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<body>
<div class="highlight highlight-source-c++"><pre>    #<span class="pl-k">include</span> <span class="pl-s"><span class="pl-pds">"</span>jsoncons/json.hpp<span class="pl-pds">"</span></span>

    <span class="pl-k">using</span> jsoncons::json;
    <span class="pl-k">using</span> jsoncons::pretty_print;</pre></div>

<h2>Constructing a json value</h2>

<h3>From a string</h3>

<div class="highlight highlight-source-c++"><pre>    std::string input = R<span class="pl-s"><span class="pl-pds">"</span>(</span>
<span class="pl-s">    {</span>
<span class="pl-s">        <span class="pl-pds">"</span></span>first_name<span class="pl-s"><span class="pl-pds">"</span>:<span class="pl-pds">"</span></span>Jane<span class="pl-s"><span class="pl-pds">"</span>,</span>
<span class="pl-s">        <span class="pl-pds">"</span></span>last_name<span class="pl-s"><span class="pl-pds">"</span>:<span class="pl-pds">"</span></span>Roe<span class="pl-s"><span class="pl-pds">"</span>,</span>
<span class="pl-s">        <span class="pl-pds">"</span></span>events_attended<span class="pl-s"><span class="pl-pds">"</span>:10</span>
<span class="pl-s">    }</span>
<span class="pl-s">    )<span class="pl-pds">"</span></span>;

    json val = json::parse(input);

    std::cout &lt;&lt; val &lt;&lt; std::endl;</pre></div>

<p>The output is</p>

<div class="highlight highlight-source-json"><pre>    {<span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>:<span class="pl-c1">10</span>,<span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Jane<span class="pl-pds">"</span></span>,<span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Roe<span class="pl-pds">"</span></span>}</pre></div>

<p>Note that on output, object members are sorted alphabetically by name.</p>

<h3>From a file</h3>

<p>The input file is</p>

<div class="highlight highlight-source-json"><pre>    {
        <span class="pl-ii">//</span> <span class="pl-ii">Members</span>
        <span class="pl-s"><span class="pl-pds">"</span>members<span class="pl-pds">"</span></span> : [
            {
                <span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Jane<span class="pl-pds">"</span></span>,
                <span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Roe<span class="pl-pds">"</span></span>,
                <span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>:<span class="pl-c1">10</span>,
                <span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span> : <span class="pl-c1">true</span>
            },
            {
                 <span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>John<span class="pl-pds">"</span></span>,
                 <span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Doe<span class="pl-pds">"</span></span>,
                 <span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>:<span class="pl-c1">2</span>,
                 <span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span> : <span class="pl-c1">true</span>
             }
        ]
    }</pre></div>

<p><code>members.json</code></p>

<div class="highlight highlight-source-c++"><pre>    json val = json::parse_file(<span class="pl-s"><span class="pl-pds">"</span>members.json<span class="pl-pds">"</span></span>);

    std::cout &lt;&lt; pretty_print(val) &lt;&lt; std::endl;</pre></div>

<p>The output is</p>

<div class="highlight highlight-source-json"><pre>    {
        <span class="pl-s"><span class="pl-pds">"</span>members<span class="pl-pds">"</span></span>:
        [
            {
                <span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span>:<span class="pl-c1">true</span>,
                <span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>:<span class="pl-c1">10</span>,
                <span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Jane<span class="pl-pds">"</span></span>,
                <span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Roe<span class="pl-pds">"</span></span>
            },
            {
                <span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span>:<span class="pl-c1">true</span>,
                <span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>:<span class="pl-c1">2</span>,
                <span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>John<span class="pl-pds">"</span></span>,
                <span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Doe<span class="pl-pds">"</span></span>
            }
        ]
    }</pre></div>

<p>Note that the parser accepts and ignores the single line comment that starts with the marker <code>//</code>.</p>

<h3>With code</h3>

<div class="highlight highlight-source-c++"><pre>    <span class="pl-c">// A boolean value</span>
    json <span class="pl-en">flag</span>(<span class="pl-c1">true</span>);

    <span class="pl-c">// A numeric value</span>
    json <span class="pl-en">number</span>(<span class="pl-c1">10.5</span>);

    <span class="pl-c">// An object value with four members</span>
    json obj;
    obj[<span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>] = <span class="pl-s"><span class="pl-pds">"</span>Jane<span class="pl-pds">"</span></span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>] = <span class="pl-s"><span class="pl-pds">"</span>Roe<span class="pl-pds">"</span></span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>] = <span class="pl-c1">10</span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span>] = <span class="pl-c1">true</span>;

    <span class="pl-c">// An array value with four elements</span>
    json arr = json::array();
    arr.add(json::null_type());
    arr.add(flag);
    arr.add(number);
    arr.add(obj);

    std::cout &lt;&lt; pretty_print(arr) &lt;&lt; std::endl;</pre></div>

<p>The output is</p>

<div class="highlight highlight-source-json"><pre>    [<span class="pl-c1">null</span>,<span class="pl-c1">true</span>,<span class="pl-c1">10.5</span>,
        {
            <span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span>:<span class="pl-c1">true</span>,
            <span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>:<span class="pl-c1">10</span>,
            <span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Jane<span class="pl-pds">"</span></span>,
            <span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>:<span class="pl-s"><span class="pl-pds">"</span>Roe<span class="pl-pds">"</span></span>
        }
    ]</pre></div>

<h3>From containers such as std::vector or std::list</h3>

<div class="highlight highlight-source-c++"><pre>    std::vector&lt;<span class="pl-k">int</span>&gt; vec;
    vec.push_back(<span class="pl-c1">10</span>);
    vec.push_back(<span class="pl-c1">20</span>);
    vec.push_back(<span class="pl-c1">30</span>);

    json <span class="pl-en">val1</span>(vec.begin(), vec.end());
    std::cout &lt;&lt; val1 &lt;&lt; std::endl;

    std::list&lt;<span class="pl-k">double</span>&gt; list;
    list.push_back(<span class="pl-c1">10.5</span>);
    list.push_back(<span class="pl-c1">20.5</span>);
    list.push_back(<span class="pl-c1">30.5</span>);

    json <span class="pl-en">val2</span>(list.begin(), list.end());
    std::cout &lt;&lt; val2 &lt;&lt; std::endl;</pre></div>

<p>The output is </p>

<div class="highlight highlight-source-json"><pre>    [<span class="pl-c1">10</span>,<span class="pl-c1">20</span>,<span class="pl-c1">30</span>]
    [<span class="pl-c1">10.5</span>,<span class="pl-c1">20.5</span>,<span class="pl-c1">30.5</span>]</pre></div>

<h2>Accessing object members and array elements</h2>

<h3>Accessing object members</h3>

<div class="highlight highlight-source-c++"><pre>    json obj;
    obj[<span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>] = <span class="pl-s"><span class="pl-pds">"</span>Jane<span class="pl-pds">"</span></span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>] = <span class="pl-s"><span class="pl-pds">"</span>Roe<span class="pl-pds">"</span></span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>] = <span class="pl-c1">10</span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span>] = <span class="pl-c1">true</span>;

    std::string first_name = obj[<span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>].as&lt;std::string&gt;();
    std::string last_name = obj.at(<span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>).as&lt;std::string&gt;();
    <span class="pl-k">int</span> events_attended = obj[<span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>].as&lt;<span class="pl-k">int</span>&gt;();
    <span class="pl-k">bool</span> accept_waiver_of_liability = obj[<span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span>].as&lt;<span class="pl-k">bool</span>&gt;();

    std::cout &lt;&lt; first_name &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span> <span class="pl-pds">"</span></span> &lt;&lt; last_name &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span>, <span class="pl-pds">"</span></span> &lt;&lt; events_attended 
              &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span>, <span class="pl-pds">"</span></span> &lt;&lt; accept_waiver_of_liability &lt;&lt; std::endl;</pre></div>

<p>The output is</p>

<pre><code>    Jane Roe, 10, 1
</code></pre>

<h3>Missing values and defaults</h3>

<div class="highlight highlight-source-c++"><pre>    json obj;
    obj[<span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>] = <span class="pl-s"><span class="pl-pds">"</span>Jane<span class="pl-pds">"</span></span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>] = <span class="pl-s"><span class="pl-pds">"</span>Roe<span class="pl-pds">"</span></span>;

    <span class="pl-k">try</span>
    {
        std::string experience = obj[<span class="pl-s"><span class="pl-pds">"</span>outdoor_experience<span class="pl-pds">"</span></span>].<span class="pl-smi">as</span>&lt;std::string&gt;();
    }
    <span class="pl-k">catch</span> (<span class="pl-k">const</span> json_exception&amp; e)
    {
        std::cout &lt;&lt; e.<span class="pl-c1">what</span>() &lt;&lt; std::endl;
    }

    std::string experience = obj.count(<span class="pl-s"><span class="pl-pds">"</span>outdoor_experience<span class="pl-pds">"</span></span>) &gt; <span class="pl-c1">0</span> ? obj[<span class="pl-s"><span class="pl-pds">"</span>outdoor_experience<span class="pl-pds">"</span></span>].as&lt;std::string&gt;() : <span class="pl-s"><span class="pl-pds">"</span><span class="pl-pds">"</span></span>;

    <span class="pl-k">bool</span> first_aid_certification = obj.get(<span class="pl-s"><span class="pl-pds">"</span>first_aid_certification<span class="pl-pds">"</span></span>,<span class="pl-c1">false</span>).as&lt;<span class="pl-k">bool</span>&gt;();

    std::cout &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span>experience=<span class="pl-pds">"</span></span> &lt;&lt; experience &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span>, first_aid_certification=<span class="pl-pds">"</span></span> &lt;&lt; first_aid_certification &lt;&lt; std::endl;</pre></div>

<p>The output is</p>

<pre><code>    Member outdoor_experience not found.
    experience=, first_aid_certification=0
</code></pre>

<h3>Iterating over the members of an object</h3>

<div class="highlight highlight-source-c++"><pre>    json obj;
    obj[<span class="pl-s"><span class="pl-pds">"</span>first_name<span class="pl-pds">"</span></span>] = <span class="pl-s"><span class="pl-pds">"</span>Jane<span class="pl-pds">"</span></span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>last_name<span class="pl-pds">"</span></span>] = <span class="pl-s"><span class="pl-pds">"</span>Roe<span class="pl-pds">"</span></span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>events_attended<span class="pl-pds">"</span></span>] = <span class="pl-c1">10</span>;
    obj[<span class="pl-s"><span class="pl-pds">"</span>accept_waiver_of_liability<span class="pl-pds">"</span></span>] = <span class="pl-c1">true</span>;

    <span class="pl-k">for</span> (<span class="pl-k">auto</span> it = obj.members().begin(); it != obj.members().end(); ++it)
    {
        std::cout &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span>name=<span class="pl-pds">"</span></span> &lt;&lt; it-&gt;<span class="pl-c1">name</span>() &lt;&lt; <span class="pl-s"><span class="pl-pds">"</span>, value=<span class="pl-pds">"</span></span> &lt;&lt; it-&gt;<span class="pl-c1">value</span>().<span class="pl-smi">as</span>&lt;std::string&gt;() &lt;&lt; std::endl;
    }</pre></div>

<p>The output is</p>

<pre><code>    name=accept_waiver_of_liability, value=true
    name=events_attended, value=10
    name=first_name, value=Jane
    name=last_name, value=Roe
</code></pre>

<h3>Iterating over the elements of an array</h3>

<div class="highlight highlight-source-c++"><pre>    json arr = json::array();
    arr.add(<span class="pl-s"><span class="pl-pds">"</span>Montreal<span class="pl-pds">"</span></span>);
    arr.add(<span class="pl-s"><span class="pl-pds">"</span>Toronto<span class="pl-pds">"</span></span>);
    arr.add(<span class="pl-s"><span class="pl-pds">"</span>Ottawa<span class="pl-pds">"</span></span>);
    arr.add(<span class="pl-s"><span class="pl-pds">"</span>Vancouver<span class="pl-pds">"</span></span>);

    <span class="pl-k">for</span> (<span class="pl-k">auto</span> it = arr.elements().begin(); it != arr.elements().end(); ++it)
    {
        std::cout &lt;&lt; it-&gt;as&lt;std::string&gt;() &lt;&lt; std::endl;
    }</pre></div>

<p>The output is</p>

<pre><code>    Montreal
    Toronto
    Ottawa
    Vancouver
</code></pre>
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