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| <h4 class="subsection">3.2.5 Automatic Storage with Variable Size</h4> |
| |
| <p><a name="index-automatic-freeing-341"></a><a name="index-g_t_0040code_007balloca_007d-function-342"></a><a name="index-automatic-storage-with-variable-size-343"></a> |
| The function <code>alloca</code> supports a kind of half-dynamic allocation in |
| which blocks are allocated dynamically but freed automatically. |
| |
| <p>Allocating a block with <code>alloca</code> is an explicit action; you can |
| allocate as many blocks as you wish, and compute the size at run time. But |
| all the blocks are freed when you exit the function that <code>alloca</code> was |
| called from, just as if they were automatic variables declared in that |
| function. There is no way to free the space explicitly. |
| |
| <p>The prototype for <code>alloca</code> is in <samp><span class="file">stdlib.h</span></samp>. This function is |
| a BSD extension. |
| <a name="index-stdlib_002eh-344"></a> |
| <!-- stdlib.h --> |
| <!-- GNU, BSD --> |
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| <div class="defun"> |
| — Function: void * <b>alloca</b> (<var>size_t size</var>)<var>;<a name="index-alloca-345"></a></var><br> |
| <blockquote><p>The return value of <code>alloca</code> is the address of a block of <var>size</var> |
| bytes of memory, allocated in the stack frame of the calling function. |
| </p></blockquote></div> |
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| <p>Do not use <code>alloca</code> inside the arguments of a function call—you |
| will get unpredictable results, because the stack space for the |
| <code>alloca</code> would appear on the stack in the middle of the space for |
| the function arguments. An example of what to avoid is <code>foo (x, |
| alloca (4), y)</code>. |
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| method of allocating dynamically and |
| freeing automatically. |
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