devdocs/c/memory%2Fmalloc.html


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    <h1 id="firstHeading" class="firstHeading">malloc</h1>            <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code>&lt;stdlib.h&gt;</code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl"> <td class="t-dcl-nopad"> <pre data-language="c">void *malloc( size_t size );</pre>
</td> <td class="t-dcl-nopad"> </td> <td class="t-dcl-nopad"> </td> </tr>  </table> <p>Allocates <code>size</code> bytes of uninitialized storage.</p>
<p>If allocation succeeds, returns a pointer that is suitably aligned for any object type with <a href="../language/object#Alignment" title="c/language/object">fundamental alignment</a>.</p>
<p>If <code>size</code> is zero, the behavior of <code>malloc</code> is implementation-defined. For example, a null pointer may be returned. Alternatively, a non-null pointer may be returned; but such a pointer should not be <a href="../language/operator_member_access" title="c/language/operator member access">dereferenced</a>, and should be passed to <code><a href="free" title="c/memory/free">free</a></code> to avoid memory leaks.</p>
<table class="t-rev-begin"> <tr class="t-rev t-since-c11">
<td> <p><code>malloc</code> is thread-safe: it behaves as though only accessing the memory locations visible through its argument, and not any static storage.</p>
<p>A previous call to <code><a href="free" title="c/memory/free">free</a></code> or <code><a href="realloc" title="c/memory/realloc">realloc</a></code> that deallocates a region of memory <i>synchronizes-with</i> a call to <code>malloc</code> that allocates the same or a part of the same region of memory. This synchronization occurs after any access to the memory by the deallocating function and before any access to the memory by <code>malloc</code>. There is a single total order of all allocation and deallocation functions operating on each particular region of memory.</p>
</td> <td><span class="t-mark-rev t-since-c11">(since C11)</span></td>
</tr> </table>  <h3 id="Parameters"> Parameters</h3> <table class="t-par-begin"> <tr class="t-par"> <td> size </td> <td> - </td> <td> number of bytes to allocate </td>
</tr>
</table> <h3 id="Return_value"> Return value</h3> <p>On success, returns the pointer to the beginning of newly allocated memory. To avoid a memory leak, the returned pointer must be deallocated with <code><a href="free" title="c/memory/free">free()</a></code> or <code><a href="realloc" title="c/memory/realloc">realloc()</a></code>.</p>
<p>On failure, returns a null pointer.</p>
<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include &lt;stdio.h&gt;   
#include &lt;stdlib.h&gt; 
 
int main(void) 
{
    int *p1 = malloc(4*sizeof(int));  // allocates enough for an array of 4 int
    int *p2 = malloc(sizeof(int[4])); // same, naming the type directly
    int *p3 = malloc(4*sizeof *p3);   // same, without repeating the type name
 
    if(p1) {
        for(int n=0; n&lt;4; ++n) // populate the array
            p1[n] = n*n;
        for(int n=0; n&lt;4; ++n) // print it back out
            printf("p1[%d] == %d\n", n, p1[n]);
    }
 
    free(p1);
    free(p2);
    free(p3);
}</pre></div> <p>Output:</p>
<div class="text source-text"><pre data-language="c">p1[0] == 0
p1[1] == 1
p1[2] == 4
p1[3] == 9</pre></div> </div> <h3 id="References"> References</h3>  <ul>
<li> C17 standard (ISO/IEC 9899:2018): </li>
<ul><li> 7.22.3.4 The malloc function (p: 254) </li></ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul><li> 7.22.3.4 The malloc function (p: 349) </li></ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul><li> 7.20.3.3 The malloc function (p: 314) </li></ul>
<li> C89/C90 standard (ISO/IEC 9899:1990): </li>
<ul><li> 4.10.3.3 The malloc function </li></ul>
</ul>               <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="free" title="c/memory/free"> <span class="t-lines"><span>free</span></span></a></div> </td> <td> deallocates previously allocated memory <br> <span class="t-mark">(function)</span>  </td>
</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/memory/c/malloc" title="cpp/memory/c/malloc">C++ documentation</a></span> for <code>malloc</code> </td>
</tr> </table>           <div class="_attribution">
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