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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=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_view/dump/" rel="canonical"><link href=../count/ rel=prev><link href=../empty/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>dump - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_json_viewdump class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> dump </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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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=author content="Niels Lohmann"><link href="https://json.nlohmann.me/api/basic_json_view/dump/" rel="canonical"><link href=../count/ rel=prev><link href=../empty/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>dump - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new URL("../../..",location),__md_hash=e=>[...e].reduce(((e,_)=>(e<<5)-e+_.charCodeAt(0)),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script></head> <body dir=ltr data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo> <input class=md-toggle data-md-toggle=drawer type=checkbox id=__drawer autocomplete=off> <input class=md-toggle data-md-toggle=search type=checkbox id=__search autocomplete=off> <label class=md-overlay for=__drawer></label> <div data-md-component=skip> <a href=#nlohmannbasic_json_viewdump class=md-skip> Skip to content </a> </div> <div data-md-component=announce> </div> <header class=md-header data-md-component=header> <nav class="md-header__inner md-grid" aria-label=Header> <a href=../../.. title="JSON for Modern C++" class="md-header__button md-logo" aria-label="JSON for Modern C++" data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> dump </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark mode" 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12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.52 6.52 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5"/></svg> </label> <Line truncated
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>char</span><span class=w> </span><span class=n>indent_char</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=sc>' '</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=kt>bool</span><span class=w> </span><span class=n>ensure_ascii</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=nb>false</span><span class=p>,</span>
<span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>number_format</span><span class=w> </span><span class=n>numbers</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>number_format</span><span class=o>::</span><span class=n>shortest</span><span class=p>)</span><span class=w> </span><span class=k>const</span><span class=p>;</span>
</code></pre></div> <p>Serializes this value (and its subtree) directly from the flat index, without ever building a <code>BasicJsonType</code> value first. With the default <code class=highlight><span class=n>numbers</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>number_format</span><span class=o>::</span><span class=n>shortest</span></code>, the result is the same string <a href=../../basic_json/dump/ ><code>BasicJsonType::dump</code></a> would produce for the value <a href=../../basic_json/parse/ ><code>BasicJsonType::parse()</code></a> builds from the same source text, called with the same <code>indent</code>, <code>indent_char</code>, and <code>ensure_ascii</code> -- except that members of an object appear in document order rather than sorted by key, and <em>every</em> occurrence of a repeated key is written rather than only the last one (see <a href=../operator%5B%5D/#notes>Notes on duplicate keys</a>). For a <code>json_view</code> (whose <code>BasicJsonType</code> is not ordered), this means <code>dump()</code> can print an object's members in a different order than <a href=../materialize/ ><code>materialize()</code></a><code>.dump()</code> of the same subtree.</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">&para;</a></h2> <dl> <dt><code>indent</code> (in)</dt> <dd>If <code>indent</code> is nonnegative, array elements and object members are pretty-printed with that indent level. An indent level of <code>0</code> only inserts newlines. <code>-1</code> (the default) selects the most compact representation.</dd> <dt><code>indent_char</code> (in)</dt> <dd>The character used for indentation if <code>indent</code> is greater than <code>0</code>. The default is <code></code> (space).</dd> <dt><code>ensure_ascii</code> (in)</dt> <dd>If <code>ensure_ascii</code> is <code class=highlight><span class=nb>true</span></code>, all non-<abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters in the output are escaped with <code>\uXXXX</code> sequences, and the result consists of <abbr title="American Standard Code for Information Interchange">ASCII</abbr> characters only.</dd> <dt><code>numbers</code> (in)</dt> <dd>how to write numbers, see <a href=../number_format/ ><code>number_format</code></a>: <code>shortest</code> (the default) writes them the way <a href=../../basic_json/dump/ ><code>BasicJsonType::dump</code></a> would; <code>source</code> copies every number exactly as it appears in the source text.</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">&para;</a></h2> <p>string containing the serialization of this value, or <code class=highlight><span class=s>"&lt;discarded&gt;"</span></code> if the view 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>Strong exception safety: if an exception is thrown, there are no changes to the view or the document it refers to.</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 allocating the output string fails. Unlike <a href=../../basic_json/dump/ ><code>BasicJsonType::dump</code></a>, there is no <code>error_handler</code> parameter and no <a href=../../../home/exceptions/#jsonexceptiontype_error316><code>type_error.316</code></a>: the view only ever holds text the parser already validated as <abbr title="Unicode Transformation Format">UTF</abbr>-8, so there is nothing to replace or ignore.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">&para;</a></h2> <p>Linear in the size of the output text.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">&para;</a></h2> <p>The walk over the subtree is iterative, so the nesting depth it can write is limited by available memory only, not by the call stack -- as for <a href=../materialize/ ><code>materialize()</code></a>.</p> <p>Strings are escaped by the same rules as <a href=../../basic_json/dump/ ><code>BasicJsonType::dump</code></a>.</p> <p>With <code class=highlight><span class=n>numbers</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=n>number_format</span><span class=o>::</span><span class=n>shortest</span></code>, floats are written with the library's shortest round-trip conversion, exactly as <a href=../../basic_json/dump/ ><code>BasicJsonType::dump</code></a> would (e.g. <code class=highlight><span class=mf>1.5</span></code>, <code class=highlight><span class=mf>100.0</span></code>, <code class=highlight><span class=mf>1e+100</span></code>), and integers are copied from the source text -- already canonical in <abbr title="JavaScript Object Notation">JLine truncated
<span class=cp>#include</span><span class=w> </span><span class=cpf>&lt;nlohmann/json_view.hpp&gt;</span>
<span class=k>using</span><span class=w> </span><span class=n>json_document</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_document</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>json_view</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_view</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_document</span><span class=p>;</span>
<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json_view</span><span class=p>;</span>
<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
<span class=p>{</span>
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@@ -55,8 +55,8 @@ The example below forwards a single record out of a larger batch, and re-seriali
#include <iostream>
#include <nlohmann/json_view.hpp>
using json_document = nlohmann::json_document;
using json_view = nlohmann::json_view;
using nlohmann::json_document;
using nlohmann::json_view;
int main()
{