devdocs/c/types%2Fnullptr_t.html


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    <h1 id="firstHeading" class="firstHeading">nullptr_t</h1>            <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code>&lt;stddef.h&gt;</code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c23"> <td> <pre data-language="c">typedef typeof(nullptr) nullptr_t;</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c23">(since C23)</span> </td> </tr>  </table> <p><code>nullptr_t</code> is the type of the predefined null pointer constant, <a href="../language/nullptr" title="c/language/nullptr"><code>nullptr</code></a>. It is a distinct type that is not itself a pointer type. It can be <a href="../language/conversion" title="c/language/conversion">implicitly converted</a> to any pointer type or <code>bool</code>, and the result is the null pointer value of that type or <code>false</code> respectively. No type other than <code>nullptr_t</code> itself can be converted or explicitly cast to <code>nullptr_t</code>.</p>
<p><code>sizeof(nullptr_t)</code> and <code>alignof(nullptr_t)</code> are equal to <code>sizeof(void*)</code> and <code>alignof(void*)</code> respectively.</p>
<p><code>nullptr_t</code> has only one valid value, i.e., <code>nullptr</code>. The object representation of <code>nullptr</code> is same as that of <code>(void*)0</code>. If a program produces a <code>nullptr_t</code> value with a different object representation, the behavior is undefined.</p>
<h3 id="Example"> Example</h3> <div class="t-example">
<p>Demonstrate that <code>nullptr_t</code> is a distinct type.</p>
<div class="c source-c"><pre data-language="c">#include &lt;stddef.h&gt;
#include &lt;stdio.h&gt;
 
#define DETECT_NULL_POINTER_CONSTANT(e) \
    _Generic(e,                         \
        void* : puts("void*"),          \
        nullptr_t : puts("nullptr_t"),  \
        default : puts("other")       \
    )
 
int main()
{
    DETECT_NULL_POINTER_CONSTANT(((void*)0));
    DETECT_NULL_POINTER_CONSTANT(0);
    DETECT_NULL_POINTER_CONSTANT(nullptr);
}</pre></div> <p>Output:</p>
<div class="text source-text"><pre data-language="c">void*
other
nullptr_t</pre></div> </div> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="null" title="c/types/NULL"> <span class="t-lines"><span>NULL</span></span></a></div> </td> <td> implementation-defined null pointer constant <br> <span class="t-mark">(macro constant)</span>  </td>
</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/types/nullptr_t" title="cpp/types/nullptr t">C++ documentation</a></span> for <code>nullptr_t</code> </td>
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