>0</code>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>This method always returns <code>0</code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>count</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To check for an array element instead, use <a href=../at/ ><code>at</code></a>, <a href=../operator%5B%5D/ ><code>operator[]</code></a>, or compare against <a href=../size/ ><code>size</code></a>.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) count number of elements</summary> <p>The example shows how <code>count()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <ol> <li>Returns the number of elements with key <code>key</code>. If <code>ObjectType</code> is the default <code>std::map</code> type, the return value will always be <code>0</code> (<code>key</code> was not found) or <code>1</code> (<code>key</code> was found).</li> <li>See 1. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</li> <li>Deleted: this overload is only available if <code>T</code> is an integral type and is declared as deleted, so that a call with an integer <code>key</code> (for example, <code class=highlight><span class=n>j</span><span class=p>.</span><span class=n>count</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) fails to compile. Otherwise, the integer literal <code>0</code> would convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, to the key type, causing undefined behavior at runtime.</li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>key</code> (in)</dt> <dd>key value of the element to count.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>Number of elements with key <code>key</code>. If the <abbr title="JavaScript Object Notation">JSON</abbr> value is not an object, the return value will be <code>0</code>.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Logarithmic in the size of the <abbr title="JavaScript Object Notation">JSON</abbr> object.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>This method always returns <code>0</code> when executed on a <abbr title="JavaScript Object Notation">JSON</abbr> type that is not an object.</li> <li>Calling this function with an integer argument (for example, <code class=highlight><span class=n>count</span><span class=p>(</span><span class=mi>0</span><span class=p>)</span></code>) does not compile: such an argument would otherwise implicitly convert to a null <code class=highlight><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=o>*</span></code> and, from there, cause undefined behavior when constructing a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> for the object key. To check for an array element instead, use <a href=../at/ ><code>at</code></a>, <a href=../operator%5B%5D/ ><code>operator[]</code></a>, or compare against <a href=../size/ ><code>size</code></a>.</li> </ul> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example: (1) count number of elements</summary> <p>The example shows how <code>count()</code> is used.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -33,7 +33,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+2 -2
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@@ -52,7 +52,7 @@ The example shows how `count()` is used.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -86,7 +86,7 @@ The example shows how `count()` is used.
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+1 -1
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@@ -30,7 +30,7 @@ Constant.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
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@@ -1,8 +1,8 @@
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</code></pre></div> <p>Returns an iterator to the reverse-beginning; that is, the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-rbegin-rend.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reverse iterator to the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>crbegin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Returns an iterator to the reverse-beginning; that is, the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-rbegin-rend.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reverse iterator to the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>crbegin()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
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@@ -28,7 +28,7 @@ The following code shows an example for `crbegin()`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+1 -1
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@@ -31,7 +31,7 @@ Constant.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
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@@ -1,8 +1,8 @@
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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/crend/" rel="canonical"><link href=../crbegin/ rel=prev><link href=../default_object_comparator_t/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>crend - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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</code></pre></div> <p>Returns an iterator to the reverse-end; that is, one before the first element. This element acts as a placeholder, attempting to access it results in undefined behavior.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-rbegin-rend.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reverse iterator to the element following the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>crend()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Returns an iterator to the reverse-end; that is, one before the first element. This element acts as a placeholder, attempting to access it results in undefined behavior.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-rbegin-rend.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reverse iterator to the element following the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>crend()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
View File
@@ -28,7 +28,7 @@ The following code shows an example for `crend()`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -24,13 +24,13 @@ The actual comparator used depends on [`object_t`](object_t.md) and can be obtai
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
std::cout << std::boolalpha std::cout << std::boolalpha
<< "one < two : " << json::default_object_comparator_t{}("one", "two") << "\n" << "one < two : " << json::default_object_comparator_t{}("one", "two") << "\n"
<< "three < four : " << json::default_object_comparator_t{}("three", "four") << std::endl; << "three < four : " << json::default_object_comparator_t{}("three", "four") << '\n';
} }
``` ```
@@ -1,16 +1,16 @@
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<span class=k>using</span><span class=w> </span><span class=n>default_object_comparator_t</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>less</span><span class=o>&lt;&gt;</span><span class=p>;</span><span class=w> </span><span class=c1>// since C++14</span> <span class=k>using</span><span class=w> </span><span class=n>default_object_comparator_t</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>less</span><span class=o>&lt;&gt;</span><span class=p>;</span><span class=w> </span><span class=c1>// since C++14</span>
</code></pre></div> <p>The default comparator used by <a href=../object_t/ ><code>object_t</code></a>.</p> <p>Since C++14 a transparent comparator is used which prevents unnecessary string construction when looking up a key in an object.</p> <p>The actual comparator used depends on <a href=../object_t/ ><code>object_t</code></a> and can be obtained via <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below demonstrates the default comparator.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>The default comparator used by <a href=../object_t/ ><code>object_t</code></a>.</p> <p>Since C++14 a transparent comparator is used which prevents unnecessary string construction when looking up a key in an object.</p> <p>The actual comparator used depends on <a href=../object_t/ ><code>object_t</code></a> and can be obtained via <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below demonstrates the default comparator.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>boolalpha</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"one &lt; two : "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>default_object_comparator_t</span><span class=p>{}(</span><span class=s>"one"</span><span class=p>,</span><span class=w> </span><span class=s>"two"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"</span><span class=se>\n</span><span class=s>"</span> <span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"one &lt; two : "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>default_object_comparator_t</span><span class=p>{}(</span><span class=s>"one"</span><span class=p>,</span><span class=w> </span><span class=s>"two"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"</span><span class=se>\n</span><span class=s>"</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"three &lt; four : "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>default_object_comparator_t</span><span class=p>{}(</span><span class=s>"three"</span><span class=p>,</span><span class=w> </span><span class=s>"four"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"three &lt; four : "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>default_object_comparator_t</span><span class=p>{}(</span><span class=s>"three"</span><span class=p>,</span><span class=w> </span><span class=s>"four"</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>o</span><span class=kc>ne</span><span class=w> </span><span class=err>&lt;</span><span class=w> </span><span class=kc>t</span><span class=err>wo</span><span class=w> </span><span class=p>:</span><span class=w> </span><span class=kc>true</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>o</span><span class=kc>ne</span><span class=w> </span><span class=err>&lt;</span><span class=w> </span><span class=kc>t</span><span class=err>wo</span><span class=w> </span><span class=p>:</span><span class=w> </span><span class=kc>true</span>
<span class=kc>t</span><span class=err>hree</span><span class=w> </span><span class=err>&lt;</span><span class=w> </span><span class=kc>f</span><span class=err>our</span><span class=w> </span><span class=p>:</span><span class=w> </span><span class=kc>false</span> <span class=kc>t</span><span class=err>hree</span><span class=w> </span><span class=err>&lt;</span><span class=w> </span><span class=kc>f</span><span class=err>our</span><span class=w> </span><span class=p>:</span><span class=w> </span><span class=kc>false</span>
@@ -22,13 +22,13 @@ The example below demonstrates the default comparator.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
std::cout << std::boolalpha std::cout << std::boolalpha
<< "one < two : " << json::default_object_comparator_t{}("one", "two") << "\n" << "one < two : " << json::default_object_comparator_t{}("one", "two") << "\n"
<< "three < four : " << json::default_object_comparator_t{}("three", "four") << std::endl; << "three < four : " << json::default_object_comparator_t{}("three", "four") << '\n';
} }
``` ```
+43 -6
View File
@@ -2,17 +2,27 @@
```cpp ```cpp
static basic_json diff(const basic_json& source, static basic_json diff(const basic_json& source,
const basic_json& target); const basic_json& target,
const string_t& path = "");
``` ```
Creates a [JSON Patch](http://jsonpatch.com) so that value `source` can be changed into the value `target` by calling Creates a [JSON Patch](http://jsonpatch.com) so that value `source` can be changed into the value `target` by calling
[`patch`](patch.md) function. [`patch`](patch.md) function.
For two JSON values `source` and `target`, the following code always yields `#!cpp true`: For two JSON values `source` and `target`, the following code yields `#!cpp true`:
```cpp ```cpp
source.patch(diff(source, target)) == target; source.patch(diff(source, target)) == target;
``` ```
The equality holds up to [`operator==`](operator_eq.md), so it has the following exceptions:
- A value that is not equal to itself cannot round-trip. This applies to `NaN` (also nested in an array or object) and
to [discarded](is_discarded.md) values: `diff` emits a `replace` operation for them. A `NaN` in the patch is
serialized as `#!json null`, so a patch that was dumped and parsed again would set `#!json null`.
- Numbers that compare equal produce no operation, even if their types or signs differ: `diff(1, 1.0)`,
`diff(1u, 1)` (unsigned and signed integer) and `diff(0.0, -0.0)` all return `#!json []`. The patched value is then
the `source` and keeps its number type.
## Parameters ## Parameters
`source` (in) `source` (in)
@@ -21,6 +31,12 @@ source.patch(diff(source, target)) == target;
`target` (in) `target` (in)
: JSON value to compare against : JSON value to compare against
`path` (in)
: a prefix that is put verbatim in front of the `path` member of every operation (default: `""`, which addresses the
root of the value). The prefix is neither escaped nor validated: `#!cpp diff(1, 2, "abc")` yields an operation with
the `path` `abc`, which is not a valid JSON Pointer. Use it with a valid JSON Pointer such as `/root` and escape
`~` and `/` in its reference tokens (see [JSON Pointer](../../features/json_pointer.md)).
## Return value ## Return value
a JSON patch to convert the `source` to `target` a JSON patch to convert the `source` to `target`
@@ -31,11 +47,32 @@ Strong guarantee: `source` and `target` are never modified.
## Complexity ## Complexity
Linear in the lengths of `source` and `target`. Linear in the total number of values (including nested ones) in `source` and `target`, times the cost of a key-based
object operation (looking up a key in an object): logarithmic for [`json`](../json.md), and linear for
[`ordered_json`](../ordered_json.md) (see [`ordered_map` complexity](../ordered_map.md#complexity)). For
`ordered_json`, diffing two objects with `n` and `m` members therefore takes O((n+m)²) when their keys do not line up
(e.g., a key was added or the keys are in a different order). The size of the patch is proportional to the number of
operations times the length of their paths, so a small change deep inside a value yields a long `path`.
## Notes ## Notes
Currently, only `remove`, `add`, and `replace` operations are generated. - Currently, only `remove`, `add`, and `replace` operations are generated.
- The patch is correct, but not guaranteed to be minimal. For instance, `diff([1,2,3], [0,1,2,3])` yields three
`replace` operations and one `add` operation instead of a single insertion.
- Differences between two arrays are reported index by index. Elements that were added at the end of the array are added
with `add` operations on the path `/-` (appended in order), and elements that were removed are removed with `remove`
operations from the highest index down to the lowest, so that the remaining indices stay valid.
- For objects, the operations for the members of `source` come first (`replace`, `remove`, or the operations for nested
values, in the iteration order of `source`), followed by `add` operations for the members that only `target` has.
- For [`ordered_json`](../ordered_json.md), objects with the same keys in a different order are different. As a patch
cannot reorder members, `diff` removes all keys of the `source` object and adds them again in the order of the
`target`.
- If `source` and `target` differ as a whole (e.g., different types), the patch consists of a single `replace`
operation for the root of the value, i.e., with the `path` `""` (or the given `path` prefix).
- The `value` members of the patch hold copies of values of `target`. A [binary](../../features/binary_values.md) value
has no JSON representation: when a patch that contains one is serialized, it becomes an object such as
`#!json {"bytes":[1,3],"subtype":null}`, so a parsed patch no longer holds a binary value (and would set that object
instead).
## Examples ## Examples
@@ -48,7 +85,7 @@ Currently, only `remove`, `add`, and `replace` operations are generated.
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -79,7 +116,7 @@ Currently, only `remove`, `add`, and `replace` operations are generated.
// output patch and roundtrip result // output patch and roundtrip result
std::cout << std::setw(4) << patch << "\n\n" std::cout << std::setw(4) << patch << "\n\n"
<< std::setw(4) << patched_source << std::endl; << std::setw(4) << patched_source << '\n';
} }
``` ```
+8 -7
View File
@@ -1,11 +1,12 @@
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12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg>Line truncated
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json</span><span class=o>&amp;</span><span class=w> </span><span class=n>target</span><span class=p>);</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json</span><span class=o>&amp;</span><span class=w> </span><span class=n>target</span><span class=p>,</span>
</code></pre></div> <p>Creates a <a href="http://jsonpatch.com"><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a> so that value <code>source</code> can be changed into the value <code>target</code> by calling <a href=../patch/ ><code>patch</code></a> function.</p> <p>For two <abbr title="JavaScript Object Notation">JSON</abbr> values <code>source</code> and <code>target</code>, the following code always yields <code class=highlight><span class=nb>true</span></code>: <div class=highlight><pre><span></span><code><span class=n>source</span><span class=p>.</span><span class=n>patch</span><span class=p>(</span><span class=n>diff</span><span class=p>(</span><span class=n>source</span><span class=p>,</span><span class=w> </span><span class=n>target</span><span class=p>))</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>target</span><span class=p>;</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>string_t</span><span class=o>&amp;</span><span class=w> </span><span class=n>path</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>""</span><span class=p>);</span>
</code></pre></div></p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>source</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to compare from</dd> <dt><code>target</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to compare against</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>a <abbr title="JavaScript Object Notation">JSON</abbr> patch to convert the <code>source</code> to <code>target</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: <code>source</code> and <code>target</code> are never modified.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the lengths of <code>source</code> and <code>target</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Currently, only <code>remove</code>, <code>add</code>, and <code>replace</code> operations are generated.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how a <abbr title="JavaScript Object Notation">JSON</abbr> patch is created as a diff for two <abbr title="JavaScript Object Notation">JSON</abbr> values.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Creates a <a href="http://jsonpatch.com"><abbr title="JavaScript Object Notation">JSON</abbr> Patch</a> so that value <code>source</code> can be changed into the value <code>target</code> by calling <a href=../patch/ ><code>patch</code></a> function.</p> <p>For two <abbr title="JavaScript Object Notation">JSON</abbr> values <code>source</code> and <code>target</code>, the following code yields <code class=highlight><span class=nb>true</span></code>: <div class=highlight><pre><span></span><code><span class=n>source</span><span class=p>.</span><span class=n>patch</span><span class=p>(</span><span class=n>diff</span><span class=p>(</span><span class=n>source</span><span class=p>,</span><span class=w> </span><span class=n>target</span><span class=p>))</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>target</span><span class=p>;</span>
</code></pre></div></p> <p>The equality holds up to <a href=../operator_eq/ ><code>operator==</code></a>, so it has the following exceptions:</p> <ul> <li>A value that is not equal to itself cannot round-trip. This applies to <code>NaN</code> (also nested in an array or object) and to <a href=../is_discarded/ >discarded</a> values: <code>diff</code> emits a <code>replace</code> operation for them. A <code>NaN</code> in the patch is serialized as <code class=highlight><span class=kc>null</span></code>, so a patch that was dumped and parsed again would set <code class=highlight><span class=kc>null</span></code>.</li> <li>Numbers that compare equal produce no operation, even if their types or signs differ: <code>diff(1, 1.0)</code>, <code>diff(1u, 1)</code> (unsigned and signed integer) and <code>diff(0.0, -0.0)</code> all return <code class=highlight><span class=p>[]</span></code>. The patched value is then the <code>source</code> and keeps its number type.</li> </ul> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>source</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to compare from</dd> <dt><code>target</code> (in)</dt> <dd><abbr title="JavaScript Object Notation">JSON</abbr> value to compare against</dd> <dt><code>path</code> (in)</dt> <dd>a prefix that is put verbatim in front of the <code>path</code> member of every operation (default: <code>""</code>, which addresses the root of the value). The prefix is neither escaped nor validated: <code class=highlight><span class=n>diff</span><span class=p>(</span><span class=mi>1</span><span class=p>,</span><span class=w> </span><span class=mi>2</span><span class=p>,</span><span class=w> </span><span class=s>"abc"</span><span class=p>)</span></code> yields an operation with the <code>path</code> <code>abc</code>, which is not a valid <abbr title="JavaScript Object Notation">JSON</abbr> Pointer. Use it with a valid <abbr title="JavaScript Object Notation">JSON</abbr> Pointer such as <code>/root</code> and escape <code>~</code> and <code>/</code> in its reference tokens (see <a href=../../../features/json_pointer/ ><abbr title="JavaScript Object Notation">JSON</abbr> Pointer</a>).</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>a <abbr title="JavaScript Object Notation">JSON</abbr> patch to convert the <code>source</code> to <code>target</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: <code>source</code> and <code>target</code> are never modified.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the total number of values (including nested ones) in <code>source</code> and <code>target</code>, times the cost of a key-based object operation (looking up a key in an object): logarithmic for <a href=../../json/ ><code>json</code></a>, and linear for <a href=../../ordered_json/ ><code>ordered_json</code></a> (see <a href=../../ordered_map/#complexity><code>ordered_map</code> complexity</a>). For <code>ordered_json</code>, diffing two objects with <code>n</code> and <code>m</code> members therefore takes O((n+m)²) when their keys do not line up (e.g., a key was added or the keys are in a different order). The size of the patch is proportional to the number of operations times the length of their paths, so a small change deep inside a value yields a long <code>path</code>.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <ul> <li>Currently, only <code>remove</code>, <code>add</code>, and <code>replace</code> operations are generated.</li> <li>The patch is correct, but not guaranteed to be minimal. For instance, <code>diff([1,2,3], [0,1,2,3])</code> yields three <code>replace</code> operations and one <code>add</code> operation instead of a single insertion.</li> <li>Differences between two arrays are reported index by index. Elements that were added at the end of the array are added with <code>add</code> operations on the path <code>/-</code> (appended in order), and elements that were removed are removed with <code>remove</code> operations from the highest index down to the lowest, so that the remaining indices stay valid.</li> <li>For objects, the operations for the members of <code>source</code> come first (<code>replace</code>, <code>remove</code>, or the operations for nested values, in the iteration order of <code>source</code>), followed by <code>add</code> operations for the members that only <code>target</code> has.</li> <li>For <a href=../../ordered_json/ ><code>ordered_json</code></a>, objects with the same keys in a different order are different. As a patch cannot reorder members, <code>diff</code> removes all keys of the <code>source</code> object and adds them agaLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iomanip&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>nlohmann</span><span class=o>::</span><span class=nn>literals</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
@@ -36,7 +37,7 @@
<span class=w> </span><span class=c1>// output patch and roundtrip result</span> <span class=w> </span><span class=c1>// output patch and roundtrip result</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>4</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>patch</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"</span><span class=se>\n\n</span><span class=s>"</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>4</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>patch</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"</span><span class=se>\n\n</span><span class=s>"</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>4</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>patched_source</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>setw</span><span class=p>(</span><span class=mi>4</span><span class=p>)</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>patched_source</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>[</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=p>[</span>
<span class=w> </span><span class=p>{</span> <span class=w> </span><span class=p>{</span>
@@ -63,4 +64,4 @@
<span class=w> </span><span class=s2>"world"</span> <span class=w> </span><span class=s2>"world"</span>
<span class=w> </span><span class=p>]</span> <span class=w> </span><span class=p>]</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href="https://tools.ietf.org/html/rfc6902"><abbr title="Request for Comments">RFC</abbr> 6902 (<abbr title="JavaScript Object Notation">JSON</abbr> Patch)</a></li> <li><a href=../patch/ >patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch</li> <li><a href=../patch_inplace/ >patch_inplace</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Patch in place</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../merge_diff/ >merge_diff</a> creates a diff as a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 2.0.0.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="October 12, 2026 07:33:43 UTC">October 12, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 2013-2026 Niels Lohmann </div> </div> <div class=md-social> <a href="https://github.com/nlohmann" target="_blank" rel="noopener" title="github.com" class="md-social__link"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 512 512"><!-- Font Awesome Free 7.1.0 by @fontawesome - 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+20 -6
View File
@@ -2,23 +2,31 @@
``` ```
static basic_json diff(const basic_json& source, static basic_json diff(const basic_json& source,
const basic_json& target); const basic_json& target,
const string_t& path = "");
``` ```
Creates a [JSON Patch](http://jsonpatch.com) so that value `source` can be changed into the value `target` by calling [`patch`](https://json.nlohmann.me/api/basic_json/patch/index.md) function. Creates a [JSON Patch](http://jsonpatch.com) so that value `source` can be changed into the value `target` by calling [`patch`](https://json.nlohmann.me/api/basic_json/patch/index.md) function.
For two JSON values `source` and `target`, the following code always yields `true`: For two JSON values `source` and `target`, the following code yields `true`:
``` ```
source.patch(diff(source, target)) == target; source.patch(diff(source, target)) == target;
``` ```
The equality holds up to [`operator==`](https://json.nlohmann.me/api/basic_json/operator_eq/index.md), so it has the following exceptions:
- A value that is not equal to itself cannot round-trip. This applies to `NaN` (also nested in an array or object) and to [discarded](https://json.nlohmann.me/api/basic_json/is_discarded/index.md) values: `diff` emits a `replace` operation for them. A `NaN` in the patch is serialized as `null`, so a patch that was dumped and parsed again would set `null`.
- Numbers that compare equal produce no operation, even if their types or signs differ: `diff(1, 1.0)`, `diff(1u, 1)` (unsigned and signed integer) and `diff(0.0, -0.0)` all return `[]`. The patched value is then the `source` and keeps its number type.
## Parameters ## Parameters
`source` (in) : JSON value to compare from `source` (in) : JSON value to compare from
`target` (in) : JSON value to compare against `target` (in) : JSON value to compare against
`path` (in) : a prefix that is put verbatim in front of the `path` member of every operation (default: `""`, which addresses the root of the value). The prefix is neither escaped nor validated: `diff(1, 2, "abc")` yields an operation with the `path` `abc`, which is not a valid JSON Pointer. Use it with a valid JSON Pointer such as `/root` and escape `~` and `/` in its reference tokens (see [JSON Pointer](https://json.nlohmann.me/features/json_pointer/index.md)).
## Return value ## Return value
a JSON patch to convert the `source` to `target` a JSON patch to convert the `source` to `target`
@@ -29,11 +37,17 @@ Strong guarantee: `source` and `target` are never modified.
## Complexity ## Complexity
Linear in the lengths of `source` and `target`. Linear in the total number of values (including nested ones) in `source` and `target`, times the cost of a key-based object operation (looking up a key in an object): logarithmic for [`json`](https://json.nlohmann.me/api/json/index.md), and linear for [`ordered_json`](https://json.nlohmann.me/api/ordered_json/index.md) (see [`ordered_map` complexity](https://json.nlohmann.me/api/ordered_map/#complexity)). For `ordered_json`, diffing two objects with `n` and `m` members therefore takes O((n+m)²) when their keys do not line up (e.g., a key was added or the keys are in a different order). The size of the patch is proportional to the number of operations times the length of their paths, so a small change deep inside a value yields a long `path`.
## Notes ## Notes
Currently, only `remove`, `add`, and `replace` operations are generated. - Currently, only `remove`, `add`, and `replace` operations are generated.
- The patch is correct, but not guaranteed to be minimal. For instance, `diff([1,2,3], [0,1,2,3])` yields three `replace` operations and one `add` operation instead of a single insertion.
- Differences between two arrays are reported index by index. Elements that were added at the end of the array are added with `add` operations on the path `/-` (appended in order), and elements that were removed are removed with `remove` operations from the highest index down to the lowest, so that the remaining indices stay valid.
- For objects, the operations for the members of `source` come first (`replace`, `remove`, or the operations for nested values, in the iteration order of `source`), followed by `add` operations for the members that only `target` has.
- For [`ordered_json`](https://json.nlohmann.me/api/ordered_json/index.md), objects with the same keys in a different order are different. As a patch cannot reorder members, `diff` removes all keys of the `source` object and adds them again in the order of the `target`.
- If `source` and `target` differ as a whole (e.g., different types), the patch consists of a single `replace` operation for the root of the value, i.e., with the `path` `""` (or the given `path` prefix).
- The `value` members of the patch hold copies of values of `target`. A [binary](https://json.nlohmann.me/features/binary_values/index.md) value has no JSON representation: when a patch that contains one is serialized, it becomes an object such as `{"bytes":[1,3],"subtype":null}`, so a parsed patch no longer holds a binary value (and would set that object instead).
## Examples ## Examples
@@ -46,7 +60,7 @@ The following code shows how a JSON patch is created as a diff for two JSON valu
#include <iomanip> #include <iomanip>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
using namespace nlohmann::literals; using namespace nlohmann::literals;
int main() int main()
@@ -77,7 +91,7 @@ int main()
// output patch and roundtrip result // output patch and roundtrip result
std::cout << std::setw(4) << patch << "\n\n" std::cout << std::setw(4) << patch << "\n\n"
<< std::setw(4) << patched_source << std::endl; << std::setw(4) << patched_source << '\n';
} }
``` ```
+3 -3
View File
@@ -81,7 +81,7 @@ Binary values are serialized as an object containing two keys:
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -113,11 +113,11 @@ Binary values are serialized as an object containing two keys:
json j_invalid = "ä\xA9ü"; json j_invalid = "ä\xA9ü";
try try
{ {
std::cout << j_invalid.dump() << std::endl; std::cout << j_invalid.dump() << '\n';
} }
catch (const json::type_error& e) catch (const json::type_error& e)
{ {
std::cout << e.what() << std::endl; std::cout << e.what() << '\n';
} }
std::cout << "string with replaced invalid characters: " std::cout << "string with replaced invalid characters: "
+4 -4
View File
@@ -1,11 +1,11 @@
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12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <div classLine truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/dump/" rel="canonical"><link href=../diff/ rel=prev><link href=../emplace/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>dump - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link 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<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=w> </span><span class=n>indent_char</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sc>' '</span><span class=p>,</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=w> </span><span class=n>indent_char</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sc>' '</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ensure_ascii</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ensure_ascii</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>error_handler_t</span><span class=w> </span><span class=n>error_handler</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>error_handler_t</span><span class=o>::</span><span class=n>strict</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span> <span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>error_handler_t</span><span class=w> </span><span class=n>error_handler</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>error_handler_t</span><span class=o>::</span><span class=n>strict</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
</code></pre></div> <p>Serialization function for <abbr title="JavaScript Object Notation">JSON</abbr> values. The function tries to mimic Python's <a href="https://docs.python.org/2/library/json.html#json.dump"><code>json.dumps()</code> function</a>, and currently supports its <code>indent</code> and <code>ensure_ascii</code> parameters.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>indent</code> (in)</dt> <dd>If <code>indent</code> is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of <code>0</code> will only insert newlines. <code>-1</code> (the default) selects the most compact representation.</dd> <dt><code>indent_char</code> (in)</dt> <dd>The character to use for indentation if <code>indent</code> is greater than <code>0</code>. The default is <code></code> (space).</dd> <dt><code>ensure_ascii</code> (in)</dt> <dd>If <code>ensure_ascii</code> is true, all non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters in the output are escaped with <code>\uXXXX</code> sequences, and the result consists of <abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters only.</dd> <dt><code>error_handler</code> (in)</dt> <dd>how to react on decoding errors; there are four possible values (see <a href=../error_handler_t/ ><code>error_handler_t</code></a>: <code>strict</code> (throws an exception in case a decoding error occurs; default), <code>replace</code> (replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD), <code>ignore</code> (ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences during serialization; all valid bytes are copied to the output unchanged, and invalid bytes are dropped), and <code>keep</code> (write the ill-formed bytes to the output as is, without escaping them, even if <code>ensure_ascii</code> is <code class=highlight><span class=nb>true</span></code>; the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, but equals the input bytes exactly, and well-formed characters around the ill-formed bytes are still escaped as usual)).</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>string containing the serialization of the <abbr title="JavaScript Object Notation">JSON</abbr> value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> if a string stored inside the <abbr title="JavaScript Object Notation">JSON</abbr> value is not <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoded and <code>error_handler</code> is set to <code>strict</code></p> <div class="admonition warning"> <p class=admonition-title>Serializing untrusted input</p> <p>When serializing values that may contain invalid or untrusted <abbr title="Unicode Transformation Format">UTF</abbr>-8 (e.g., bytes taken directly from network input), <code>dump()</code> throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> in the default <code>strict</code> mode. To serialize such data without throwing, pass <a href=../error_handler_t/ ><code>error_handler_t::replace</code></a> (substitutes U+FFFD) or <a href=../error_handler_t/ ><code>error_handler_t::ignore</code></a>. Callers that serialize untrusted input on a crash-sensitive path should either choose a non-strict error handler or wrap <code>dump()</code> in a <code class=highlight><span class=k>try</span></code>/<code class=highlight><span class=k>catch</span></code>.</p> <p>See the <a href=../../../home/faq/#serializing-untrusted-or-invalid-utf-8><abbr title="Frequently Asked Questions">FAQ</abbr></a> for details.</p> </div> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Floating-point numbers are written with the fewest digits that read back as the same value (for <code class=highlight><span class=kt>double</span></code>; see <a href=../../../features/types/number_handling/#number-serialization>number handling</a>).</p> <p>Binary values are serialized as an object containing two keys:</p> <ul> <li>"bytes": an array of bytes as integers</li> <li>"subtype": the subtype as integer or <code class=highlight><span class=kc>null</span></code> if the binary has no subtype</li> </ul> <h2 id=exaLine truncated </code></pre></div> <p>Serialization function for <abbr title="JavaScript Object Notation">JSON</abbr> values. The function tries to mimic Python's <a href="https://docs.python.org/2/library/json.html#json.dump"><code>json.dumps()</code> function</a>, and currently supports its <code>indent</code> and <code>ensure_ascii</code> parameters.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>indent</code> (in)</dt> <dd>If <code>indent</code> is nonnegative, then array elements and object members will be pretty-printed with that indent level. An indent level of <code>0</code> will only insert newlines. <code>-1</code> (the default) selects the most compact representation.</dd> <dt><code>indent_char</code> (in)</dt> <dd>The character to use for indentation if <code>indent</code> is greater than <code>0</code>. The default is <code></code> (space).</dd> <dt><code>ensure_ascii</code> (in)</dt> <dd>If <code>ensure_ascii</code> is true, all non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters in the output are escaped with <code>\uXXXX</code> sequences, and the result consists of <abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters only.</dd> <dt><code>error_handler</code> (in)</dt> <dd>how to react on decoding errors; there are four possible values (see <a href=../error_handler_t/ ><code>error_handler_t</code></a>: <code>strict</code> (throws an exception in case a decoding error occurs; default), <code>replace</code> (replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD), <code>ignore</code> (ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences during serialization; all valid bytes are copied to the output unchanged, and invalid bytes are dropped), and <code>keep</code> (write the ill-formed bytes to the output as is, without escaping them, even if <code>ensure_ascii</code> is <code class=highlight><span class=nb>true</span></code>; the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, but equals the input bytes exactly, and well-formed characters around the ill-formed bytes are still escaped as usual)).</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>string containing the serialization of the <abbr title="JavaScript Object Notation">JSON</abbr> value</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> if a string stored inside the <abbr title="JavaScript Object Notation">JSON</abbr> value is not <abbr title="Unicode Transformation Format">UTF</abbr>-8 encoded and <code>error_handler</code> is set to <code>strict</code></p> <div class="admonition warning"> <p class=admonition-title>Serializing untrusted input</p> <p>When serializing values that may contain invalid or untrusted <abbr title="Unicode Transformation Format">UTF</abbr>-8 (e.g., bytes taken directly from network input), <code>dump()</code> throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> in the default <code>strict</code> mode. To serialize such data without throwing, pass <a href=../error_handler_t/ ><code>error_handler_t::replace</code></a> (substitutes U+FFFD) or <a href=../error_handler_t/ ><code>error_handler_t::ignore</code></a>. Callers that serialize untrusted input on a crash-sensitive path should either choose a non-strict error handler or wrap <code>dump()</code> in a <code class=highlight><span class=k>try</span></code>/<code class=highlight><span class=k>catch</span></code>.</p> <p>See the <a href=../../../home/faq/#serializing-untrusted-or-invalid-utf-8><abbr title="Frequently Asked Questions">FAQ</abbr></a> for details.</p> </div> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Floating-point numbers are written with the fewest digits that read back as the same value (for <code class=highlight><span class=kt>double</span></code>; see <a href=../../../features/types/number_handling/#number-serialization>number handling</a>).</p> <p>Binary values are serialized as an object containing two keys:</p> <ul> <li>"bytes": an array of bytes as integers</li> <li>"subtype": the subtype as integer or <code class=highlight><span class=kc>null</span></code> if the binary has no subtype</li> </ul> <h2 id=exaLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -37,11 +37,11 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_invalid</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"ä</span><span class=se>\xA9</span><span class=s>ü"</span><span class=p>;</span> <span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_invalid</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"ä</span><span class=se>\xA9</span><span class=s>ü"</span><span class=p>;</span>
<span class=w> </span><span class=k>try</span> <span class=w> </span><span class=k>try</span>
<span class=w> </span><span class=p>{</span> <span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_invalid</span><span class=p>.</span><span class=n>dump</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_invalid</span><span class=p>.</span><span class=n>dump</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span> <span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>type_error</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span> <span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>type_error</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span> <span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span> <span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"string with replaced invalid characters: "</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"string with replaced invalid characters: "</span>
+3 -3
View File
@@ -60,7 +60,7 @@ The following example shows the effect of different `indent`, `indent_char`, and
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -92,11 +92,11 @@ int main()
json j_invalid = "ä\xA9ü"; json j_invalid = "ä\xA9ü";
try try
{ {
std::cout << j_invalid.dump() << std::endl; std::cout << j_invalid.dump() << '\n';
} }
catch (const json::type_error& e) catch (const json::type_error& e)
{ {
std::cout << e.what() << std::endl; std::cout << e.what() << '\n';
} }
std::cout << "string with replaced invalid characters: " std::cout << "string with replaced invalid characters: "
+1 -1
View File
@@ -55,7 +55,7 @@ Logarithmic in the size of the container, O(log(`size()`)).
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
View File
@@ -1,9 +1,9 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/emplace/" rel="canonical"><link href=../dump/ rel=prev><link href=../emplace_back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>emplace - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/emplace/" rel="canonical"><link href=../dump/ rel=prev><link href=../emplace_back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>emplace - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonemplace class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> emplace </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=n>std</span><span class=o>::</span><span class=n>pair</span><span class=o>&lt;</span><span class=n>iterator</span><span class=p>,</span><span class=w> </span><span class=kt>bool</span><span class=o>&gt;</span><span class=w> </span><span class=n>emplace</span><span class=p>(</span><span class=n>Args</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=p>...</span><span class=w> </span><span class=n>args</span><span class=p>);</span> <span class=n>std</span><span class=o>::</span><span class=n>pair</span><span class=o>&lt;</span><span class=n>iterator</span><span class=p>,</span><span class=w> </span><span class=kt>bool</span><span class=o>&gt;</span><span class=w> </span><span class=n>emplace</span><span class=p>(</span><span class=n>Args</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=p>...</span><span class=w> </span><span class=n>args</span><span class=p>);</span>
</code></pre></div> <p>Inserts a new element into a <abbr title="JavaScript Object Notation">JSON</abbr> object constructed in-place with the given <code>args</code> if there is no element with the key in the container. If the function is called on a <abbr title="JavaScript Object Notation">JSON</abbr> null value, an empty object is created before appending the value created from <code>args</code>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>Args</code></dt> <dd>compatible types to create a <code>basic_json</code> object</dd> </dl> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">&para;</a></h2> <p>For <a href=../../ordered_json/ ><code>ordered_json</code></a>, adding a value to an object can yield a reallocation, in which case all iterators (including the <code>end()</code> iterator) and all references to the elements are invalidated.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>args</code> (in)</dt> <dd>arguments to forward to a constructor of <code>basic_json</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a <code class=highlight><span class=kt>bool</span></code> denoting whether the insertion took place.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value. As an exception, a <code class=highlight><span class=kc>null</span></code> value is converted to an empty object before the element is added and keeps that type if adding the element throws.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error311><code>type_error.311</code></a> when called on a type other than <abbr title="JavaScript Object Notation">JSON</abbr> object or <code class=highlight><span class=kc>null</span></code>; example: <code>"cannot use emplace() with number"</code></p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Logarithmic in the size of the container, O(log(<code>size()</code>)).</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how <code>emplace()</code> can be used to add elements to a <abbr title="JavaScript Object Notation">JSON</abbr> object. Note how the <code class=highlight><span class=kc>null</span></code> value was silently converted to a <abbr title="JavaScript Object Notation">JSON</abbr> object. Further note how no value is added if there was already one value stored with the same key.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Inserts a new element into a <abbr title="JavaScript Object Notation">JSON</abbr> object constructed in-place with the given <code>args</code> if there is no element with the key in the container. If the function is called on a <abbr title="JavaScript Object Notation">JSON</abbr> null value, an empty object is created before appending the value created from <code>args</code>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>Args</code></dt> <dd>compatible types to create a <code>basic_json</code> object</dd> </dl> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">&para;</a></h2> <p>For <a href=../../ordered_json/ ><code>ordered_json</code></a>, adding a value to an object can yield a reallocation, in which case all iterators (including the <code>end()</code> iterator) and all references to the elements are invalidated.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>args</code> (in)</dt> <dd>arguments to forward to a constructor of <code>basic_json</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a <code class=highlight><span class=kt>bool</span></code> denoting whether the insertion took place.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value. As an exception, a <code class=highlight><span class=kc>null</span></code> value is converted to an empty object before the element is added and keeps that type if adding the element throws.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error311><code>type_error.311</code></a> when called on a type other than <abbr title="JavaScript Object Notation">JSON</abbr> object or <code class=highlight><span class=kc>null</span></code>; example: <code>"cannot use emplace() with number"</code></p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Logarithmic in the size of the container, O(log(<code>size()</code>)).</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how <code>emplace()</code> can be used to add elements to a <abbr title="JavaScript Object Notation">JSON</abbr> object. Note how the <code class=highlight><span class=kc>null</span></code> value was silently converted to a <abbr title="JavaScript Object Notation">JSON</abbr> object. Further note how no value is added if there was already one value stored with the same key.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
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@@ -45,7 +45,7 @@ The example shows how `emplace()` can be used to add elements to a JSON object.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+1 -1
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@@ -53,7 +53,7 @@ Amortized constant.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
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@@ -1,9 +1,9 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/emplace_back/" rel="canonical"><link href=../emplace/ rel=prev><link href=../empty/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>emplace_back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> emplace_back </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/emplace_back/" rel="canonical"><link href=../emplace/ rel=prev><link href=../empty/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>emplace_back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_jsonemplace_back class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> emplace_back </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo 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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 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<span class=n>reference</span><span class=w> </span><span class=n>emplace_back</span><span class=p>(</span><span class=n>Args</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=p>...</span><span class=w> </span><span class=n>args</span><span class=p>);</span> <span class=n>reference</span><span class=w> </span><span class=n>emplace_back</span><span class=p>(</span><span class=n>Args</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=p>...</span><span class=w> </span><span class=n>args</span><span class=p>);</span>
</code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> value from the passed parameters <code>args</code> to the end of the <abbr title="JavaScript Object Notation">JSON</abbr> value. If the function is called on a <abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=kc>null</span></code> value, an empty array is created before appending the value created from <code>args</code>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>Args</code></dt> <dd>compatible types to create a <code>basic_json</code> object</dd> </dl> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">&para;</a></h2> <p>By adding an element to the end of the array, a reallocation can happen, in which case all iterators (including the <a href=../end/ ><code>end()</code></a> iterator) and all references to the elements are invalidated. Otherwise, only the <a href=../end/ ><code>end()</code></a> iterator is invalidated.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>args</code> (in)</dt> <dd>arguments to forward to a constructor of <code>basic_json</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reference to the inserted element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value. As an exception, a <code class=highlight><span class=kc>null</span></code> value is converted to an empty array before the element is added and keeps that type if adding the element throws.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error311><code>type_error.311</code></a> when called on a type other than <abbr title="JavaScript Object Notation">JSON</abbr> array or <code class=highlight><span class=kc>null</span></code>; example: <code>"cannot use emplace_back() with number"</code></p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Amortized constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how <code>emplace_back()</code> can be used to add elements to a <abbr title="JavaScript Object Notation">JSON</abbr> array. Note how the <code>null</code> value was silently converted to a <abbr title="JavaScript Object Notation">JSON</abbr> array.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Creates a <abbr title="JavaScript Object Notation">JSON</abbr> value from the passed parameters <code>args</code> to the end of the <abbr title="JavaScript Object Notation">JSON</abbr> value. If the function is called on a <abbr title="JavaScript Object Notation">JSON</abbr> <code class=highlight><span class=kc>null</span></code> value, an empty array is created before appending the value created from <code>args</code>.</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>Args</code></dt> <dd>compatible types to create a <code>basic_json</code> object</dd> </dl> <h2 id=iterator-invalidation>Iterator invalidation<a class=headerlink href=#iterator-invalidation title="Permanent link">&para;</a></h2> <p>By adding an element to the end of the array, a reallocation can happen, in which case all iterators (including the <a href=../end/ ><code>end()</code></a> iterator) and all references to the elements are invalidated. Otherwise, only the <a href=../end/ ><code>end()</code></a> iterator is invalidated.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>args</code> (in)</dt> <dd>arguments to forward to a constructor of <code>basic_json</code></dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>reference to the inserted element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: if an exception is thrown, there are no changes to any <abbr title="JavaScript Object Notation">JSON</abbr> value. As an exception, a <code class=highlight><span class=kc>null</span></code> value is converted to an empty array before the element is added and keeps that type if adding the element throws.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error311><code>type_error.311</code></a> when called on a type other than <abbr title="JavaScript Object Notation">JSON</abbr> array or <code class=highlight><span class=kc>null</span></code>; example: <code>"cannot use emplace_back() with number"</code></p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Amortized constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example shows how <code>emplace_back()</code> can be used to add elements to a <abbr title="JavaScript Object Notation">JSON</abbr> array. Note how the <code>null</code> value was silently converted to a <abbr title="JavaScript Object Notation">JSON</abbr> array.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
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@@ -45,7 +45,7 @@ The example shows how `emplace_back()` can be used to add elements to a JSON arr
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+1 -1
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@@ -54,7 +54,7 @@ itself is empty which is `#!cpp false` in the case of a string.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
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@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/empty/" rel="canonical"><link href=../emplace_back/ rel=prev><link href=../end/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>empty - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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</code></pre></div> <p>Checks if a <abbr title="JavaScript Object Notation">JSON</abbr> value has no elements (i.e., whether its <a href=../size/ ><code>size()</code></a> is <code>0</code>).</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The return value depends on the different types and is defined as follows:</p> <table> <thead> <tr> <th>Value type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td>boolean</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>string</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>number</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>binary</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>object</td> <td>result of function <code>object_t::empty()</code></td> </tr> <tr> <td>array</td> <td>result of function <code>array_t::empty()</code></td> </tr> </tbody> </table> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant, as long as <a href=../array_t/ ><code>array_t</code></a> and <a href=../object_t/ ><code>object_t</code></a> satisfy the <a href="https://en.cppreference.com/w/cpp/named_req/Container">Container</a> concept; that is, their <code>empty()</code> functions have constant complexity.</p> <h2 id=possible-implementation>Possible implementation<a class=headerlink href=#possible-implementation title="Permanent link">&para;</a></h2> <div class=highlight><pre><span></span><code><span class=kt>bool</span><span class=w> </span><span class=nf>empty</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span> </code></pre></div> <p>Checks if a <abbr title="JavaScript Object Notation">JSON</abbr> value has no elements (i.e., whether its <a href=../size/ ><code>size()</code></a> is <code>0</code>).</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The return value depends on the different types and is defined as follows:</p> <table> <thead> <tr> <th>Value type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td>null</td> <td><code class=highlight><span class=nb>true</span></code></td> </tr> <tr> <td>boolean</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>string</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>number</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>binary</td> <td><code class=highlight><span class=nb>false</span></code></td> </tr> <tr> <td>object</td> <td>result of function <code>object_t::empty()</code></td> </tr> <tr> <td>array</td> <td>result of function <code>array_t::empty()</code></td> </tr> </tbody> </table> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant, as long as <a href=../array_t/ ><code>array_t</code></a> and <a href=../object_t/ ><code>object_t</code></a> satisfy the <a href="https://en.cppreference.com/w/cpp/named_req/Container">Container</a> concept; that is, their <code>empty()</code> functions have constant complexity.</p> <h2 id=possible-implementation>Possible implementation<a class=headerlink href=#possible-implementation title="Permanent link">&para;</a></h2> <div class=highlight><pre><span></span><code><span class=kt>bool</span><span class=w> </span><span class=nf>empty</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span>
<span class=p>{</span> <span class=p>{</span>
<span class=w> </span><span class=k>return</span><span class=w> </span><span class=n>size</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=mi>0</span><span class=p>;</span> <span class=w> </span><span class=k>return</span><span class=w> </span><span class=n>size</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=mi>0</span><span class=p>;</span>
@@ -6,7 +6,7 @@
</code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This function does not return whether a string stored as <abbr title="JavaScript Object Notation">JSON</abbr> value is empty -- it returns whether the <abbr title="JavaScript Object Notation">JSON</abbr> container itself is empty which is <code class=highlight><span class=nb>false</span></code> in the case of a string.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code uses <code>empty()</code> to check if a <abbr title="JavaScript Object Notation">JSON</abbr> object contains any elements.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>This function does not return whether a string stored as <abbr title="JavaScript Object Notation">JSON</abbr> value is empty -- it returns whether the <abbr title="JavaScript Object Notation">JSON</abbr> container itself is empty which is <code class=highlight><span class=nb>false</span></code> in the case of a string.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code uses <code>empty()</code> to check if a <abbr title="JavaScript Object Notation">JSON</abbr> object contains any elements.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
View File
@@ -51,7 +51,7 @@ The following code uses `empty()` to check if a JSON object contains any element
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+1 -1
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@@ -31,7 +31,7 @@ Constant.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+2 -2
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@@ -1,9 +1,9 @@
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<span class=n>const_iterator</span><span class=w> </span><span class=nf>end</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span> <span class=n>const_iterator</span><span class=w> </span><span class=nf>end</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
</code></pre></div> <p>Returns an iterator to one past the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>end()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Returns an iterator to one past the last element.</p> <p><img alt="Illustration from cppreference.com" src=../../../images/range-begin-end.svg></p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>iterator one past the last element</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows an example for <code>end()</code>.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
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@@ -29,7 +29,7 @@ The following code shows an example for `end()`.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+1 -1
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@@ -52,7 +52,7 @@ Constant.
#define JSON_DIAGNOSTIC_POSITIONS 1 #define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
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@@ -1,4 +1,4 @@
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<span class=k>constexpr</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=w> </span><span class=nf>end_pos</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span> <span class=k>constexpr</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=w> </span><span class=nf>end_pos</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
<span class=cp>#endif</span> <span class=cp>#endif</span>
</code></pre></div> <p>Returns the position immediately following the last character of the <abbr title="JavaScript Object Notation">JSON</abbr> string from which the value was parsed from.</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td>object</td> <td>position after the closing <code>}</code></td> </tr> <tr> <td>array</td> <td>position after the closing <code>]</code></td> </tr> <tr> <td>string</td> <td>position after the closing <code>"</code></td> </tr> <tr> <td>number</td> <td>position after the last character</td> </tr> <tr> <td>boolean</td> <td>position after <code>e</code></td> </tr> <tr> <td>null</td> <td>position after <code>l</code></td> </tr> </tbody> </table> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>the position of the character <em>following</em> the last character of the given value in the parsed <abbr title="JavaScript Object Notation">JSON</abbr> string, if the value was created by the <a href=../parse/ ><code>parse</code></a> function, or <code>std::string::npos</code> if the value was constructed otherwise</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Note</p> <p>The function is only available if macro <a href=../../macros/json_diagnostic_positions/ ><code>JSON_DIAGNOSTIC_POSITIONS</code></a> has been defined to <code class=highlight><span class=mi>1</span></code> before including the library header.</p> </div> <div class="admonition warning"> <p class=admonition-title>Invalidation</p> <p>The returned positions are only valid as long as the <abbr title="JavaScript Object Notation">JSON</abbr> value is not changed. The positions are <em>not</em> updated when the <abbr title="JavaScript Object Notation">JSON</abbr> value is changed.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>Returns the position immediately following the last character of the <abbr title="JavaScript Object Notation">JSON</abbr> string from which the value was parsed from.</p> <table> <thead> <tr> <th><abbr title="JavaScript Object Notation">JSON</abbr> type</th> <th>return value</th> </tr> </thead> <tbody> <tr> <td>object</td> <td>position after the closing <code>}</code></td> </tr> <tr> <td>array</td> <td>position after the closing <code>]</code></td> </tr> <tr> <td>string</td> <td>position after the closing <code>"</code></td> </tr> <tr> <td>number</td> <td>position after the last character</td> </tr> <tr> <td>boolean</td> <td>position after <code>e</code></td> </tr> <tr> <td>null</td> <td>position after <code>l</code></td> </tr> </tbody> </table> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>the position of the character <em>following</em> the last character of the given value in the parsed <abbr title="JavaScript Object Notation">JSON</abbr> string, if the value was created by the <a href=../parse/ ><code>parse</code></a> function, or <code>std::string::npos</code> if the value was constructed otherwise</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>No-throw guarantee: this member function never throws exceptions.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Constant.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <div class="admonition note"> <p class=admonition-title>Note</p> <p>The function is only available if macro <a href=../../macros/json_diagnostic_positions/ ><code>JSON_DIAGNOSTIC_POSITIONS</code></a> has been defined to <code class=highlight><span class=mi>1</span></code> before including the library header.</p> </div> <div class="admonition warning"> <p class=admonition-title>Invalidation</p> <p>The returned positions are only valid as long as the <abbr title="JavaScript Object Notation">JSON</abbr> value is not changed. The positions are <em>not</em> updated when the <abbr title="JavaScript Object Notation">JSON</abbr> value is changed.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
@@ -6,7 +6,7 @@
<span class=cp>#define JSON_DIAGNOSTIC_POSITIONS 1</span> <span class=cp>#define JSON_DIAGNOSTIC_POSITIONS 1</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+1 -1
View File
@@ -49,7 +49,7 @@ Example
#define JSON_DIAGNOSTIC_POSITIONS 1 #define JSON_DIAGNOSTIC_POSITIONS 1
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+5 -5
View File
@@ -140,7 +140,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -191,7 +191,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -242,7 +242,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -278,7 +278,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -312,7 +312,7 @@ Strong exception safety: if an exception occurs, the original value stays intact
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+6 -6
View File
@@ -1,4 +1,4 @@
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1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </laLine truncated
<span class=n>iterator</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>iterator</span><span class=w> </span><span class=n>pos</span><span class=p>);</span> <span class=n>iterator</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>iterator</span><span class=w> </span><span class=n>pos</span><span class=p>);</span>
<span class=n>const_iterator</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>const_iterator</span><span class=w> </span><span class=n>pos</span><span class=p>);</span> <span class=n>const_iterator</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>const_iterator</span><span class=w> </span><span class=n>pos</span><span class=p>);</span>
@@ -18,7 +18,7 @@
</code></pre></div> <ol> <li> <p>Removes an element from a <abbr title="JavaScript Object Notation">JSON</abbr> value specified by iterator <code>pos</code>. The iterator <code>pos</code> must be valid and dereferenceable. Thus, the <code>end()</code> iterator (which is valid, but is not dereferenceable) cannot be used as a value for <code>pos</code>.</p> <p>If called on a primitive type other than <code class=highlight><span class=kc>null</span></code>, the resulting <abbr title="JavaScript Object Notation">JSON</abbr> value will be <code class=highlight><span class=kc>null</span></code>.</p> </li> <li> <p>Remove an element range specified by <code>[first; last)</code> from a <abbr title="JavaScript Object Notation">JSON</abbr> value. The iterator <code>first</code> does not need to be dereferenceable if <code>first == last</code>: erasing an empty range is a no-op.</p> <p>If called on a primitive type other than <code class=highlight><span class=kc>null</span></code>, the resulting <abbr title="JavaScript Object Notation">JSON</abbr> value will be <code class=highlight><span class=kc>null</span></code>.</p> </li> <li> <p>Removes an element from a <abbr title="JavaScript Object Notation">JSON</abbr> object by key.</p> </li> <li> <p>See 3. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</p> </li> <li> <p>Removes an element from a <abbr title="JavaScript Object Notation">JSON</abbr> array by index.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>pos</code> (in)</dt> <dd>iterator to the element to remove</dd> <dt><code>first</code> (in)</dt> <dd>iterator to the beginning of the range to remove</dd> <dt><code>last</code> (in)</dt> <dd>iterator past the end of the range to remove</dd> <dt><code>key</code> (in)</dt> <dd>object key of the elements to remove</dd> <dt><code>idx</code> (in)</dt> <dd>array index of the element to remove</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li>Iterator following the last removed element. If the iterator <code>pos</code> refers to the last element, the <code>end()</code> iterator is returned.</li> <li>Iterator following the last removed element. If the iterator <code>last</code> refers to the last element, the <code>end()</code> iterator is returned.</li> <li>Number of elements removed. If <code>ObjectType</code> is the default <code>std::map</code> type, the return value will always be <code>0</code> (<code>key</code> was not found) or <code>1</code> (<code>key</code> was found).</li> <li>See 3.</li> <li>(none)</li> </ol> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <ol> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error307><code>type_error.307</code></a> if called on a <code>null</code> value; example: <code>"cannot use erase() with null"</code></li> <li>Throws <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator202><code>invalid_iterator.202</code></a> if called on an iterator which does not belong to the current <abbr title="JavaScript Object Notation">JSON</abbr> value; example: <code>"iterator does not fit current value"</code></li> <li>Throws <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator205><code>invalid_iterator.205</code></a> if called on a primitive type with invalid iterator (i.e., any iterator which is not <code>begin()</code>); example: <code>"iterator out of range"</code></li> </ul> </li> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error307><code>type_error.307</code></a> if called on a <code>null</code> value; example: <code>"cannot use erase() with null"</code></li> <li>Throws <a href=../../../home/exceptions/#jsoneLine truncated </code></pre></div> <ol> <li> <p>Removes an element from a <abbr title="JavaScript Object Notation">JSON</abbr> value specified by iterator <code>pos</code>. The iterator <code>pos</code> must be valid and dereferenceable. Thus, the <code>end()</code> iterator (which is valid, but is not dereferenceable) cannot be used as a value for <code>pos</code>.</p> <p>If called on a primitive type other than <code class=highlight><span class=kc>null</span></code>, the resulting <abbr title="JavaScript Object Notation">JSON</abbr> value will be <code class=highlight><span class=kc>null</span></code>.</p> </li> <li> <p>Remove an element range specified by <code>[first; last)</code> from a <abbr title="JavaScript Object Notation">JSON</abbr> value. The iterator <code>first</code> does not need to be dereferenceable if <code>first == last</code>: erasing an empty range is a no-op.</p> <p>If called on a primitive type other than <code class=highlight><span class=kc>null</span></code>, the resulting <abbr title="JavaScript Object Notation">JSON</abbr> value will be <code class=highlight><span class=kc>null</span></code>.</p> </li> <li> <p>Removes an element from a <abbr title="JavaScript Object Notation">JSON</abbr> object by key.</p> </li> <li> <p>See 3. This overload is only available if <code>KeyType</code> is comparable with <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_t</span><span class=o>::</span><span class=n>key_type</span></code> and <code class=highlight><span class=k>typename</span><span class=w> </span><span class=nc>object_comparator_t</span><span class=o>::</span><span class=n>is_transparent</span></code> denotes a type.</p> </li> <li> <p>Removes an element from a <abbr title="JavaScript Object Notation">JSON</abbr> array by index.</p> </li> </ol> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>KeyType</code></dt> <dd>A type for an object key other than <a href=../../json_pointer/ ><code>json_pointer</code></a> that is comparable with <a href=../string_t/ ><code>string_t</code></a> using <a href=../object_comparator_t/ ><code>object_comparator_t</code></a>. This can also be a string view (C++17).</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>pos</code> (in)</dt> <dd>iterator to the element to remove</dd> <dt><code>first</code> (in)</dt> <dd>iterator to the beginning of the range to remove</dd> <dt><code>last</code> (in)</dt> <dd>iterator past the end of the range to remove</dd> <dt><code>key</code> (in)</dt> <dd>object key of the elements to remove</dd> <dt><code>idx</code> (in)</dt> <dd>array index of the element to remove</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <ol> <li>Iterator following the last removed element. If the iterator <code>pos</code> refers to the last element, the <code>end()</code> iterator is returned.</li> <li>Iterator following the last removed element. If the iterator <code>last</code> refers to the last element, the <code>end()</code> iterator is returned.</li> <li>Number of elements removed. If <code>ObjectType</code> is the default <code>std::map</code> type, the return value will always be <code>0</code> (<code>key</code> was not found) or <code>1</code> (<code>key</code> was found).</li> <li>See 3.</li> <li>(none)</li> </ol> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong exception safety: if an exception occurs, the original value stays intact.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <ol> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error307><code>type_error.307</code></a> if called on a <code>null</code> value; example: <code>"cannot use erase() with null"</code></li> <li>Throws <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator202><code>invalid_iterator.202</code></a> if called on an iterator which does not belong to the current <abbr title="JavaScript Object Notation">JSON</abbr> value; example: <code>"iterator does not fit current value"</code></li> <li>Throws <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator205><code>invalid_iterator.205</code></a> if called on a primitive type with invalid iterator (i.e., any iterator which is not <code>begin()</code>); example: <code>"iterator out of range"</code></li> </ul> </li> <li>The function can throw the following exceptions:<ul> <li>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error307><code>type_error.307</code></a> if called on a <code>null</code> value; example: <code>"cannot use erase() with null"</code></li> <li>Throws <a href=../../../home/exceptions/#jsoneLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -55,7 +55,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (2) remove elements given an iterator range</summary> <p>The example shows the effect of <code>erase()</code> for different <abbr title="JavaScript Object Notation">JSON</abbr> types using an iterator range.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (2) remove elements given an iterator range</summary> <p>The example shows the effect of <code>erase()</code> for different <abbr title="JavaScript Object Notation">JSON</abbr> types using an iterator range.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -92,7 +92,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (3) remove element from a <abbr title="JavaScript Object Notation">JSON</abbr> object given a key</summary> <p>The example shows the effect of <code>erase()</code> for different <abbr title="JavaScript Object Notation">JSON</abbr> types using an object key.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (3) remove element from a <abbr title="JavaScript Object Notation">JSON</abbr> object given a key</summary> <p>The example shows the effect of <code>erase()</code> for different <abbr title="JavaScript Object Notation">JSON</abbr> types using an object key.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -114,7 +114,7 @@
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=k>namespace</span><span class=w> </span><span class=nn>std</span><span class=o>::</span><span class=nn>string_view_literals</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -134,7 +134,7 @@
</code></pre></div> </details> <details class=example> <summary>Example: (5) remove element from a <abbr title="JavaScript Object Notation">JSON</abbr> array given an index</summary> <p>The example shows the effect of <code>erase()</code> using an array index.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> </details> <details class=example> <summary>Example: (5) remove element from a <abbr title="JavaScript Object Notation">JSON</abbr> array given an index</summary> <p>The example shows the effect of <code>erase()</code> using an array index.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
+5 -5
View File
@@ -113,7 +113,7 @@ The example shows the effect of `erase()` for different JSON types using an iter
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -162,7 +162,7 @@ The example shows the effect of `erase()` for different JSON types using an iter
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -211,7 +211,7 @@ The example shows the effect of `erase()` for different JSON types using an obje
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -245,7 +245,7 @@ The example shows the effect of `erase()` for different JSON types using an obje
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using namespace std::string_view_literals; using namespace std::string_view_literals;
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -277,7 +277,7 @@ The example shows the effect of `erase()` using an array index.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
+3 -3
View File
@@ -53,7 +53,7 @@ keep
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -61,11 +61,11 @@ keep
json j_invalid = "ä\xA9ü"; json j_invalid = "ä\xA9ü";
try try
{ {
std::cout << j_invalid.dump() << std::endl; std::cout << j_invalid.dump() << '\n';
} }
catch (const json::type_error& e) catch (const json::type_error& e)
{ {
std::cout << e.what() << std::endl; std::cout << e.what() << '\n';
} }
std::cout << "string with replaced invalid characters: " std::cout << "string with replaced invalid characters: "
+4 -4
View File
@@ -1,4 +1,4 @@
<!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/error_handler_t/" rel="canonical"><link href=../erase/ rel=prev><link href=../exception/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>error_handler_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/error_handler_t/" rel="canonical"><link href=../erase/ rel=prev><link href=../exception/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>error_handler_t - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> error_handler_t </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default 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12s-1.44-4.5-3.5-5.45C10.26 6.2 11.11 6 12 6a6 6 0 0 1 6 6 6 6 0 0 1-6 6m8-9.31V4h-4.69L12 .69 8.69 4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 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<span class=w> </span><span class=n>strict</span><span class=p>,</span> <span class=w> </span><span class=n>strict</span><span class=p>,</span>
<span class=w> </span><span class=n>replace</span><span class=p>,</span> <span class=w> </span><span class=n>replace</span><span class=p>,</span>
<span class=w> </span><span class=n>ignore</span><span class=p>,</span> <span class=w> </span><span class=n>ignore</span><span class=p>,</span>
@@ -7,7 +7,7 @@
</code></pre></div> <p>This enumeration is used to choose how to treat ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in a string value or object key:</p> <ul> <li><a href=../dump/ ><code>dump</code></a> uses it while serializing a <code>basic_json</code> value to text.</li> <li><a href=../to_cbor/ ><code>to_cbor</code></a>, <a href=../to_msgpack/ ><code>to_msgpack</code></a>, <a href=../to_ubjson/ ><code>to_ubjson</code></a>, <a href=../to_bjdata/ ><code>to_bjdata</code></a>, and <a href=../to_bson/ ><code>to_bson</code></a> use it while serializing a <code>basic_json</code> value to that binary format. Their default is <code>keep</code>, as no binary writer checked before this parameter was added. <abbr title="Concise Binary Object Representation">CBOR</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>, <abbr title="Binary JData">BJData</abbr>, and <abbr title="Binary JSON">BSON</abbr> require valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, so for these four the default is <code>strict</code> if <a href=../../macros/json_strict_binary_utf8/ ><code>JSON_STRICT_BINARY_UTF8</code></a> is enabled; MessagePack's specification explicitly allows a string to contain ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8, so <code>to_msgpack</code> stays at <code>keep</code>. <code>to_bon8</code> does not take this parameter: <abbr title="Binary Object Notation 8">BON8</abbr> always validates, since <abbr title="Unicode Transformation Format">UTF</abbr>-8 lead bytes are structural to that format.</li> <li><a href=../from_cbor/ ><code>from_cbor</code></a>, <a href=../from_msgpack/ ><code>from_msgpack</code></a>, <a href=../from_ubjson/ ><code>from_ubjson</code></a>, <a href=../from_bjdata/ ><code>from_bjdata</code></a>, and <a href=../from_bson/ ><code>from_bson</code></a> use it while parsing that binary format, to decide whether to check a string value or object key for well-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 at all; by default (<code>keep</code>) they do not, as no binary reader did before this parameter was added. <code>from_bon8</code> does not take this parameter, for the same reason <code>to_bon8</code> does not.</li> </ul> <p>Four values are differentiated:</p> <dl> <dt>strict</dt> <dd>throw a <code>type_error</code>/<code>parse_error</code> exception in case of invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</dd> <dt>replace</dt> <dd>replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD (� REPLACEMENT CHARACTER)</dd> <dt>ignore</dt> <dd>ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped</dd> <dt>keep</dt> <dd>keep invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences unchanged; only meaningful for the binary formats mentioned above, since <a href=../dump/ ><code>dump</code></a> itself must produce text, and <code>keep</code> there writes the ill-formed bytes to the output as is, so the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 (but still equals the input bytes exactly, including around any well-formed characters, which are still escaped as usual)</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how the different values of the <code>error_handler_t</code> influence the behavior of <a href=../dump/ ><code>dump</code></a> when reading serializing an invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequence.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> </code></pre></div> <p>This enumeration is used to choose how to treat ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 in a string value or object key:</p> <ul> <li><a href=../dump/ ><code>dump</code></a> uses it while serializing a <code>basic_json</code> value to text.</li> <li><a href=../to_cbor/ ><code>to_cbor</code></a>, <a href=../to_msgpack/ ><code>to_msgpack</code></a>, <a href=../to_ubjson/ ><code>to_ubjson</code></a>, <a href=../to_bjdata/ ><code>to_bjdata</code></a>, and <a href=../to_bson/ ><code>to_bson</code></a> use it while serializing a <code>basic_json</code> value to that binary format. Their default is <code>keep</code>, as no binary writer checked before this parameter was added. <abbr title="Concise Binary Object Representation">CBOR</abbr>, <abbr title="Universal Binary JSON">UBJSON</abbr>, <abbr title="Binary JData">BJData</abbr>, and <abbr title="Binary JSON">BSON</abbr> require valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, so for these four the default is <code>strict</code> if <a href=../../macros/json_strict_binary_utf8/ ><code>JSON_STRICT_BINARY_UTF8</code></a> is enabled; MessagePack's specification explicitly allows a string to contain ill-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8, so <code>to_msgpack</code> stays at <code>keep</code>. <code>to_bon8</code> does not take this parameter: <abbr title="Binary Object Notation 8">BON8</abbr> always validates, since <abbr title="Unicode Transformation Format">UTF</abbr>-8 lead bytes are structural to that format.</li> <li><a href=../from_cbor/ ><code>from_cbor</code></a>, <a href=../from_msgpack/ ><code>from_msgpack</code></a>, <a href=../from_ubjson/ ><code>from_ubjson</code></a>, <a href=../from_bjdata/ ><code>from_bjdata</code></a>, and <a href=../from_bson/ ><code>from_bson</code></a> use it while parsing that binary format, to decide whether to check a string value or object key for well-formed <abbr title="Unicode Transformation Format">UTF</abbr>-8 at all; by default (<code>keep</code>) they do not, as no binary reader did before this parameter was added. <code>from_bon8</code> does not take this parameter, for the same reason <code>to_bon8</code> does not.</li> </ul> <p>Four values are differentiated:</p> <dl> <dt>strict</dt> <dd>throw a <code>type_error</code>/<code>parse_error</code> exception in case of invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8</dd> <dt>replace</dt> <dd>replace invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences with U+FFFD (� REPLACEMENT CHARACTER)</dd> <dt>ignore</dt> <dd>ignore invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences; all valid bytes are copied to the output unchanged, and invalid bytes are dropped</dd> <dt>keep</dt> <dd>keep invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequences unchanged; only meaningful for the binary formats mentioned above, since <a href=../dump/ ><code>dump</code></a> itself must produce text, and <code>keep</code> there writes the ill-formed bytes to the output as is, so the result is then not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 (but still equals the input bytes exactly, including around any well-formed characters, which are still escaped as usual)</dd> </dl> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The example below shows how the different values of the <code>error_handler_t</code> influence the behavior of <a href=../dump/ ><code>dump</code></a> when reading serializing an invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 sequence.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -15,11 +15,11 @@
<span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_invalid</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"ä</span><span class=se>\xA9</span><span class=s>ü"</span><span class=p>;</span> <span class=w> </span><span class=n>json</span><span class=w> </span><span class=n>j_invalid</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=s>"ä</span><span class=se>\xA9</span><span class=s>ü"</span><span class=p>;</span>
<span class=w> </span><span class=k>try</span> <span class=w> </span><span class=k>try</span>
<span class=w> </span><span class=p>{</span> <span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_invalid</span><span class=p>.</span><span class=n>dump</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>j_invalid</span><span class=p>.</span><span class=n>dump</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span> <span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>type_error</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span> <span class=w> </span><span class=k>catch</span><span class=w> </span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>json</span><span class=o>::</span><span class=n>type_error</span><span class=o>&amp;</span><span class=w> </span><span class=n>e</span><span class=p>)</span>
<span class=w> </span><span class=p>{</span> <span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span> <span class=w> </span><span class=p>}</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"string with replaced invalid characters: "</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"string with replaced invalid characters: "</span>
+3 -3
View File
@@ -35,7 +35,7 @@ The example below shows how the different values of the `error_handler_t` influe
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -43,11 +43,11 @@ int main()
json j_invalid = "ä\xA9ü"; json j_invalid = "ä\xA9ü";
try try
{ {
std::cout << j_invalid.dump() << std::endl; std::cout << j_invalid.dump() << '\n';
} }
catch (const json::type_error& e) catch (const json::type_error& e)
{ {
std::cout << e.what() << std::endl; std::cout << e.what() << '\n';
} }
std::cout << "string with replaced invalid characters: " std::cout << "string with replaced invalid characters: "
+2 -2
View File
@@ -72,7 +72,7 @@ constructor.
#include <iostream> #include <iostream>
#include <nlohmann/json.hpp> #include <nlohmann/json.hpp>
using json = nlohmann::json; using nlohmann::json;
int main() int main()
{ {
@@ -86,7 +86,7 @@ constructor.
{ {
// output exception information // output exception information
std::cout << "message: " << e.what() << '\n' std::cout << "message: " << e.what() << '\n'
<< "exception id: " << e.id << std::endl; << "exception id: " << e.id << '\n';
} }
} }
+3 -3
View File
@@ -1,4 +1,4 @@
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1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"Line truncated <!doctype html><html lang=en class=no-js> <head><meta charset=utf-8><meta name=viewport content="width=device-width,initial-scale=1"><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json/exception/" rel="canonical"><link href=../error_handler_t/ rel=prev><link href=../find/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>exception - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet 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</code></pre></div> <p>This class is an extension of <a href="https://en.cppreference.com/w/cpp/error/exception"><code>std::exception</code></a> objects with a member <code>id</code> for exception ids. It is used as the base class for all exceptions thrown by the <code>basic_json</code> class. This class can hence be used as "wildcard" to catch exceptions, see example below.</p> <pre class=mermaid><code>classDiagram </code></pre></div> <p>This class is an extension of <a href="https://en.cppreference.com/w/cpp/error/exception"><code>std::exception</code></a> objects with a member <code>id</code> for exception ids. It is used as the base class for all exceptions thrown by the <code>basic_json</code> class. This class can hence be used as "wildcard" to catch exceptions, see example below.</p> <pre class=mermaid><code>classDiagram
direction LR direction LR
@@ -30,7 +30,7 @@
style json_exception fill:#CCCCFF</code></pre> <p>Subclasses:</p> <ul> <li><a href=../parse_error/ ><code>parse_error</code></a> for exceptions indicating a parse error</li> <li><a href=../invalid_iterator/ ><code>invalid_iterator</code></a> for exceptions indicating errors with iterators</li> <li><a href=../type_error/ ><code>type_error</code></a> for exceptions indicating executing a member function with a wrong type</li> <li><a href=../out_of_range/ ><code>out_of_range</code></a> for exceptions indicating access out of the defined range</li> <li><a href=../other_error/ ><code>other_error</code></a> for exceptions indicating other library errors</li> </ul> <h2 id=member-functions>Member functions<a class=headerlink href=#member-functions title="Permanent link">&para;</a></h2> <ul> <li><strong>what</strong> - returns explanatory string</li> </ul> <h2 id=member-variables>Member variables<a class=headerlink href=#member-variables title="Permanent link">&para;</a></h2> <ul> <li><strong>id</strong> - the id of the exception</li> </ul> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>To have nothrow-copy-constructible exceptions, we internally use <code>std::runtime_error</code> which can cope with arbitrary-length error messages. Intermediate strings are built with static functions and then passed to the actual constructor.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how arbitrary library exceptions can be caught.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span> style json_exception fill:#CCCCFF</code></pre> <p>Subclasses:</p> <ul> <li><a href=../parse_error/ ><code>parse_error</code></a> for exceptions indicating a parse error</li> <li><a href=../invalid_iterator/ ><code>invalid_iterator</code></a> for exceptions indicating errors with iterators</li> <li><a href=../type_error/ ><code>type_error</code></a> for exceptions indicating executing a member function with a wrong type</li> <li><a href=../out_of_range/ ><code>out_of_range</code></a> for exceptions indicating access out of the defined range</li> <li><a href=../other_error/ ><code>other_error</code></a> for exceptions indicating other library errors</li> </ul> <h2 id=member-functions>Member functions<a class=headerlink href=#member-functions title="Permanent link">&para;</a></h2> <ul> <li><strong>what</strong> - returns explanatory string</li> </ul> <h2 id=member-variables>Member variables<a class=headerlink href=#member-variables title="Permanent link">&para;</a></h2> <ul> <li><strong>id</strong> - the id of the exception</li> </ul> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>To have nothrow-copy-constructible exceptions, we internally use <code>std::runtime_error</code> which can cope with arbitrary-length error messages. Intermediate strings are built with static functions and then passed to the actual constructor.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Example</summary> <p>The following code shows how arbitrary library exceptions can be caught.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;iostream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span> <span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span> <span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span> <span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span> <span class=p>{</span>
@@ -44,7 +44,7 @@
<span class=w> </span><span class=p>{</span> <span class=w> </span><span class=p>{</span>
<span class=w> </span><span class=c1>// output exception information</span> <span class=w> </span><span class=c1>// output exception information</span>
<span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"message: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span> <span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>cout</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"message: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>what</span><span class=p>()</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span>
<span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"exception id: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>id</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=n>endl</span><span class=p>;</span> <span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=s>"exception id: "</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=n>e</span><span class=p>.</span><span class=n>id</span><span class=w> </span><span class=o>&lt;&lt;</span><span class=w> </span><span class=sc>'\n'</span><span class=p>;</span>
<span class=w> </span><span class=p>}</span> <span class=w> </span><span class=p>}</span>
<span class=p>}</span> <span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>message</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>403</span><span class=p>]</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=err>'</span><span class=kc>n</span><span class=err>o</span><span class=kc>n</span><span class=mf>-e</span><span class=err>xis</span><span class=kc>t</span><span class=err>i</span><span class=kc>n</span><span class=err>g'</span><span class=w> </span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=w> </span><span class=kc>f</span><span class=err>ou</span><span class=kc>n</span><span class=err>d</span> </code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=err>message</span><span class=p>:</span><span class=w> </span><span class=p>[</span><span class=err>jso</span><span class=kc>n</span><span class=err>.excep</span><span class=kc>t</span><span class=err>io</span><span class=kc>n</span><span class=err>.ou</span><span class=kc>t</span><span class=err>_o</span><span class=kc>f</span><span class=err>_ra</span><span class=kc>n</span><span class=err>ge.</span><span class=mi>403</span><span class=p>]</span><span class=w> </span><span class=err>key</span><span class=w> </span><span class=err>'</span><span class=kc>n</span><span class=err>o</span><span class=kc>n</span><span class=mf>-e</span><span class=err>xis</span><span class=kc>t</span><span class=err>i</span><span class=kc>n</span><span class=err>g'</span><span class=w> </span><span class=kc>n</span><span class=err>o</span><span class=kc>t</span><span class=w> </span><span class=kc>f</span><span class=err>ou</span><span class=kc>n</span><span class=err>d</span>
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