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| <h5 class="subsubsection">3.2.2.1 Basic Memory Allocation</h5> |
| |
| <p><a name="index-allocation-of-memory-with-_0040code_007bmalloc_007d-257"></a> |
| To allocate a block of memory, call <code>malloc</code>. The prototype for |
| this function is in <samp><span class="file">stdlib.h</span></samp>. |
| <a name="index-stdlib_002eh-258"></a> |
| <!-- malloc.h stdlib.h --> |
| <!-- ISO --> |
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| — Function: void * <b>malloc</b> (<var>size_t size</var>)<var><a name="index-malloc-259"></a></var><br> |
| <blockquote><p>This function returns a pointer to a newly allocated block <var>size</var> |
| bytes long, or a null pointer if the block could not be allocated. |
| </p></blockquote></div> |
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| <p>The contents of the block are undefined; you must initialize it yourself |
| (or use <code>calloc</code> instead; see <a href="Allocating-Cleared-Space.html#Allocating-Cleared-Space">Allocating Cleared Space</a>). |
| Normally you would cast the value as a pointer to the kind of object |
| that you want to store in the block. Here we show an example of doing |
| so, and of initializing the space with zeros using the library function |
| <code>memset</code> (see <a href="Copying-and-Concatenation.html#Copying-and-Concatenation">Copying and Concatenation</a>): |
| |
| <pre class="smallexample"> struct foo *ptr; |
| ... |
| ptr = (struct foo *) malloc (sizeof (struct foo)); |
| if (ptr == 0) abort (); |
| memset (ptr, 0, sizeof (struct foo)); |
| </pre> |
| <p>You can store the result of <code>malloc</code> into any pointer variable |
| without a cast, because ISO C<!-- /@w --> automatically converts the type |
| <code>void *</code> to another type of pointer when necessary. But the cast |
| is necessary in contexts other than assignment operators or if you might |
| want your code to run in traditional C. |
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| <p>Remember that when allocating space for a string, the argument to |
| <code>malloc</code> must be one plus the length of the string. This is |
| because a string is terminated with a null character that doesn't count |
| in the “length” of the string but does need space. For example: |
| |
| <pre class="smallexample"> char *ptr; |
| ... |
| ptr = (char *) malloc (length + 1); |
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| <p class="noindent">See <a href="Representation-of-Strings.html#Representation-of-Strings">Representation of Strings</a>, for more information about this. |
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