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<h1 id="firstHeading" class="firstHeading">Type support</h1> <p>See also <a href="language/types" title="c/language/types" class="mw-redirect"> type system overview</a> and <a href="language/arithmetic_types" title="c/language/arithmetic types"> arithmetic types defined by the language</a>.</p>
<h3 id="Basic_types"> Basic types</h3> <h4 id="Additional_basic_types_and_convenience_macros"> Additional basic types and convenience macros</h4> <table class="t-dsc-begin"> <tr class="t-dsc-header"> <th colspan="2"> Defined in header <code><stddef.h></code> </th>
</tr> <tr class="t-dsc"> <td> <div><a href="types/size_t" title="c/types/size t"> <span class="t-lines"><span>size_t</span></span></a></div> </td> <td> unsigned integer type returned by the <a href="language/sizeof" title="c/language/sizeof"><code>sizeof</code></a> operator <br> <span class="t-mark">(typedef)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="types/ptrdiff_t" title="c/types/ptrdiff t"> <span class="t-lines"><span>ptrdiff_t</span></span></a></div> </td> <td> signed integer type returned when subtracting two pointers <br> <span class="t-mark">(typedef)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="types/nullptr_t" title="c/types/nullptr t"> <span class="t-lines"><span>nullptr_t</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c23">(C23)</span></span></span></div> </td> <td> the type of the predefined null pointer constant <a href="language/nullptr" title="c/language/nullptr"><code>nullptr</code></a> <br> <span class="t-mark">(typedef)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="types/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> <div><a href="types/max_align_t" title="c/types/max align t"> <span class="t-lines"><span>max_align_t</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div> </td> <td> a type with alignment requirement as great as any other scalar type <br> <span class="t-mark">(typedef)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><a href="types/offsetof" title="c/types/offsetof"> <span class="t-lines"><span>offsetof</span></span></a></div> </td> <td> byte offset from the beginning of a struct type to specified member <br> <span class="t-mark">(function macro)</span> </td>
</tr> <tr class="t-dsc-header"> <th colspan="2"> Defined in header <code><stdbool.h></code> </th>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>bool</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span><span class="t-mark-rev t-until-c23">(removed in C23)</span></span></span></div> </td> <td> convenience macro, expands to <a href="keyword/_bool" title="c/keyword/ Bool"><code>_Bool</code></a> <br> <span class="t-mark">(keyword macro)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>true</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span><span class="t-mark-rev t-until-c23">(removed in C23)</span></span></span></div> </td> <td> expands to integer constant <code>1</code> <br> <span class="t-mark">(macro constant)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>false</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span><span class="t-mark-rev t-until-c23">(removed in C23)</span></span></span></div> </td> <td> expands to integer constant <code>0</code> <br> <span class="t-mark">(macro constant)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>__bool_true_false_are_defined</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span><span class="t-mark-rev t-deprecated-c23">(deprecated in C23)</span></span></span></div> </td> <td> expands to integer constant <code>1</code> <br> <span class="t-mark">(macro constant)</span> </td>
</tr> <tr class="t-dsc-header"> <th colspan="2"> Defined in header <code><stdalign.h></code> </th>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>alignas</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span><span class="t-mark-rev t-until-c23">(removed in C23)</span></span></span></div> </td> <td> convenience macro, expands to keyword <a href="keyword/_alignas" title="c/keyword/ Alignas"><code>_Alignas</code></a> <br> <span class="t-mark">(keyword macro)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>alignof</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span><span class="t-mark-rev t-until-c23">(removed in C23)</span></span></span></div> </td> <td> convenience macro, expands to keyword <a href="keyword/_alignof" title="c/keyword/ Alignof"><code>_Alignof</code></a> <br> <span class="t-mark">(keyword macro)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>__alignas_is_defined</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span><span class="t-mark-rev t-until-c23">(removed in C23)</span></span></span></div> </td> <td> expands to integer constant <code>1</code> <br> <span class="t-mark">(macro constant)</span> </td>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>__alignof_is_defined</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span><span class="t-mark-rev t-until-c23">(removed in C23)</span></span></span></div> </td> <td> expands to integer constant <code>1</code> <br> <span class="t-mark">(macro constant)</span> </td>
</tr> <tr class="t-dsc-header"> <th colspan="2"> Defined in header <code><stdnoreturn.h></code> </th>
</tr> <tr class="t-dsc"> <td> <div><span class="t-lines"><span>noreturn</span></span></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c11">(C11)</span><span class="t-mark-rev t-deprecated-c23">(deprecated in C23)</span></span></span></div> </td> <td> convenience macro, expands to <a href="keyword/_noreturn" title="c/keyword/ Noreturn"><code>_Noreturn</code></a> <br> <span class="t-mark">(keyword macro)</span> </td>
</tr> </table> <h4 id="Fixed_width_integer_types_.28since_C99.29"> <a href="types/integer" title="c/types/integer"> Fixed width integer types</a> <span class="t-mark-rev t-since-c99">(since C99)</span>
</h4> <h4 id="Numeric_limits"> <a href="types/limits" title="c/types/limits"> Numeric limits</a>
</h4> <h3 id="Notes"> Notes</h3> <table class="t-rev-begin"> <tr class="t-rev t-since-c99 t-until-c23">
<td> <p>The type of <code>true</code> and <code>false</code> is <code>int</code> rather than <code>_Bool</code>.</p>
<p>A program may undefine and perhaps then redefine the macros <code>bool</code>, <code>true</code> and <code>false</code>. However, such ability is a deprecated feature.</p>
</td> <td>
<span class="t-mark-rev t-since-c99">(since C99)</span><br><span class="t-mark-rev t-until-c23">(until C23)</span>
</td>
</tr> <tr class="t-rev t-since-c23">
<td> <p>The type of <code>true</code> and <code>false</code> is <code>bool</code>. It is unspecified whether any of <code>bool</code>, <code>_Bool</code>, <code>true</code>, or <code>false</code> is implemented as a predefined macro.</p>
<p>If <code>bool</code>, <code>true</code>, or <code>false</code> (but not <code>_Bool</code>) is defined as a predefined macro, a program may undefine and perhaps redefine it.</p>
</td> <td><span class="t-mark-rev t-since-c23">(since C23)</span></td>
</tr> </table> <h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include <stdio.h>
#include <stdbool.h>
#include <stdalign.h>
int main(void)
{
printf("%d %d %d\n", true && false, true || false, !false);
printf("%d %d\n", true ^ true, true + true);
printf("%zu\n", alignof(short));
}</pre></div> <p>Possible output:</p>
<div class="text source-text"><pre data-language="c">0 1 1
0 2
2</pre></div> </div> <h3 id="References"> References</h3> <ul>
<li> C17 standard (ISO/IEC 9899:2018): </li>
<ul>
<li> 7.15 Alignment <stdalign.h> (p: 196) </li>
<li> 7.18 Boolean type and values <stdbool.h> (p: 210) </li>
<li> 7.19 Common definitions <stddef.h> (p: 211) </li>
<li> 7.23 _Noreturn <stdnoreturn.h> (p: 263) </li>
<li> 7.31.9 Boolean type and values <stdbool.h> (p: 332) </li>
</ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul>
<li> 7.15 Alignment <stdalign.h> (p: 268) </li>
<li> 7.18 Boolean type and values <stdbool.h> (p: 287) </li>
<li> 7.19 Common definitions <stddef.h> (p: 288) </li>
<li> 7.23 _Noreturn <stdnoreturn.h> (p: 361) </li>
<li> 7.31.9 Boolean type and values <stdbool.h> (p: 456) </li>
</ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul>
<li> 7.18 Boolean type and values <stdbool.h> (p: 253) </li>
<li> 7.19 Common definitions <stddef.h> (p: 254) </li>
<li> 7.26.7 Boolean type and values <stdbool.h> (p: 401) </li>
</ul>
<li> C89/C90 standard (ISO/IEC 9899:1990): </li>
<ul><li> 4.1.5 Common definitions <stddef.h> </li></ul>
</ul> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/types" title="cpp/types">C++ documentation</a></span> for <span class=""><span>Type support library</span></span> </td>
</tr> </table> <div class="_attribution">
<p class="_attribution-p">
© cppreference.com<br>Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.<br>
<a href="https://en.cppreference.com/w/c/types" class="_attribution-link">https://en.cppreference.com/w/c/types</a>
</p>
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