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c:stdlib.h:malloc

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c:stdlib.h:malloc [2013/01/22 22:02] (current)
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 +{{keywords>wiki library source code example reference}}
 +====== malloc ======
 +<code c>
 +    #include <stdlib.h>
 +    void *malloc(size_t size);
 +</code>
 +
 +=== description ===
 +The malloc() function shall allocate unused space for an object whose size in bytes is specified by size and whose value is unspecified.\\
 +\\
 +The order and contiguity of storage allocated by successive calls to malloc() is unspecified.\\
 +The pointer returned if the allocation succeeds shall be suitably aligned so that it may be assigned to a pointer \\
 +to any type of object and then used to access such an object in the space allocated (until the space is explicitly freed or reallocated). \\
 +Each such allocation shall yield a pointer to an object disjoint from any other object. The pointer returned points\\
 +to the start (lowest byte address) of the allocated space. If the space cannot be allocated, a null pointer shall be returned.\\
 +If the size of the space requested is 0, the behavior is implementation-defined: the value returned shall be either a null pointer or a unique pointer.\\
 +
 +
 +=== return value ===
 +RETURN VALUE
 +
 +Upon successful completion with size not equal to 0, malloc() shall return a pointer to the allocated space.\\
 +If size is 0, either a null pointer or a unique pointer that can be successfully passed to free() shall be returned.\\
 +Otherwise, it shall return a null pointer and set errno to indicate the error. \\
 +
 +===== malloc c code example =====  
 +<code c>
 +/* 
 + * malloc example code
 + * http://code-reference.com/c/stdlib.h/malloc
 + */
 +#include <stdio.h> /* including standard library */
 +//#include <windows.h> /* uncomment this for Windows */
 + 
 +#include <stdlib.h>
 + 
 +int testit ( int *x )
 +{
 +     if (x != NULL) {
 +         printf("allocation of memory was successfully.\n");
 +     }
 +     else {
 +          printf("allocation of memory failed.\n");
 +     }
 +return 0;
 +}
 +
 +int main ( void )
 +{
 +  int *buffer, i;
 +
 +  printf("how many int to malloc ?: ");
 +  scanf("%i", &i);
 +  
 +  printf("set buffer to %i * %i = %d bytes\n",i, sizeof(int), i*sizeof(int));
 +
 +  buffer = (int*) malloc (i*sizeof(int)); // i * size of int... eg. 100 * 4byte
 +  testit(buffer); 
 + 
 +  printf("try to free the buffer\n");
 +  free (buffer);
 +  return 0;
 +}
 +</code>
 +
 +==== Output ====
 +
 +    Output allocation successfully:
 +    user@host:~$  ./malloc 
 +    how many int to malloc ?: 999999
 +    set buffer to 999999 * 4 = 3999996 bytes
 +    allocation of memory was successfully.
 +    try to free the buffer
 +
 +
 +    Output allocation failed:
 +    user@host:~$  .//malloc 
 +    how many int to malloc ?: 1234567890123
 +    set buffer to 2147483647 * 4 = -4 bytes
 +    allocation of memory failed.
 +    try to free the buffer
 +
 +
  
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c/stdlib.h/malloc.txt · Last modified: 2013/01/22 22:02 (external edit)

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