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<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/accept/" rel="canonical"><link href=../basic_json_document/ rel=prev><link href=../erase/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>accept - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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 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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/accept/" rel="canonical"><link href=../basic_json_document/ rel=prev><link href=../erase/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>accept - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet href=../../../css/fig-exceptions.css><link rel=stylesheet href=../../../css/fig-pointer.css><link rel=stylesheet href=../../../css/fig-charts.css><link rel=stylesheet href=../../../css/fig-integration.css><link rel=stylesheet href=../../../css/fig-macros.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=custom data-md-color-accent=custom> <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_json_documentaccept 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> <img src=../../../images/wordmark-header.svg alt=logo> </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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 dLine truncated
<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>input</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>
@@ -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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/basic_json_document/" rel="canonical"><link href=../ rel=prev><link href=../accept/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>(Constructor) - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet href=../../../css/fig-exceptions.css><link rel=stylesheet href=../../../css/fig-pointer.css><link rel=stylesheet href=../../../css/fig-charts.css><link rel=stylesheet href=../../../css/fig-integration.css><link rel=stylesheet href=../../../css/fig-macros.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=custom data-md-color-accent=custom> <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_json_documentbasic_json_document 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> <img src=../../../images/wordmark-header.svg alt=logo> </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> (Constructor) </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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 viewboLine 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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/basic_json_document/" rel="canonical"><link href=../ rel=prev><link href=../accept/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>(Constructor) - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet href=../../../css/fig-exceptions.css><link rel=stylesheet href=../../../css/fig-pointer.css><link rel=stylesheet href=../../../css/fig-charts.css><link rel=stylesheet href=../../../css/fig-integration.css><link rel=stylesheet href=../../../css/fig-macros.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=custom data-md-color-accent=custom> <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_json_documentbasic_json_document 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> <img src=../../../images/wordmark-header.svg alt=logo> </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> (Constructor) </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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 viewboLine truncated
<span class=n>basic_json_document</span><span class=p>()</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=k>default</span><span class=p>;</span>
<span class=c1>// (2)</span>
+1 -1
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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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/erase/" rel="canonical"><link href=../accept/ rel=prev><link href=../insert/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>erase - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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data-md-color-scheme=default data-md-color-primary=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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 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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 6.5Line truncated
<span class=n>std</span><span class=o>::</span><span class=kt>size_t</span><span class=w> </span><span class=nf>erase</span><span class=p>(</span><span class=n>view_type</span><span class=w> </span><span class=n>object</span><span class=p>,</span><span class=w> </span><span class=n>string_view_t</span><span class=w> </span><span class=n>key</span><span class=p>);</span>
<span class=c1>// (2)</span>
+2 -2
View File
@@ -1,3 +1,3 @@
<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/" rel="canonical"><link href=../basic_json/with_t/ rel=prev><link href=basic_json_document/ rel=next><link rel=icon href=../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>Overview - JSON for Modern C++</title><link rel=stylesheet href=../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../css/custom.css><link rel=stylesheet href=../../css/brand.css><link rel=stylesheet href=../../css/fig-sax.css><link rel=stylesheet href=../../css/fig-jsonview.css><link rel=stylesheet 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<span class=k>class</span><span class=w> </span><span class=nc>basic_json_document</span><span class=p>;</span>
</code></pre></div> <p>A parsed <abbr title="JavaScript Object Notation">JSON</abbr> text, held as a flat index of its values (<a href=../../home/architecture/#node-index-of-json-views>16 bytes per value</a>) instead of a tree of <code>BasicJsonType</code> values. Strings and floating-point numbers stay in the source text; integers are converted while parsing, and strings that contain escapes are decoded into one buffer owned by the document. <a href=../basic_json_view/ ><code>basic_json_view</code></a> is a read-only handle to one value of a <code>basic_json_document</code>; <a href=../basic_json_view/materialize/ ><code>materialize()</code></a> turns a subtree into the <code>BasicJsonType</code> value that <a href=../basic_json/parse/ ><code>BasicJsonType::parse()</code></a> would have produced for it.</p> <p>A document may <strong>borrow</strong> the text it was parsed from (the caller's buffer must then outlive the document) or <strong>own</strong> it (a copy, or an rvalue <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> that was moved in); see <a href=owns_source/ ><code>owns_source</code></a>. <code>basic_json_document</code> is move-only: a copy would duplicate the whole index, the decoded-string buffer, and the owned text, and a move is enough in every use we know of. The index, the decoded strings, and the owned text live in one heap block that the document holds through a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>unique_ptr</span></code>; this is also why views survive a move of the document.</p> <p>With <code class=highlight><span class=n>Mode</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>view_mode</span><span class=o>::</span><span class=n>editable</span></code>, the document also offers <a href=set/ ><code>set</code></a>, <a href=push_back/ ><code>push_back</code></a>, <a href=insert/ ><code>insert</code></a>, and <a href=erase/ ><code>erase</code></a> to change values in place, see <a href=#edits>Edits</a> below. The source text itself is never written; a read-only document (<code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>read_only</span></code>, the default) does not carry any of the bookkeeping edits need, and calling any of them on one fails to compile (<code class=highlight><span class=k>static_assert</span></code>).</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BasicJsonType</code></dt> <dd>a specialization of <a href=../basic_json/ ><code>basic_json</code></a>, for instance <a href=../json/ ><code>json</code></a> or <a href=../ordered_json/ ><code>ordered_json</code></a>. Only 64-bit <code>number_integer_t</code>/<code>number_unsigned_t</code> types are supported; this is checked with a <code>static_assert</code>.</dd> <dt><code>Mode</code></dt> <dd>a <a href=../view_mode/ ><code>view_mode</code></a>: <code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>editable</span></code> if the document supports <a href=set/ ><code>set</code></a>, <a href=push_back/ ><code>push_back</code></a>, <a href=insert/ ><code>insert</code></a>, and <a href=erase/ ><code>erase</code></a> (optional, <code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>read_only</span></code> by default). See <a href=#edits>Edits</a> below.</dd> </dl> <h2 id=specializations>Specializations<a class=headerlink href=#specializations title="Permanent link">&para;</a></h2> <ul> <li><a href=../json_document/ ><strong>json_document</strong></a> - read-only documents of the default specialization <a href=../json/ ><code>json</code></a></li> <li><a href=../ordered_json_document/ ><strong>ordered_json_document</strong></a> - read-only documents of <a href=../ordered_json/ ><code>ordered_json</code></a></li> <li><a href=../json_editable_document/ ><strong>json_editable_document</strong></a> - editable documents of <a href=../json/ ><code>json</code></a></li> <li><a href=../ordered_json_editable_document/ ><strong>ordered_json_editable_document</strong></a> - editable documents of <a href=../ordered_json/ ><code>ordered_json</code></a></li> </ul> <h2 id=member-types>Member types<a class=headerlink href=#member-types title="Permanent link">&para;</a></h2> <ul> <li><strong>view_type</strong> - the type of view returned by <a href=root/ ><code>root()</code></a> (<code class=highlight><span class=n>basic_json_view</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=n>Mode</span><span class=o>&gt;</span></code>)</li> <li><strong>value_t</strong> - the <abbr title="JavaScript Object Notation">JSON</abbr> type enumeration, see <a href=../basic_json/value_t/ ><code>basic_json::value_t</code></a></li> <li><strong>image_check</strongLine truncated
</code></pre></div> <p>A parsed <abbr title="JavaScript Object Notation">JSON</abbr> text, held as a flat index of its values (<a href=../../home/architecture/#node-index-of-json-views>16 bytes per value</a>) instead of a tree of <code>BasicJsonType</code> values. Strings and floating-point numbers stay in the source text; integers are converted while parsing, and strings that contain escapes are decoded into one buffer owned by the document. <a href=../basic_json_view/ ><code>basic_json_view</code></a> is a read-only handle to one value of a <code>basic_json_document</code>; <a href=../basic_json_view/materialize/ ><code>materialize()</code></a> turns a subtree into the <code>BasicJsonType</code> value that <a href=../basic_json/parse/ ><code>BasicJsonType::parse()</code></a> would have produced for it.</p> <p>A document may <strong>borrow</strong> the text it was parsed from (the caller's buffer must then outlive the document) or <strong>own</strong> it (a copy, or an rvalue <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> that was moved in); see <a href=owns_source/ ><code>owns_source</code></a>. <code>basic_json_document</code> is move-only: a copy would duplicate the whole index, the decoded-string buffer, and the owned text, and a move is enough in every use we know of. The index, the decoded strings, and the owned text live in one heap block that the document holds through a <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>unique_ptr</span></code>; this is also why views survive a move of the document.</p> <p>With <code class=highlight><span class=n>Mode</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>view_mode</span><span class=o>::</span><span class=n>editable</span></code>, the document also offers <a href=set/ ><code>set</code></a>, <a href=push_back/ ><code>push_back</code></a>, <a href=insert/ ><code>insert</code></a>, and <a href=erase/ ><code>erase</code></a> to change values in place, see <a href=#edits>Edits</a> below. The source text itself is never written; a read-only document (<code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>read_only</span></code>, the default) does not carry any of the bookkeeping edits need, and calling any of them on one fails to compile (<code class=highlight><span class=k>static_assert</span></code>).</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>BasicJsonType</code></dt> <dd>a specialization of <a href=../basic_json/ ><code>basic_json</code></a>, for instance <a href=../json/ ><code>json</code></a> or <a href=../ordered_json/ ><code>ordered_json</code></a>. Only 64-bit <code>number_integer_t</code>/<code>number_unsigned_t</code> types are supported; this is checked with a <code>static_assert</code>.</dd> <dt><code>Mode</code></dt> <dd>a <a href=../view_mode/ ><code>view_mode</code></a>: <code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>editable</span></code> if the document supports <a href=set/ ><code>set</code></a>, <a href=push_back/ ><code>push_back</code></a>, <a href=insert/ ><code>insert</code></a>, and <a href=erase/ ><code>erase</code></a> (optional, <code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>read_only</span></code> by default). See <a href=#edits>Edits</a> below.</dd> </dl> <h2 id=specializations>Specializations<a class=headerlink href=#specializations title="Permanent link">&para;</a></h2> <ul> <li><a href=../json_document/ ><strong>json_document</strong></a> - read-only documents of the default specialization <a href=../json/ ><code>json</code></a></li> <li><a href=../ordered_json_document/ ><strong>ordered_json_document</strong></a> - read-only documents of <a href=../ordered_json/ ><code>ordered_json</code></a></li> <li><a href=../json_editable_document/ ><strong>json_editable_document</strong></a> - editable documents of <a href=../json/ ><code>json</code></a></li> <li><a href=../ordered_json_editable_document/ ><strong>ordered_json_editable_document</strong></a> - editable documents of <a href=../ordered_json/ ><code>ordered_json</code></a></li> </ul> <h2 id=member-types>Member types<a class=headerlink href=#member-types title="Permanent link">&para;</a></h2> <ul> <li><strong>view_type</strong> - the type of view returned by <a href=root/ ><code>root()</code></a> (<code class=highlight><span class=n>basic_json_view</span><span class=o>&lt;</span><span class=n>BasicJsonType</span><span class=p>,</span><span class=w> </span><span class=n>Mode</span><span class=o>&gt;</span></code>)</li> <li><strong>value_t</strong> - the <abbr title="JavaScript Object Notation">JSON</abbr> type enumeration, see <a href=../basic_json/value_t/ ><code>basic_json::value_t</code></a></li> <li><strong>image_check</strongLine truncated
+1 -1
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@@ -73,7 +73,7 @@ An editable document (`view_mode::editable`) can be changed after parsing, with
- **A view keeps referring to the same value.** After [`set`](https://json.nlohmann.me/api/basic_json_document/set/index.md) replaces the value a view refers to, that view sees the new value; a view of a value that a later edit replaces or drops keeps showing what it last held. An edit of an array or object, however, **invalidates the iterators taken over it** (its members may now live in a different sequence), and a string obtained with [`get_string()`](https://json.nlohmann.me/api/basic_json_view/get_string/index.md) stays valid even as further edits happen (earlier buffers of edited text are kept alive, not overwritten).
- **Values are accepted three ways:** a [`basic_json_view`](https://json.nlohmann.me/api/basic_json_view/index.md) of *any* document (read-only or editable; it is copied, nothing is shared with the source document), a `BasicJsonType` value, or anything `BasicJsonType` can be constructed from (numbers, strings, `bool`, `nullptr`, containers, ...).
- [`dump()`](https://json.nlohmann.me/api/basic_json_view/dump/index.md) writes an edited document with members in document order, new members at the end, and, with [`number_format::source`](https://json.nlohmann.me/api/basic_json_view/number_format/index.md), keeps the spelling of every number that was not itself edited — see [Editing a document](https://json.nlohmann.me/features/json_view/editing/index.md) for why this matters.
- [`read()`](https://json.nlohmann.me/api/basic_json_document/read/index.md) discards all edits, [`shrink_to_fit()`](https://json.nlohmann.me/api/basic_json_document/shrink_to_fit/index.md) does not move the node index once there are edits, and [`memory_usage()`](https://json.nlohmann.me/api/basic_json_document/memory_usage/index.md) includes the memory edits use. [`source_offset()`](https://json.nlohmann.me/api/basic_json_view/source_offset/index.md) of a value introduced by an edit is `static_cast<std::size_t>(-1)`, the same value it reports for a decoded string.
- [`read()`](https://json.nlohmann.me/api/basic_json_document/read/index.md) discards all edits (so its `input` must not be a string obtained from this document), [`shrink_to_fit()`](https://json.nlohmann.me/api/basic_json_document/shrink_to_fit/index.md) does not move the node index once there are edits, and [`memory_usage()`](https://json.nlohmann.me/api/basic_json_document/memory_usage/index.md) includes the memory edits use. [`source_offset()`](https://json.nlohmann.me/api/basic_json_view/source_offset/index.md) of a value introduced by an edit is `static_cast<std::size_t>(-1)`, the same value it reports for a decoded string.
## See also
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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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/insert/" rel="canonical"><link href=../erase/ rel=prev><link href=../is_discarded/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>insert - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> insert </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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 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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/insert/" rel="canonical"><link href=../erase/ rel=prev><link href=../is_discarded/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>insert - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet href=../../../css/fig-exceptions.css><link rel=stylesheet href=../../../css/fig-pointer.css><link rel=stylesheet href=../../../css/fig-charts.css><link rel=stylesheet href=../../../css/fig-integration.css><link rel=stylesheet href=../../../css/fig-macros.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=custom data-md-color-accent=custom> <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_json_documentinsert 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> <img src=../../../images/wordmark-header.svg alt=logo> </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> insert </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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 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viewbox="0 0 24 24"><path d="M9.5 Line truncated
<span class=n>view_type</span><span class=w> </span><span class=n>insert</span><span class=p>(</span><span class=n>view_type</span><span class=w> </span><span class=n>array</span><span class=p>,</span><span class=w> </span><span class=n>I</span><span class=w> </span><span class=n>idx</span><span class=p>,</span><span class=w> </span><span class=n>V</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>value</span><span class=p>);</span>
</code></pre></div> <p>Only an <strong>editable</strong> document (<code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>editable</span></code>, e.g. <a href=../../json_editable_document/ ><code>json_editable_document</code></a>) has <code>insert</code>; calling it on a read-only <code>basic_json_document</code> fails to compile (<code class=highlight><span class=k>static_assert</span></code>).</p> <p>Inserts <code>value</code> into <code>array</code> as a new element before position <code>idx</code>, which must not be past the end (<code class=highlight><span class=n>idx</span><span class=w> </span><span class=o>&lt;=</span><span class=w> </span><span class=n>array</span><span class=p>.</span><span class=n>size</span><span class=p>()</span></code>; <code class=highlight><span class=n>idx</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>array</span><span class=p>.</span><span class=n>size</span><span class=p>()</span></code> appends, like <a href=../push_back/ ><code>push_back</code></a>). Unlike <a href=../push_back/ ><code>push_back</code></a>, a <a href=../../basic_json_view/is_null/ >null</a> <code>array</code> does <em>not</em> first become an empty array: <code>array</code> must already be an array.</p> <p><code>value</code> is accepted three ways: a <a href=../../basic_json_view/ ><code>basic_json_view</code></a> of <em>any</em> document — read-only or editable, and it does not have to be <code>array</code>'s own document — which is copied so that nothing is shared with the source document afterward; a <code>BasicJsonType</code> value; or anything <code>BasicJsonType</code> can be constructed from (numbers, strings, <code class=highlight><span class=kt>bool</span></code>, <code class=highlight><span class=nb>nullptr</span></code>, containers, ...).</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>I</code></dt> <dd>an integral type other than <code class=highlight><span class=kt>bool</span></code>, deduced (overloads taking a <code class=highlight><span class=kt>bool</span></code> or a non-integral type for <code>idx</code> do not participate in overload resolution).</dd> <dt><code>V</code></dt> <dd>the type of <code>value</code>, deduced; see above for what is accepted.</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>array</code> (in)</dt> <dd>the array to insert into</dd> <dt><code>idx</code> (in)</dt> <dd>the position to insert <code>value</code> before; a negative value throws (see <a href=#exceptions>Exceptions</a>)</dd> <dt><code>value</code> (in)</dt> <dd>the value to insert</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>a view of the new element, now holding <code>value</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Basic exception safety: <code>value</code> is fully encoded — including the checks below — into storage owned by the document before anything already reachable from <a href=../root/ ><code>root()</code></a> is touched, so a failure while encoding <code>value</code> (an invalid argument, or <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>bad_alloc</span></code>) leaves the document completely unchanged, other than memory allocated for the encoding that is not reclaimed. A failure of a later allocation — while <code>array</code> switches from its parsed layout to a growable block, or while that block grows, see <a href=#notes>Notes</a> — can still leave <code>array</code> already switched to that layout even though <code>value</code> itself was not inserted.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error309><code>type_error.309</code></a> if <code>array</code> is not an array — the same message <a href=../../basic_json/insert/ ><code>BasicJsonType::insert</code></a> throws for the same type; a null <code>array</code> throws this too (see above). Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range401><code>out_of_range.401</code></a> if <code>idx</code> is negative, or if <code class=highlight><span class=n>idx</span><span class=w> </span><span class=o>&gt;</span><span class=w> </span><span class=n>array</span><span class=p>.</span><span class=n>size</span><span class=p>()</span></code>. Throws <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator202><code>invalid_iterator.202</code></a> ("view does not belong to this document") if <code>array</code> is a <a href=../../basic_json_view/is_discarded/ >discarded</a> view or a view of a <em>different</em> document. Throws <aLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
@@ -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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/is_discarded/" rel="canonical"><link href=../insert/ rel=prev><link href=../load/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>is_discarded - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> is_discarded </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: 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<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/is_discarded/" rel="canonical"><link href=../insert/ rel=prev><link href=../load/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>is_discarded - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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</code></pre></div> <p>Returns whether the document holds no value, either because it was default-constructed or because the last call to <a href=../parse/ ><code>parse()</code></a>, <a href=../parse_copy/ ><code>parse_copy()</code></a>, or <a href=../read/ ><code>read()</code></a> failed with <code>allow_exceptions</code> set to <code class=highlight><span class=nb>false</span></code>.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the document is discarded, <code class=highlight><span class=nb>false</span></code> 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 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>When the document is discarded, <a href=../root/ ><code>root()</code></a> returns a discarded view (its <a href=../../basic_json_view/is_discarded/ ><code>is_discarded()</code></a> is also <code class=highlight><span class=nb>true</span></code>).</p> <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>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
+6 -5
View File
@@ -113,11 +113,12 @@ How thoroughly `load()` validates `image` before trusting it.
`full` (the default)
: Checks everything the parser itself guarantees: structure and bounds; that every string is valid UTF-8 (and, for a
string still in the source text, that it contains no quote, backslash, or control character); and that every number
token is well-formed and matches the value stored for it. Strings and float tokens may share a range only if the
ranges are identical (as nodes that share a value do), and never overlap otherwise. Reading and serializing a
checked image is safe and always produces valid JSON, exactly as for a parsed document. This is the right choice for
an image from anything you do not fully control — a file, a cache shared with other processes, a peer on the
network.
token is well-formed and matches the value stored for it, and has the type the parser gives it (a float node only
for a token with a fraction or an exponent, or an integer that does not fit 64 bits). Strings and float tokens may
share a range only if the ranges are identical (as nodes that share a value do), and never overlap otherwise.
Reading and serializing a checked image is safe and always produces valid JSON, exactly as for a parsed document.
This is the right choice for an image from anything you do not fully control — a file, a cache shared with other
processes, a peer on the network.
`bounds`
: Checks structure and bounds only: that every offset and count in the node index stays inside the image. So
+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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/load/" rel="canonical"><link href=../is_discarded/ rel=prev><link href=../memory_usage/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>load - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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<span class=k>static</span><span class=w> </span><span class=n>basic_json_document</span><span class=w> </span><span class=nf>load</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>std</span><span class=o>::</span><span class=kt>uint8_t</span><span class=o>*</span><span class=w> </span><span class=n>image</span><span class=p>,</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=n>size</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>image_check</span><span class=w> </span><span class=n>check</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>image_check</span><span class=o>::</span><span class=n>full</span><span class=p>);</span>
@@ -21,7 +21,7 @@
<span class=w> </span><span class=n>bounds</span><span class=p>,</span>
<span class=w> </span><span class=n>none</span>
<span class=p>};</span>
</code></pre></div> <p>How thoroughly <code>load()</code> validates <code>image</code> before trusting it.</p> <dl> <dt><code>full</code> (the default)</dt> <dd>Checks everything the parser itself guarantees: structure and bounds; that every string is valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 (and, for a string still in the source text, that it contains no quote, backslash, or control character); and that every number token is well-formed and matches the value stored for it. Strings and float tokens may share a range only if the ranges are identical (as nodes that share a value do), and never overlap otherwise. Reading and serializing a checked image is safe and always produces valid <abbr title="JavaScript Object Notation">JSON</abbr>, exactly as for a parsed document. This is the right choice for an image from anything you do not fully control — a file, a cache shared with other processes, a peer on the network.</dd> <dt><code>bounds</code></dt> <dd>Checks structure and bounds only: that every offset and count in the node index stays inside the image. So <code>load()</code>, <a href=../root/ ><code>root()</code></a>, element access, and <a href=../../basic_json_view/materialize/ ><code>materialize()</code></a> can never read outside the image, even on a damaged one. It does <em>not</em> guarantee that the image describes valid <abbr title="JavaScript Object Notation">JSON</abbr>: a string that a <code>full</code> check would have rejected can make <a href=../../basic_json_view/dump/ ><code>dump()</code></a> write invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 or invalid <abbr title="JavaScript Object Notation">JSON</abbr>, or throw <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a>, and a number can read back with a value that does not match how it is spelled. An <a href=../../json_editable_document/ >editable document</a> does not take such a string over: <a href=../set/ ><code>set</code></a>, <a href=../push_back/ ><code>push_back</code></a> and <a href=../insert/ ><code>insert</code></a> throw <code>type_error.316</code> when they copy it from a view of the loaded document, and leave the editable document unchanged. <code>bounds</code> skips scanning the text and the decoded strings, so it fits a cache your own process just wrote and reads straight back, where damage would mean a bug or a hardware fault rather than adversarial input.</dd> <dt><code>none</code></dt> <dd>Checks nothing. Reading a damaged image is undefined behavior, so use it only for an image you trust as much as your own memory.</dd> </dl> <p><strong>Lifetime.</strong> Overloads 1 and 2 borrow <code>image</code>: it must stay alive and byte-for-byte unchanged for as long as the returned document, and any <a href=../../basic_json_view/ >view</a> taken from it, is used — exactly like a document <a href=../parse/ ><code>parse()</code></a> borrowed its input for. Overload 3 avoids this by keeping the vector itself; see <a href=../owns_source/ ><code>owns_source</code></a>.</p> <div class="admonition warning"> <p class=admonition-title>Experimental</p> <p>The image format is versioned but not yet stable, and may change in an incompatible way before it is declared stable; <code>load()</code> already rejects an image written by a different format version with <code>parse_error.116</code> ("unknown format"). Use images to cache a document within one build of the library, or to hand one to another process running the <em>same</em> build on the <em>same</em> (little-endian) machine — not as a long-term storage format.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Caching a document, ownership, and a rejected image</summary> <p>The example below saves a parsed document as an image, checks that <code>load()</code> reproduces the original <a href=../../basic_json_view/dump/ ><code>dump()</code></a> without parsing, and shows the difference between <code>load(std::move(image))</code> (owned) and <code>load(image)</code> (borrowed). It then damages one byte of the image and shows <code>image_check::full</code> rejecting it with <code>parse_error.116</code>, while <code>image_check::bounds</code> — meant for a cache the process already trusts — still reads it without going out of bounds.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;cstdint&gt;</span>
</code></pre></div> <p>How thoroughly <code>load()</code> validates <code>image</code> before trusting it.</p> <dl> <dt><code>full</code> (the default)</dt> <dd>Checks everything the parser itself guarantees: structure and bounds; that every string is valid <abbr title="Unicode Transformation Format">UTF</abbr>-8 (and, for a string still in the source text, that it contains no quote, backslash, or control character); and that every number token is well-formed and matches the value stored for it, and has the type the parser gives it (a float node only for a token with a fraction or an exponent, or an integer that does not fit 64 bits). Strings and float tokens may share a range only if the ranges are identical (as nodes that share a value do), and never overlap otherwise. Reading and serializing a checked image is safe and always produces valid <abbr title="JavaScript Object Notation">JSON</abbr>, exactly as for a parsed document. This is the right choice for an image from anything you do not fully control — a file, a cache shared with other processes, a peer on the network.</dd> <dt><code>bounds</code></dt> <dd>Checks structure and bounds only: that every offset and count in the node index stays inside the image. So <code>load()</code>, <a href=../root/ ><code>root()</code></a>, element access, and <a href=../../basic_json_view/materialize/ ><code>materialize()</code></a> can never read outside the image, even on a damaged one. It does <em>not</em> guarantee that the image describes valid <abbr title="JavaScript Object Notation">JSON</abbr>: a string that a <code>full</code> check would have rejected can make <a href=../../basic_json_view/dump/ ><code>dump()</code></a> write invalid <abbr title="Unicode Transformation Format">UTF</abbr>-8 or invalid <abbr title="JavaScript Object Notation">JSON</abbr>, or throw <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a>, and a number can read back with a value that does not match how it is spelled. An <a href=../../json_editable_document/ >editable document</a> does not take such a string over: <a href=../set/ ><code>set</code></a>, <a href=../push_back/ ><code>push_back</code></a> and <a href=../insert/ ><code>insert</code></a> throw <code>type_error.316</code> when they copy it from a view of the loaded document, and leave the editable document unchanged. <code>bounds</code> skips scanning the text and the decoded strings, so it fits a cache your own process just wrote and reads straight back, where damage would mean a bug or a hardware fault rather than adversarial input.</dd> <dt><code>none</code></dt> <dd>Checks nothing. Reading a damaged image is undefined behavior, so use it only for an image you trust as much as your own memory.</dd> </dl> <p><strong>Lifetime.</strong> Overloads 1 and 2 borrow <code>image</code>: it must stay alive and byte-for-byte unchanged for as long as the returned document, and any <a href=../../basic_json_view/ >view</a> taken from it, is used — exactly like a document <a href=../parse/ ><code>parse()</code></a> borrowed its input for. Overload 3 avoids this by keeping the vector itself; see <a href=../owns_source/ ><code>owns_source</code></a>.</p> <div class="admonition warning"> <p class=admonition-title>Experimental</p> <p>The image format is versioned but not yet stable, and may change in an incompatible way before it is declared stable; <code>load()</code> already rejects an image written by a different format version with <code>parse_error.116</code> ("unknown format"). Use images to cache a document within one build of the library, or to hand one to another process running the <em>same</em> build on the <em>same</em> (little-endian) machine — not as a long-term storage format.</p> </div> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Caching a document, ownership, and a rejected image</summary> <p>The example below saves a parsed document as an image, checks that <code>load()</code> reproduces the original <a href=../../basic_json_view/dump/ ><code>dump()</code></a> without parsing, and shows the difference between <code>load(std::move(image))</code> (owned) and <code>load(image)</code> (borrowed). It then damages one byte of the image and shows <code>image_check::full</code> rejecting it with <code>parse_error.116</code>, while <code>image_check::bounds</code> — meant for a cache the process already trusts — still reads it without going out of bounds.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;cstdint&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;string&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;vector&gt;</span>
@@ -78,4 +78,4 @@
<span class=kc>true</span>
<span class=mi>116</span>
<span class=err>cache</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=../save/ ><code>save</code></a> - write the document as an image</li> <li><a href=../owns_source/ ><code>owns_source</code></a> - return whether the document holds its own copy of the text</li> <li><a href=../parse/ ><code>parse</code></a> - deserialize from <abbr title="JavaScript Object Notation">JSON</abbr> text instead of an image</li> <li><a href=../../../features/json_view/images/ >Images</a> - why and when to use images</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 3.13.0 <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="November 9, 2026 07:12:00 UTC">November 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../is_discarded/ class="md-footer__link md-footer__link--prev" aria-label="Previous: is_discarded"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> is_discarded </div> </div> </a> <a href=../memory_usage/ class="md-footer__link md-footer__link--next" aria-label="Next: memory_usage"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> memory_usage </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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</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=../save/ ><code>save</code></a> - write the document as an image</li> <li><a href=../owns_source/ ><code>owns_source</code></a> - return whether the document holds its own copy of the text</li> <li><a href=../parse/ ><code>parse</code></a> - deserialize from <abbr title="JavaScript Object Notation">JSON</abbr> text instead of an image</li> <li><a href=../../../features/json_view/images/ >Images</a> - why and when to use images</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 3.13.0 <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="November 11, 2026 21:36:54 UTC">November 11, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../is_discarded/ class="md-footer__link md-footer__link--prev" aria-label="Previous: is_discarded"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> is_discarded </div> </div> </a> <a href=../memory_usage/ class="md-footer__link md-footer__link--next" aria-label="Next: memory_usage"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> memory_usage </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+1 -1
View File
@@ -92,7 +92,7 @@ enum class image_check
How thoroughly `load()` validates `image` before trusting it.
`full` (the default) : Checks everything the parser itself guarantees: structure and bounds; that every string is valid UTF-8 (and, for a string still in the source text, that it contains no quote, backslash, or control character); and that every number token is well-formed and matches the value stored for it. Strings and float tokens may share a range only if the ranges are identical (as nodes that share a value do), and never overlap otherwise. Reading and serializing a checked image is safe and always produces valid JSON, exactly as for a parsed document. This is the right choice for an image from anything you do not fully control — a file, a cache shared with other processes, a peer on the network.
`full` (the default) : Checks everything the parser itself guarantees: structure and bounds; that every string is valid UTF-8 (and, for a string still in the source text, that it contains no quote, backslash, or control character); and that every number token is well-formed and matches the value stored for it, and has the type the parser gives it (a float node only for a token with a fraction or an exponent, or an integer that does not fit 64 bits). Strings and float tokens may share a range only if the ranges are identical (as nodes that share a value do), and never overlap otherwise. Reading and serializing a checked image is safe and always produces valid JSON, exactly as for a parsed document. This is the right choice for an image from anything you do not fully control — a file, a cache shared with other processes, a peer on the network.
`bounds` : Checks structure and bounds only: that every offset and count in the node index stays inside the image. So `load()`, [`root()`](https://json.nlohmann.me/api/basic_json_document/root/index.md), element access, and [`materialize()`](https://json.nlohmann.me/api/basic_json_view/materialize/index.md) can never read outside the image, even on a damaged one. It does *not* guarantee that the image describes valid JSON: a string that a `full` check would have rejected can make [`dump()`](https://json.nlohmann.me/api/basic_json_view/dump/index.md) write invalid UTF-8 or invalid JSON, or throw [`type_error.316`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error316), and a number can read back with a value that does not match how it is spelled. An [editable document](https://json.nlohmann.me/api/json_editable_document/index.md) does not take such a string over: [`set`](https://json.nlohmann.me/api/basic_json_document/set/index.md), [`push_back`](https://json.nlohmann.me/api/basic_json_document/push_back/index.md) and [`insert`](https://json.nlohmann.me/api/basic_json_document/insert/index.md) throw `type_error.316` when they copy it from a view of the loaded document, and leave the editable document unchanged. `bounds` skips scanning the text and the decoded strings, so it fits a cache your own process just wrote and reads straight back, where damage would mean a bug or a hardware fault rather than adversarial input.
@@ -1,4 +1,4 @@
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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> memory_usage </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: 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xmlns=http://www.w3.org/2000/svg viewbox="0 0 Line truncated
</code></pre></div> <p>Returns the number of bytes held by the document: the node index, the decoded-string buffer (for strings that contain escapes), and, for an owned document, its copy of the source text.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The number of bytes the document holds, <code>0</code> for a <a href=../is_discarded/ >discarded</a> document.</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 exact value depends on the platform, the allocator, and the library's own layout, and may change between versions; do not rely on it being a specific number, and do not compare it across different builds or platforms. Compare it for the same document over time, or between documents built with the same binary, instead — for instance to observe the effect of <a href=../shrink_to_fit/ ><code>shrink_to_fit()</code></a>.</p> <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>
<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_view.hpp&gt;</span>
@@ -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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/node_count/" rel="canonical"><link href=../memory_usage/ rel=prev><link href=../owns_source/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>node_count - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/node_count/" rel="canonical"><link href=../memory_usage/ rel=prev><link href=../owns_source/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>node_count - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> node_count </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)" 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viewbox="0 0Line truncated
</code></pre></div> <p>Returns the number of entries in the document's flat index.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The number of index entries: one per value (of any type, at any nesting depth) plus one per object key. <code>0</code> for a <a href=../is_discarded/ >discarded</a> document.</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>Each index entry is <a href=../../../home/architecture/#node-index-of-json-views>16 bytes</a>, so <code class=highlight><span class=n>node_count</span><span class=p>()</span><span class=w> </span><span class=o>*</span><span class=w> </span><span class=mi>16</span></code> is the size of the index itself (part, but not all, of <a href=../memory_usage/ ><code>memory_usage()</code></a>, which also counts decoded strings and, for an owned document, the text).</p> <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>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
@@ -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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/owns_source/" rel="canonical"><link href=../node_count/ rel=prev><link href=../parse/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>owns_source - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> owns_source </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: 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</code></pre></div> <p>Returns whether the document holds its own copy of the parsed text or is borrowing the caller's buffer.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p><code class=highlight><span class=nb>true</span></code> if the document owns the text returned by <a href=../source/ ><code>source()</code></a>, <code class=highlight><span class=nb>false</span></code> if it borrows it (or if the document is <a href=../is_discarded/ >discarded</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>See the ownership table on <a href=../parse/#notes><code>parse</code></a> for which inputs are borrowed and which are owned. A borrowed document (<code class=highlight><span class=n>owns_source</span><span class=p>()</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=nb>false</span></code>) is only valid while the buffer it was parsed from is still alive.</p> <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>
<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_view.hpp&gt;</span>
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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>static</span><span class=w> </span><span class=n>basic_json_document</span><span class=w> </span><span class=n>parse</span><span class=p>(</span><span class=n>InputType</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>input</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>allow_exceptions</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</span><span class=p>,</span>
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<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/parse_copy/" rel="canonical"><link href=../parse/ rel=prev><link href=../push_back/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>parse_copy - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> parse_copy </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)" 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<span class=k>static</span><span class=w> </span><span class=n>basic_json_document</span><span class=w> </span><span class=n>parse_copy</span><span class=p>(</span><span class=n>InputType</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>input</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>allow_exceptions</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</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>
+1 -1
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<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/push_back/" rel="canonical"><link href=../parse_copy/ rel=prev><link href=../read/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>push_back - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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viewbox="0 0 24 24"><pathLine truncated
<span class=n>view_type</span><span class=w> </span><span class=n>push_back</span><span class=p>(</span><span class=n>view_type</span><span class=w> </span><span class=n>array</span><span class=p>,</span><span class=w> </span><span class=n>V</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>value</span><span class=p>);</span>
</code></pre></div> <p>Appends <code>value</code> as a new last element of <code>array</code>. A <a href=../../basic_json_view/is_null/ >null</a> <code>array</code> first becomes an empty array, the same way <a href=../set/ ><code>set</code></a> turns a null <code>object</code> into an empty object.</p> <p><code>value</code> is accepted three ways: a <a href=../../basic_json_view/ ><code>basic_json_view</code></a> of <em>any</em> document — read-only or editable, and it does not have to be <code>array</code>'s own document — which is copied so that nothing is shared with the source document afterward; a <code>BasicJsonType</code> value; or anything <code>BasicJsonType</code> can be constructed from (numbers, strings, <code class=highlight><span class=kt>bool</span></code>, <code class=highlight><span class=nb>nullptr</span></code>, containers, ...).</p> <p>Only an <strong>editable</strong> document (<code class=highlight><span class=n>view_mode</span><span class=o>::</span><span class=n>editable</span></code>, e.g. <a href=../../json_editable_document/ ><code>json_editable_document</code></a>) has <code>push_back</code>; calling it on a read-only <code>basic_json_document</code> fails to compile (<code class=highlight><span class=k>static_assert</span></code>).</p> <h2 id=template-parameters>Template parameters<a class=headerlink href=#template-parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>V</code></dt> <dd>the type of <code>value</code>, deduced; see above for what is accepted.</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>array</code> (in)</dt> <dd>the array (or null value) to append to</dd> <dt><code>value</code> (in)</dt> <dd>the value to append</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>a view of the new last element of <code>array</code>, now holding <code>value</code></p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Basic exception safety: <code>value</code> is fully encoded — including the checks below — into storage owned by the document before anything already reachable from <a href=../root/ ><code>root()</code></a> is touched, so a failure while encoding <code>value</code> (an invalid argument, or <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>bad_alloc</span></code>) leaves the document completely unchanged, other than memory allocated for the encoding that is not reclaimed. A failure of a later allocation — while <code>array</code> switches from its parsed layout to a growable block, or while that block grows, see <a href=#notes>Notes</a> — can still leave a partial effect, such as a null <code>array</code> argument already turned into an empty array even though <code>value</code> itself was not appended.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error308><code>type_error.308</code></a> if <code>array</code> is neither an array nor null — the same message <a href=../../basic_json/push_back/ ><code>BasicJsonType::push_back</code></a> throws for the same type. Throws <a href=../../../home/exceptions/#jsonexceptioninvalid_iterator202><code>invalid_iterator.202</code></a> ("view does not belong to this document") if <code>array</code> is a <a href=../../basic_json_view/is_discarded/ >discarded</a> view or a view of a <em>different</em> document. Throws <a href=../../../home/exceptions/#jsonexceptiontype_error302><code>type_error.302</code></a> if <code>value</code> is a <a href=../../basic_json_view/is_discarded/ >discarded</a> view or a <a href=../../basic_json/is_discarded/ >discarded</a> <code>BasicJsonType</code> value, and <a href=../../../home/exceptions/#jsonexceptiontype_error319><code>type_error.319</code></a> if <code>value</code> is (or contains) a binary value — <code>BasicJsonType</code> can hold one, but a <code>json_document</code> cannot. Throws <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a> if <code>value</code> is (or contains) a string that is not valid <abbr title="Unicode Transformation Format">UTF</abbr>-8, with the same message <a href=../../basic_json/dump/ ><code>BasicJsonType::dump()</code></a> gives for that string.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Amortized constant, plus time linear in the size of <code>value</code> to encode it into the document's storage (constant for a scalar, linear in the number of nested values for an array or object): the elements of <code>array</code> move to a growable block of links the first time it is appended to (or <a href=../set/ ><code>set</code></a> on), and that block itself grLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
+28
View File
@@ -46,6 +46,34 @@ Linear in the length of the input.
Every view taken from `#!cpp *this` before the call — including the previous [`root()`](root.md) — is invalidated,
whether or not the new parse succeeds; take fresh views from [`root()`](root.md) afterward.
!!! warning "`input` must not point into the document itself"
`read()` releases the document's previous text, its decoded strings, and (for an editable document) its edits
*before* it parses `input`. An `input` that is, or points into, any of them violates a precondition: it may seem to
work, parse empty or garbled text, be reported by a sanitizer, or read freed memory (undefined behavior).
This applies to every `string_view` obtained from the document whose characters live in memory that `read()`
releases:
- [`source()`](source.md) of a document that owns its text;
- [`get_string()`](../basic_json_view/get_string.md) (also as `get<string_view_t>()` or a `string_view` member of a
decoded struct) of a string with escapes, of a string of a document that owns its text, and of an edited string;
- [`number_token()`](../basic_json_view/number_token.md) of a number of a document that owns its text, and of a
number written by an edit;
- the key of an object member (`key()`) if it has escapes, was written by an edit, or the document owns its text.
It does not apply to a text that the caller owns and the document borrows, nor to the strings, keys, and tokens that
are read from such a text unchanged, nor to the decoded strings of a borrowed [image](load.md), which live in the
caller's image: `read()` never touches them. To parse JSON that a document holds in a string of its own (for
example, JSON embedded in a string value), copy the string first, for example with
`#!cpp std::string inner(doc.root()["payload"].get_string()); doc.read(inner);`.
A debug build (one without `NDEBUG`) checks this with `assert()`: an `input` in the document's text, decoded
strings, or image, or in the most recent buffer of strings written by edits, ends the program. (Strings written
by earlier edits are not covered.) A release build does not check, to keep the cost of reusing a document at a
minimum. The check uses `assert()` directly, not [`JSON_ASSERT`](../macros/json_assert.md), which `json.hpp`
undefines at its end.
`input` is borrowed or owned by the same rules as [`parse()`](parse.md#notes); a document can borrow on one call and
own on the next, since ownership is decided freshly each time. An input that is copied (see the table in
[`parse()`](parse.md#notes)) is written into the document's previous owned copy, reusing its memory; a moved-in
+3 -3
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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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/read/" rel="canonical"><link href=../push_back/ rel=prev><link href=../root/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>read - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> read </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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0 24 24"><path d="M9.5 3A6.5 6.5 0 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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/read/" rel="canonical"><link href=../push_back/ rel=prev><link href=../root/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>read - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet href=../../../css/fig-exceptions.css><link rel=stylesheet href=../../../css/fig-pointer.css><link rel=stylesheet href=../../../css/fig-charts.css><link rel=stylesheet href=../../../css/fig-integration.css><link rel=stylesheet href=../../../css/fig-macros.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=custom data-md-color-accent=custom> <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_json_documentread 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> <img src=../../../images/wordmark-header.svg alt=logo> </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> read </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=kt>void</span><span class=w> </span><span class=n>read</span><span class=p>(</span><span class=n>InputType</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>input</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>allow_exceptions</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>true</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>
</code></pre></div> <p>(Re-)parses <code>input</code> into <code class=highlight><span class=o>*</span><span class=k>this</span></code>, discarding the document's previous value and reusing its memory (the node index, the decoded-string buffer, and, if applicable, the owned copy of the text) rather than allocating a fresh document. <a href=../parse/ ><code>parse()</code></a> is implemented in terms of this function, applied to a default-constructed document.</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>A compatible input; see <a href=../parse/#template-parameters><code>parse</code></a>.</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>input</code> (in)</dt> <dd>Input to parse from.</dd> <dt><code>allow_exceptions</code> (in)</dt> <dd>whether to throw exceptions in case of a parse error (optional, <code class=highlight><span class=nb>true</span></code> by default)</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> </dl> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Same as <a href=../parse/#exceptions><code>parse</code></a>.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the length of the input.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Every view taken from <code class=highlight><span class=o>*</span><span class=k>this</span></code> before the call — including the previous <a href=../root/ ><code>root()</code></a> — is invalidated, whether or not the new parse succeeds; take fresh views from <a href=../root/ ><code>root()</code></a> afterward.</p> <p><code>input</code> is borrowed or owned by the same rules as <a href=../parse/#notes><code>parse()</code></a>; a document can borrow on one call and own on the next, since ownership is decided freshly each time. An input that is copied (see the table in <a href=../parse/#notes><code>parse()</code></a>) is written into the document's previous owned copy, reusing its memory; a moved-in <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span></code> replaces it.</p> <p>Reusing a document matters most for large inputs: the operating system provides the memory of a fresh node index one page at a time, and every page costs a page fault the first time it is written. On x86-64 Linux (4 KiB pages), parsing a 55 MB document into a reused document took about 40 % less time than parsing it into a fresh one. Programs that parse many documents of similar size should therefore keep one document and call <code>read()</code>.</p> <p>An integer argument that is not a <code class=highlight><span class=kt>bool</span></code> where the flags are expected, such as <code class=highlight><span class=n>read</span><span class=p>(</span><span class=n>ptr</span><span class=p>,</span><span class=w> </span><span class=n>len</span><span class=p>)</span></code>, does not compile; see <a href=../parse/#notes><code>parse</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 parses a sequence of messages into the same document, reusing its memory instead of allocating a new document for each one.</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>(Re-)parses <code>input</code> into <code class=highlight><span class=o>*</span><span class=k>this</span></code>, discarding the document's previous value and reusing its memory (the node index, the decoded-string buffer, and, if applicable, the owned copy of the text) rather than allocating a fresh document. <a href=../parse/ ><code>parse()</code></a> is implemented in terms of this function, applied to a default-constructed document.</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>A compatible input; see <a href=../parse/#template-parameters><code>parse</code></a>.</dd> </dl> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>input</code> (in)</dt> <dd>Input to parse from.</dd> <dt><code>allow_exceptions</code> (in)</dt> <dd>whether to throw exceptions in case of a parse error (optional, <code class=highlight><span class=nb>true</span></code> by default)</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> </dl> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Same as <a href=../parse/#exceptions><code>parse</code></a>.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the length of the input.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>Every view taken from <code class=highlight><span class=o>*</span><span class=k>this</span></code> before the call — including the previous <a href=../root/ ><code>root()</code></a> — is invalidated, whether or not the new parse succeeds; take fresh views from <a href=../root/ ><code>root()</code></a> afterward.</p> <div class="admonition warning"> <p class=admonition-title><code>input</code> must not point into the document itself</p> <p><code>read()</code> releases the document's previous text, its decoded strings, and (for an editable document) its edits <em>before</em> it parses <code>input</code>. An <code>input</code> that is, or points into, any of them violates a precondition: it may seem to work, parse empty or garbled text, be reported by a sanitizer, or read freed memory (undefined behavior).</p> <p>This applies to every <code>string_view</code> obtained from the document whose characters live in memory that <code>read()</code> releases:</p> <ul> <li><a href=../source/ ><code>source()</code></a> of a document that owns its text;</li> <li><a href=../../basic_json_view/get_string/ ><code>get_string()</code></a> (also as <code>get&lt;string_view_t&gt;()</code> or a <code>string_view</code> member of a decoded struct) of a string with escapes, of a string of a document that owns its text, and of an edited string;</li> <li><a href=../../basic_json_view/number_token/ ><code>number_token()</code></a> of a number of a document that owns its text, and of a number written by an edit;</li> <li>the key of an object member (<code>key()</code>) if it has escapes, was written by an edit, or the document owns its text.</li> </ul> <p>It does not apply to a text that the caller owns and the document borrows, nor to the strings, keys, and tokens that are read from such a text unchanged, nor to the decoded strings of a borrowed <a href=../load/ >image</a>, which live in the caller's image: <code>read()</code> never touches them. To parse <abbr title="JavaScript Object Notation">JSON</abbr> that a document holds in a string of its own (for example, <abbr title="JavaScript Object Notation">JSON</abbr> embedded in a string value), copy the string first, for example with <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string</span><span class=w> </span><span class=n>inner</span><span class=p>(</span><span class=n>doc</span><span class=p>.</span><span class=n>root</span><span class=p>()[</span><span class=s>"payload"</span><span class=p>].</span><span class=n>get_string</span><span class=p>());</span><span class=w> </span><span class=n>doc</span><span class=p>.</span><span class=n>read</span><span class=p>(</span><span class=n>inner</span><span class=p>);</span></code>.</p> <p>A debug build (one without <codeLine truncated
<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;vector&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
@@ -36,4 +36,4 @@
<span class=p>}</span>
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=mi>4</span>
<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=../parse/ ><code>parse</code></a> - deserialize from a compatible input</li> <li><a href=../root/ ><code>root</code></a> - the view of the root value</li> <li><a href=../load/ ><code>load</code></a> - read a document from an image instead of parsing <abbr title="JavaScript Object Notation">JSON</abbr> text</li> <li><a href=../../../features/json_view/lifetime/ >Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views</a> - reusing a document and what it invalidates</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 3.13.0 <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="November 9, 2026 07:12:00 UTC">November 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../push_back/ class="md-footer__link md-footer__link--prev" aria-label="Previous: push_back"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> push_back </div> </div> </a> <a href=../root/ class="md-footer__link md-footer__link--next" aria-label="Next: root"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> root </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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</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/ ><code>parse</code></a> - deserialize from a compatible input</li> <li><a href=../root/ ><code>root</code></a> - the view of the root value</li> <li><a href=../load/ ><code>load</code></a> - read a document from an image instead of parsing <abbr title="JavaScript Object Notation">JSON</abbr> text</li> <li><a href=../../../features/json_view/lifetime/ >Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views</a> - reusing a document and what it invalidates</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 3.13.0 <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="November 11, 2026 21:36:17 UTC">November 11, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../push_back/ class="md-footer__link md-footer__link--prev" aria-label="Previous: push_back"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> push_back </div> </div> </a> <a href=../root/ class="md-footer__link md-footer__link--next" aria-label="Next: root"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> root </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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+15
View File
@@ -36,6 +36,21 @@ Linear in the length of the input.
Every view taken from `*this` before the call — including the previous [`root()`](https://json.nlohmann.me/api/basic_json_document/root/index.md) — is invalidated, whether or not the new parse succeeds; take fresh views from [`root()`](https://json.nlohmann.me/api/basic_json_document/root/index.md) afterward.
`input` must not point into the document itself
`read()` releases the document's previous text, its decoded strings, and (for an editable document) its edits *before* it parses `input`. An `input` that is, or points into, any of them violates a precondition: it may seem to work, parse empty or garbled text, be reported by a sanitizer, or read freed memory (undefined behavior).
This applies to every `string_view` obtained from the document whose characters live in memory that `read()` releases:
- [`source()`](https://json.nlohmann.me/api/basic_json_document/source/index.md) of a document that owns its text;
- [`get_string()`](https://json.nlohmann.me/api/basic_json_view/get_string/index.md) (also as `get<string_view_t>()` or a `string_view` member of a decoded struct) of a string with escapes, of a string of a document that owns its text, and of an edited string;
- [`number_token()`](https://json.nlohmann.me/api/basic_json_view/number_token/index.md) of a number of a document that owns its text, and of a number written by an edit;
- the key of an object member (`key()`) if it has escapes, was written by an edit, or the document owns its text.
It does not apply to a text that the caller owns and the document borrows, nor to the strings, keys, and tokens that are read from such a text unchanged, nor to the decoded strings of a borrowed [image](https://json.nlohmann.me/api/basic_json_document/load/index.md), which live in the caller's image: `read()` never touches them. To parse JSON that a document holds in a string of its own (for example, JSON embedded in a string value), copy the string first, for example with `std::string inner(doc.root()["payload"].get_string()); doc.read(inner);`.
A debug build (one without `NDEBUG`) checks this with `assert()`: an `input` in the document's text, decoded strings, or image, or in the most recent buffer of strings written by edits, ends the program. (Strings written by earlier edits are not covered.) A release build does not check, to keep the cost of reusing a document at a minimum. The check uses `assert()` directly, not [`JSON_ASSERT`](https://json.nlohmann.me/api/macros/json_assert/index.md), which `json.hpp` undefines at its end.
`input` is borrowed or owned by the same rules as [`parse()`](https://json.nlohmann.me/api/basic_json_document/parse/#notes); a document can borrow on one call and own on the next, since ownership is decided freshly each time. An input that is copied (see the table in [`parse()`](https://json.nlohmann.me/api/basic_json_document/parse/#notes)) is written into the document's previous owned copy, reusing its memory; a moved-in `std::string` replaces it.
Reusing a document matters most for large inputs: the operating system provides the memory of a fresh node index one page at a time, and every page costs a page fault the first time it is written. On x86-64 Linux (4 KiB pages), parsing a 55 MB document into a reused document took about 40 % less time than parsing it into a fresh one. Programs that parse many documents of similar size should therefore keep one document and call `read()`.
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<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/root/" rel="canonical"><link href=../read/ rel=prev><link href=../save/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>root - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet 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<span class=n>view_type</span><span class=w> </span><span class=nf>root</span><span class=p>()</span><span class=w> </span><span class=k>const</span><span class=o>&amp;</span><span class=w> </span><span class=k>noexcept</span><span class=p>;</span>
<span class=c1>// (2)</span>
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</code></pre></div> <p>Writes the document as an <em>image</em>: a byte buffer that <a href=../load/ ><code>load</code></a> reads back without parsing. The image holds the node index, the source text (plus, for an edited document, the number tokens edits wrote), and the decoded strings (plus the strings edits wrote) — everything <a href=../root/ ><code>root()</code></a> needs, with nothing left to parse.</p> <p>An edited document is written in its <em>current</em> state, with its values in document order, the way the library's own parser would have produced them for that <abbr title="JavaScript Object Notation">JSON</abbr> text: a member <a href=../set/ ><code>set</code></a> added goes at the end, an <a href=../erase/ ><code>erase</code></a>d member leaves no trace, and a float that is not finite (<abbr title="Not a Number">NaN</abbr> or positive/negative infinity) becomes null, the same substitution <a href=../../basic_json_view/dump/ ><code>dump()</code></a> makes. The same document always saves to the same bytes — also across <code>BasicJsonType</code> and the <a href=../../view_mode/ ><code>view_mode</code></a>, since the image reflects document order and values only, not which specialization produced them.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>The image, as 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>. Pass it, or a pointer to its data together with its size, to <a href=../load/ ><code>load</code></a> to read the document back.</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">&para;</a></h2> <p>Strong guarantee: <code>save()</code> does not modify <code class=highlight><span class=o>*</span><span class=k>this</span></code> (it is <code class=highlight><span class=k>const</span></code>), so if it throws, the document is left exactly as it was, and the partially built image is discarded with the exception.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>Throws <a href=../../../home/exceptions/#jsonexceptiontype_error320><code>type_error.320</code></a> if the document is <a href=../is_discarded/ >discarded</a> — a default-constructed document, or one a failed <a href=../parse/ ><code>parse()</code></a>/ <a href=../read/ ><code>read()</code></a> with <code>allow_exceptions == false</code> left discarded.</p> <p>Throws <a href=../../../home/exceptions/#jsonexceptionout_of_range416><code>out_of_range.416</code></a> if the node count, the text, or the decoded strings of the image would individually reach 4 <abbr title="Gibibyte (2^30 bytes)">GiB</abbr> — the same 32-bit offsets <a href=../parse/#exceptions><code>parse()</code></a> and, for edits, <a href=../set/ ><code>set</code></a>/<a href=../push_back/ ><code>push_back</code></a> are already limited to.</p> <div class="admonition failure"> <p class=admonition-title>Example messages</p> <p><div class=highlight><pre><span></span><code>[json.exception.type_error.320] cannot save a discarded json_document
</code></pre></div> <div class=highlight><pre><span></span><code>[json.exception.out_of_range.416] images of 4 GiB or more are not supported by json_document
</code></pre></div></p> </div> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of the document: the number of nodes, plus the length of the text and the decoded strings that end up in the image.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p><strong>Format.</strong> The image begins with a 64-byte header (the magic bytes <code class=highlight><span class=s>"NJVI"</span></code>, a version number, the node count, and the sizes of the text and the decoded strings, all little-endian), followed by the nodes (<a href=../../../home/architecture/#node-index-of-json-views>16 bytes each</a>), the text and a <code class=highlight><span class=sc>'\0'</span></code>, and the decoded strings and a <code class=highlight><span class=sc>'\0'</span></code>. <a href=../load/ ><code>load</code></a> checks the header, and the sizes it describes, before reading anything else — see <a href=../load/#exceptions><code>load</code>'s Exceptions</a>.</p> <div class="admonition warning"> <p class=admonition-title>Experimental</p> <p>The image format is versioned but not yet stable: it may change in an incompatible way before it is declared stable. Use images to cache a document within one build of the library, or to hand one to another process running the <em>same</em> build on the <em>same</em> (little-endian) machine — not as a long-term storage format. Keep the original <abbr title="JavaScript Object Notation">JSON</abbr> text if you need to read a saved document back with a future library version.</p> </div> <p><strong>Little-endian targets only.</strong> The image is written as raw little-endian bytes, with no byte-swapping. On a big-endian target, <code>save()</code> and <a href=../load/ ><code>load</code></a> do not exist: a call fails to compile rather than produce bytes a big-endian reader could not interpret correctly.</p> <h2 id=examples>Examples<a class=headerlink href=#examples title="Permanent link">&para;</a></h2> <details class=example> <summary>Caching a parsed document as an image</summary> <p>The example below saves a parsed configuration as an image — the way a service might cache one to answer later requests without parsing the text again — and confirms that loading it back gives exactly the same result as parsing did, and that saving is deterministic.</p> <div class=highlight><pre><span></span><code><span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;cstdint&gt;</span>
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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>V</span><span class=o>&gt;</span>
<span class=n>view_type</span><span class=w> </span><span class=n>set</span><span class=p>(</span><span class=n>view_type</span><span class=w> </span><span class=n>target</span><span class=p>,</span><span class=w> </span><span class=n>V</span><span class=o>&amp;&amp;</span><span class=w> </span><span class=n>value</span><span class=p>);</span>
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<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/shrink_to_fit/" rel="canonical"><link href=../set/ rel=prev><link href=../source/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>shrink_to_fit - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> shrink_to_fit </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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 2Line truncated
</code></pre></div> <p>Releases capacity that is no longer needed, both of the node index and of the buffer for decoded strings (strings that contained escape sequences), e.g. after <a href=../read/ ><code>read()</code></a> replaced a large document with a much smaller one. Like <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>::</span><span class=n>shrink_to_fit</span><span class=p>()</span></code>, this is a non-binding request: the library may keep more capacity than strictly necessary.</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 the document.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">&para;</a></h2> <p>May throw <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>bad_alloc</span></code> if the reallocation fails; on exception, the document is unchanged.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in <a href=../node_count/ ><code>node_count()</code></a> plus the length of the decoded strings.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>The node index of a small document (an estimate of up to 1024 nodes, which is up to about 4 KiB of minified text) is allocated together with the document's header, so that parsing needs one allocation. That part cannot be released separately: <code>shrink_to_fit()</code> only trims a node index that has its own allocation, and the decoded strings.</p> <div class="admonition warning"> <p class=admonition-title>Invalidates views</p> <p>Unlike moving the document, <code>shrink_to_fit()</code> <strong>invalidates every view taken from this document before the call</strong>, including a previously obtained <a href=../root/ ><code>root()</code></a>: the node index is moved into a new, smaller allocation, and the old one is freed. Take a fresh view from <a href=../root/ ><code>root()</code></a> after calling this function.</p> </div> <p>This is unlike <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>vector</span><span class=o>::</span><span class=n>shrink_to_fit</span><span class=p>()</span></code>, which promises nothing about validity but in practice often leaves iterators alone when it did not need to reallocate; here, an implementation that avoids a reallocation when possible would be an internal optimization only, not a guarantee to rely on.</p> <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>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;sstream&gt;</span>
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;string&gt;</span>
+3
View File
@@ -24,6 +24,9 @@ Constant.
For a borrowed document, `source()` points directly into the caller's buffer, so it is only valid while that buffer
is; see [`owns_source`](owns_source.md).
The text of a document that owns it must not be passed to [`read()`](read.md) of the same document: `read()` releases
an owned text before it parses its input. Copy it first. (A borrowed text belongs to the caller and is not affected.)
## Examples
??? example
+3 -3
View File
@@ -1,5 +1,5 @@
<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/source/" rel="canonical"><link href=../shrink_to_fit/ rel=prev><link href=../../basic_json_view/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>source - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link 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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> <img src=../../../images/wordmark-header.svg alt=logo> </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> source </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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">Line truncated
</code></pre></div> <p>Returns the parsed text, whether it is borrowed from the caller or owned by the document.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>A <code class=highlight><span class=n>string_view_t</span></code> (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string_view</span></code> on C++17 and newer) over the parsed text, or an empty one if the document is <a href=../is_discarded/ >discarded</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>For a borrowed document, <code>source()</code> points directly into the caller's buffer, so it is only valid while that buffer is; see <a href=../owns_source/ ><code>owns_source</code></a>.</p> <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>
<!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=description content="JSON for Modern C++ is a header-only C++11 library that makes JSON a first-class data type."><meta name=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_document/source/" rel="canonical"><link href=../shrink_to_fit/ rel=prev><link href=../../basic_json_view/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.8.0"><title>source - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.57a0d79d.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.fb2fffe2.min.css><link rel=stylesheet href=../../../css/custom.css><link rel=stylesheet href=../../../css/brand.css><link rel=stylesheet href=../../../css/fig-sax.css><link rel=stylesheet href=../../../css/fig-jsonview.css><link rel=stylesheet href=../../../css/fig-exceptions.css><link rel=stylesheet href=../../../css/fig-pointer.css><link rel=stylesheet href=../../../css/fig-charts.css><link rel=stylesheet href=../../../css/fig-integration.css><link rel=stylesheet href=../../../css/fig-macros.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=custom data-md-color-accent=custom> <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_json_documentsource 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> <img src=../../../images/wordmark-header.svg alt=logo> </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> source </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=custom data-md-color-accent=custom 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=custom data-md-color-accent=custom 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">Line truncated
</code></pre></div> <p>Returns the parsed text, whether it is borrowed from the caller or owned by the document.</p> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>A <code class=highlight><span class=n>string_view_t</span></code> (<code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>string_view</span></code> on C++17 and newer) over the parsed text, or an empty one if the document is <a href=../is_discarded/ >discarded</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>For a borrowed document, <code>source()</code> points directly into the caller's buffer, so it is only valid while that buffer is; see <a href=../owns_source/ ><code>owns_source</code></a>.</p> <p>The text of a document that owns it must not be passed to <a href=../read/ ><code>read()</code></a> of the same document: <code>read()</code> releases an owned text before it parses its input. Copy it first. (A borrowed text belongs to the caller and is not affected.)</p> <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>
<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_view.hpp&gt;</span>
@@ -22,4 +22,4 @@
</code></pre></div> <p>Output:</p> <div class=highlight><pre><span></span><code><span class=kc>true</span>
<span class=p>{</span><span class=nt>"a"</span><span class=p>:</span><span class=w> </span><span class=mi>1</span><span class=p>}</span>
<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=../owns_source/ ><code>owns_source</code></a> - return whether the document holds its own copy of the text</li> <li><a href=../../basic_json_view/source_offset/ ><code>source_offset</code></a> - byte offset of a value in the source text</li> <li><a href=../../../features/json_view/lifetime/ >Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views</a> - who owns the source text and for how long</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 3.13.0 <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="November 9, 2026 07:12:00 UTC">November 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../shrink_to_fit/ class="md-footer__link md-footer__link--prev" aria-label="Previous: shrink_to_fit"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> shrink_to_fit </div> </div> </a> <a href=../../basic_json_view/ class="md-footer__link md-footer__link--next" aria-label="Next: Overview"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> Overview </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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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</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=../owns_source/ ><code>owns_source</code></a> - return whether the document holds its own copy of the text</li> <li><a href=../../basic_json_view/source_offset/ ><code>source_offset</code></a> - byte offset of a value in the source text</li> <li><a href=../../../features/json_view/lifetime/ >Zero-copy <abbr title="JavaScript Object Notation">JSON</abbr> views</a> - who owns the source text and for how long</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 3.13.0 <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="November 11, 2026 21:36:17 UTC">November 11, 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> <nav class="md-footer__inner md-grid" aria-label=Footer> <a href=../shrink_to_fit/ class="md-footer__link md-footer__link--prev" aria-label="Previous: shrink_to_fit"> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11z"/></svg> </div> <div class=md-footer__title> <span class=md-footer__direction> Previous </span> <div class=md-ellipsis> shrink_to_fit </div> </div> </a> <a href=../../basic_json_view/ class="md-footer__link md-footer__link--next" aria-label="Next: Overview"> <div class=md-footer__title> <span class=md-footer__direction> Next </span> <div class=md-ellipsis> Overview </div> </div> <div class="md-footer__button md-icon"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M4 11v2h12l-5.5 5.5 1.42 1.42L19.84 12l-7.92-7.92L10.5 5.5 16 11z"/></svg> </div> </a> </nav> <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
View File
@@ -22,6 +22,8 @@ Constant.
For a borrowed document, `source()` points directly into the caller's buffer, so it is only valid while that buffer is; see [`owns_source`](https://json.nlohmann.me/api/basic_json_document/owns_source/index.md).
The text of a document that owns it must not be passed to [`read()`](https://json.nlohmann.me/api/basic_json_document/read/index.md) of the same document: `read()` releases an owned text before it parses its input. Copy it first. (A borrowed text belongs to the caller and is not affected.)
## Examples
Example