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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="initialization.html#Explicit_initialization" title="c/language/initialization"><span class="t-lines"><span>explicit initialization</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="initialization.html#Implicit_initialization" title="c/language/initialization"><span class="t-lines"><span>implicit initialization</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="scalar_initialization.html" title="c/language/scalar initialization"><span class="t-lines"><span>scalar initialization</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="array_initialization.html" title="c/language/array initialization"><span class="t-lines"><span>array initialization</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="struct_initialization.html" title="c/language/struct initialization"><span class="t-lines"><span>struct and union initialization</span></span></a></div></div></td></tr>
</table></div>
</div><div><span class="editsection noprint plainlinks" title="Edit this template"><a rel="nofollow" class="external text" href="http://en.cppreference.com/mwiki/index.php?title=Template:c/language/initialization/navbar_content&action=edit">[edit]</a></span></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>A <a href="declarations.html" title="c/language/declarations">declaration</a> of an object may provide its initial value through the process known as <i>initialization</i>.
</p><p>For each <a href="declarations.html" title="c/language/declarations">declarator</a>, the initializer, if not omitted, may be one of the following:
</p>
<table class="t-sdsc-begin">
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>=</b></code> <span class="t-spar">expression</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>=</b></code> <code><b>{ </b></code> <span class="t-spar">initializer-list</span> <code><b>} </b></code>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>where <span class="t-spar">initializer-list</span> is a non-empty comma-separated list of <span class="t-spar">initializer</span>s (with an optional trailing comma), where each initializer has one of three possible forms:
</p>
<table class="t-sdsc-begin">
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">expression</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>{ </b></code> <span class="t-spar">initializer-list</span> <code><b>} </b></code>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">designator-list</span> <code><b>=</b></code> <span class="t-spar">initializer</span>
</td>
<td> (3)
</td>
<td class="t-sdsc-nopad">
</td></tr>
<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>where <span class="t-spar">designator-list</span> is a list of either array designators of the form <code><b>[</b></code> <span class="t-spar">constant-expression</span> <code><b>]</b></code> or struct/union member designators of the form <code><b>.</b></code> <span class="t-spar">identifier</span>; see
<a href="array_initialization.html" title="c/language/array initialization">array initialization</a> and <a href="struct_initialization.html" title="c/language/struct initialization">struct initialization</a>.
</p>
<table id="toc" class="toc"><tr><td><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="initialization.html#Explanation"><span class="tocnumber">1</span> <span class="toctext">Explanation</span></a>
<ul>
<li class="toclevel-2 tocsection-2"><a href="initialization.html#Explicit_initialization"><span class="tocnumber">1.1</span> <span class="toctext">Explicit initialization</span></a></li>
<li class="toclevel-2 tocsection-3"><a href="initialization.html#Implicit_initialization"><span class="tocnumber">1.2</span> <span class="toctext">Implicit initialization</span></a></li>
</ul>
</li>
<li class="toclevel-1 tocsection-4"><a href="initialization.html#Notes"><span class="tocnumber">2</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="initialization.html#Example"><span class="tocnumber">3</span> <span class="toctext">Example</span></a></li>
<li class="toclevel-1 tocsection-6"><a href="initialization.html#References"><span class="tocnumber">4</span> <span class="toctext">References</span></a></li>
<li class="toclevel-1 tocsection-7"><a href="initialization.html#See_also"><span class="tocnumber">5</span> <span class="toctext">See also</span></a></li>
</ul>
</td></tr></table>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/initialization&action=edit&section=1" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span></h3>
<p>The initializer specifies the initial value stored in an object.
</p>
<h4><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/initialization&action=edit&section=2" title="Edit section: Explicit initialization">edit</a>]</span> <span class="mw-headline" id="Explicit_initialization">Explicit initialization</span></h4>
<p>If an initializer is provided, see
</p>
<ul><li> <a href="scalar_initialization.html" title="c/language/scalar initialization">scalar initialization</a> for the initialization of scalar types
</li><li> <a href="array_initialization.html" title="c/language/array initialization">array initialization</a> for the initialization of array types
</li><li> <a href="struct_initialization.html" title="c/language/struct initialization">struct initialization</a> for the initialization of struct and union types.
</li></ul>
<h4><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/initialization&action=edit&section=3" title="Edit section: Implicit initialization">edit</a>]</span> <span class="mw-headline" id="Implicit_initialization">Implicit initialization</span></h4>
<p>If an initializer is not provided:
</p>
<ul><li> objects with automatic <a href="storage_duration.html" title="c/language/storage duration">storage duration</a> are initialized to indeterminate values (which may be <a href="object.html" title="c/language/object">trap representations</a>)
</li><li> objects with static and thread-local <a href="storage_duration.html" title="c/language/storage duration">storage duration</a> are initialized as follows
</li></ul>
<dl><dd><ul><li> pointers are initialized to null pointer values of their types
</li><li> objects of integral types are initialized to unsigned zero
</li><li> objects of floating types are initialized to positive zero
</li><li> members of arrays, structs, and unions are initialized as described above, recursively, plus all padding bits are initialized to zero
</li></ul>
</dd><dd>(on platforms where null pointers and floating zeroes have all-bit-zero representations, this form of initialization for statics is normally implemented by allocating them in the .bss section of the program image)
</dd></dl>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/initialization&action=edit&section=4" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span></h3>
<p>When initializing an object of static or thread-local <a href="storage_duration.html" title="c/language/storage duration">storage duration</a>, every <span class="t-spar">expression</span> in the initializer must be a <a href="constant_expression.html" title="c/language/constant expression">constant expression</a> or <a href="string_literal.html" title="c/language/string literal">string literal</a>.
</p><p>Initializers cannot be used in declarations of objects of incomplete type, VLAs, and block-scope objects with linkage.
</p><p>The initial values of function parameters are established as if by assignment from the arguments of a <a href="operator_other.html#Function_call" title="c/language/operator other">function call</a>, rather than by initialization (until the post-C11 defect report DR 427, which changes the wording to use initialization).
</p><p>If an indeterminate value is used as an argument to any standard library call, the behavior is undefined. Otherwise, the result of any expression involving indeterminate values is an indeterminate value (e.g. int n; may not compare equal to itself and it may appear to change its value on subsequent reads)
</p>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/initialization&action=edit&section=5" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include <stdlib.h></span>
<span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// initializes a to {0, 0}</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="kw4">int</span> i<span class="sy4">;</span> <span class="co1">// initializes i to an indeterminate value</span>
<span class="kw4">static</span> <span class="kw4">int</span> j<span class="sy4">;</span> <span class="co1">// initializes j to 0</span>
<span class="kw4">int</span> k <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> <span class="co1">// initializes k to 1</span>
 
<span class="co1">// initializes int x[3] to 1,3,5</span>
<span class="co1">// initializes int* p to &x[0]</span>
<span class="kw4">int</span> x<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="nu0">1</span>, <span class="nu0">3</span>, <span class="nu0">5</span> <span class="br0">}</span>, <span class="sy2">*</span>p <span class="sy1">=</span> x<span class="sy4">;</span>
 
<span class="co1">// initializes w (an array of two structs) to</span>
<span class="co1">// { { {1,0,0}, 0}, { {2,0,0}, 0} }</span>
<span class="kw1">struct</span> <span class="br0">{</span><span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span>, b<span class="sy4">;</span><span class="br0">}</span> w<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>.<span class="me1">a</span> <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span><span class="br0">}</span>, <span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span>.<span class="me1">a</span><span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">2</span><span class="br0">}</span><span class="sy4">;</span>
 
<span class="co1">// function call expression can be used for a local variable</span>
<span class="kw4">char</span><span class="sy2">*</span> ptr <span class="sy1">=</span> <a href="../memory/malloc.html"><span class="kw403">malloc</span></a><span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span>
<a href="../memory/free.html"><span class="kw406">free</span></a><span class="br0">(</span>ptr<span class="br0">)</span><span class="sy4">;</span>
 
<span class="co1">// Error: objects with static storage duration require constant initializers</span>
<span class="co1">// static char* ptr = malloc(10);</span>
 
<span class="co1">// Error: VLA cannot be initialized</span>
<span class="co1">// int vla[n] = {0};</span>
<span class="br0">}</span></pre></div></div>
<p><br />
</p>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/initialization&action=edit&section=6" title="Edit section: References">edit</a>]</span> <span class="mw-headline" id="References">References</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011):
</li></ul>
<dl><dd><ul><li> 6.7.9 Initialization (p: 139-144)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999):
</li></ul>
<dl><dd><ul><li> 6.7.8 Initialization (p: 125-130)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990):
</li></ul>
<dl><dd><ul><li> 3.5.7 Initialization
</li></ul>
</dd></dl>
</div>
<h3><span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php?title=c/language/initialization&action=edit&section=7" title="Edit section: See also">edit</a>]</span> <span class="mw-headline" id="See_also">See also</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td colspan="2"> <div class="t-dsc-see"><span><a href="../../cpp/language/initialization.html" title="cpp/language/initialization">C++ documentation</a></span> for <span class="t-dsc-see-tt"><span>Initialization</span></span></div>
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