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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/operator_eq/" rel="canonical"><link href=../operator%5B%5D/ rel=prev><link href=../operator_ne/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>operator== - JSON for Modern C++</title><link rel=stylesheet href=../../../assets/stylesheets/main.ec1eaa64.min.css><link rel=stylesheet href=../../../assets/stylesheets/palette.ab4e12ef.min.css><link rel="stylesheet" href="../../../assets/external/fonts.googleapis.com/css.61a430c9.css"><style>:root{--md-text-font:"Roboto";--md-code-font:"JetBrains Mono"}</style><link rel=stylesheet href=../../../css/custom.css><script>__md_scope=new 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data-md-component=logo> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M12 8a3 3 0 0 0 3-3 3 3 0 0 0-3-3 3 3 0 0 0-3 3 3 3 0 0 0 3 3m0 3.54C9.64 9.35 6.5 8 3 8v11c3.5 0 6.64 1.35 9 3.54 2.36-2.19 5.5-3.54 9-3.54V8c-3.5 0-6.64 1.35-9 3.54"/></svg> </a> <label class="md-header__button md-icon" for=__drawer> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M3 6h18v2H3zm0 5h18v2H3zm0 5h18v2H3z"/></svg> </label> <div class=md-header__title data-md-component=header-title> <div class=md-header__ellipsis> <div class=md-header__topic> <span class=md-ellipsis> JSON for Modern C++ </span> </div> <div class=md-header__topic data-md-component=header-topic> <span class=md-ellipsis> operator== </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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<!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/operator_eq/" rel="canonical"><link href=../operator%5B%5D/ rel=prev><link href=../operator_ne/ rel=next><link rel=icon href=../../../assets/images/favicon.png><meta name=generator content="mkdocs-1.6.1, mkdocs-material-9.7.7"><title>operator== - 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_viewoperator 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> operator== </span> </div> </div> </div> <form class=md-header__option data-md-component=palette> <input class=md-option data-md-color-media="(prefers-color-scheme: light)" data-md-color-scheme=default data-md-color-primary=indigo data-md-color-accent=indigo aria-label="Switch to dark 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4H4v4.69L.69 12 4 15.31V20h4.69L12 23.31 15.31 20H20v-4.69L23.31 12z"/></svg> </label> </form> <script>var palette=__md_get("__palette");if(palette&&palette.color){if("(prefers-color-scheme)"===palette.color.media){var media=matchMedia("(prefers-color-scheme: light)"),input=document.querySelector(media.matches?"[data-md-color-media='(prefers-color-scheme: light)']":"[data-md-color-media='(prefers-color-scheme: dark)']");palette.color.media=input.getAttribute("data-md-color-media"),palette.color.scheme=input.getAttribute("data-md-color-scheme"),palette.color.primary=input.getAttribute("data-md-color-primary"),palette.color.accent=input.getAttribute("data-md-color-accent")}for(var[key,value]of Object.entries(palette.color))document.body.setAttribute("data-md-color-"+key,value)}</script> <label class="md-header__button md-icon" for=__search> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 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<span class=kt>bool</span><span class=w> </span><span class=k>operator</span><span class=o>==</span><span class=p>(</span><span class=k>const</span><span class=w> </span><span class=n>basic_json_view</span><span class=o>&</span><span class=w> </span><span class=n>lhs</span><span class=p>,</span><span class=w> </span><span class=k>const</span><span class=w> </span><span class=n>basic_json_view</span><span class=o>&</span><span class=w> </span><span class=n>rhs</span><span class=p>);</span>
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<span class=c1>// (2)</span>
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</code></pre></div> <ol> <li>Compares two views for equality: whether the values <a href=../../basic_json/parse/ ><code>BasicJsonType::parse()</code></a> would produce for <code>lhs</code> and <code>rhs</code> are equal, according to <code>BasicJsonType</code>'s <a href=../../basic_json/operator_eq/ ><code>operator==</code></a>.</li> <li>Compares a view and a <code>BasicJsonType</code> value for equality, in either order: whether the value <code>parse()</code> would produce for the view and the other operand are equal, according to <code>BasicJsonType</code>'s <a href=../../basic_json/operator_eq/ ><code>operator==</code></a>.</li> </ol> <p>Neither overload builds a <code>BasicJsonType</code> value for a view to do the comparison (see <a href=#notes>Notes</a> below). Numbers compare by value across their types (<code class=highlight><span class=mi>1</span><span class=w> </span><span class=o>==</span><span class=w> </span><span class=mf>1.0</span></code>), and an object compares by its members, with duplicate keys resolved exactly as <code>parse()</code> resolves them -- the last value, at the position of the first occurrence of the key. This is not what <a href=../operator%5B%5D/ ><code>operator[]</code></a> and the other lookups return for a duplicate key: they find the <em>first</em> member (see <a href=../../../features/json_view/#duplicate-keys>Duplicate keys</a>).</p> <h2 id=parameters>Parameters<a class=headerlink href=#parameters title="Permanent link">¶</a></h2> <dl> <dt><code>lhs</code> (in)</dt> <dd>first value to consider</dd> <dt><code>rhs</code> (in)</dt> <dd>second value to consider</dd> </dl> <h2 id=return-value>Return value<a class=headerlink href=#return-value title="Permanent link">¶</a></h2> <p>whether the values <code>lhs</code> and <code>rhs</code> are equal</p> <h2 id=exception-safety>Exception safety<a class=headerlink href=#exception-safety title="Permanent link">¶</a></h2> <p>Strong exception safety: if an exception is thrown, there are no changes to either operand, or to the document(s) a view refers to.</p> <h2 id=exceptions>Exceptions<a class=headerlink href=#exceptions title="Permanent link">¶</a></h2> <p>May throw <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>bad_alloc</span></code>. Unlike the other comparison and most other <code>basic_json_view</code> functions, <code>operator==</code> is not <code class=highlight><span class=k>noexcept</span></code>: resolving an object's members needs a temporary array to sort them by key (see <a href=#complexity>Complexity</a> below), and that allocation can fail.</p> <h2 id=complexity>Complexity<a class=headerlink href=#complexity title="Permanent link">¶</a></h2> <p>Linear in the size of the compared values: every number, string, array element, and object member is visited at most once, and the walk is iterative, so the nesting depth it can compare is limited by available memory only, not by the call stack (as for <a href=../materialize/ ><code>materialize()</code></a>). Resolving an object's members takes an additional O(n log n) in the number of members at that level, since they are sorted by key to detect and resolve duplicates before being compared. Two arrays of different <a href=../size/ ><code>size()</code></a> are rejected without visiting either one's elements.</p> <h2 id=notes>Notes<a class=headerlink href=#notes title="Permanent link">¶</a></h2> <p>Only a single number, boolean, or <code class=highlight><span class=n>null</span></code> value is ever materialized into a <code>BasicJsonType</code>, to reuse its <code>operator==</code> -- for numbers, so that values written differently in the source text but equal in value (e.g. an integer and a floating-point literal) still compare equal, following the same rules <code>BasicJsonType</code> does for special values such as <code class=highlight><span class=n>NaN</span></code>. Constructing one of these scalars never allocates. Strings are compared directly, without allocating, either from the source text on both sides or, for overload 2, against <code>BasicJsonType</code>'s own string. Arrays and objects are never materialized at all; only their elements or members are visited, one pair at a time.</p> <div class="admonition info"> <p class=admonition-title>How objects are compared</p> <p>For a <a href=../../json_view/ ><code>json_view</code></a> (<code>BasicJsonType::object_t</code> is <code class=highlight><span class=n>std</span><span class=o>::</span><span class=n>map</span></code>), members are compared by key, regardless of the order they appear in the source text. For an <a href=../../ordered_json_view/ ><code>ordered_json_view</code></a> (<code>object_t</code> is <code>ordered_map</code>), they are compared in the order they occur, so the very same two objects with their members reordered can compare equal as <code>json_view</code>s but not as <code>ordered_json_view</code>s. This is exactly how <a href=..Line truncated
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<span class=cp>#include</span><span class=w> </span><span class=cpf><nlohmann/json_view.hpp></span>
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<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>
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<span class=k>using</span><span class=w> </span><span class=n>json</span><span class=w> </span><span class=o>=</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
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<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>
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<span class=k>using</span><span class=w> </span><span class=n>nlohmann</span><span class=o>::</span><span class=n>json</span><span class=p>;</span>
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<span class=kt>int</span><span class=w> </span><span class=nf>main</span><span class=p>()</span>
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<span class=p>{</span>
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