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NetBSD 6.1.5 - man page for realloc (netbsd section 3)

MALLOC(3)			   BSD Library Functions Manual 			MALLOC(3)

NAME
     malloc, calloc, realloc, free -- general purpose memory allocation functions

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdlib.h>

     void *
     malloc(size_t size);

     void *
     calloc(size_t number, size_t size);

     void *
     realloc(void *ptr, size_t size);

     void
     free(void *ptr);

DESCRIPTION
     The malloc() function allocates size bytes of uninitialized memory.  The allocated space is
     suitably aligned (after possible pointer coercion) for storage of any type of object.

     The calloc() function allocates space for number objects, each size bytes in length.  The
     result is identical to calling malloc() with an argument of ``number * size'', with the
     exception that the allocated memory is explicitly initialized to zero bytes.

     The realloc() function changes the size of the previously allocated memory referenced by ptr
     to size bytes.  The contents of the memory are unchanged up to the lesser of the new and old
     sizes.  If the new size is larger, the value of the newly allocated portion of the memory is
     undefined.  Upon success, the memory referenced by ptr is freed and a pointer to the newly
     allocated memory is returned.  Note that realloc() may move the memory allocation, resulting
     in a different return value than ptr.  If ptr is NULL, the realloc() function behaves iden-
     tically to malloc() for the specified size.

     The free() function causes the allocated memory referenced by ptr to be made available for
     future allocations.  If ptr is NULL, no action occurs.

RETURN VALUES
     The malloc() and calloc() functions return a pointer to the allocated memory if successful;
     otherwise a NULL pointer is returned and errno is set to ENOMEM.

     The realloc() function returns a pointer, possibly identical to ptr, to the allocated memory
     if successful; otherwise a NULL pointer is returned, and errno is set to ENOMEM if the error
     was the result of an allocation failure.  The realloc() function always leaves the original
     buffer intact when an error occurs.

     The free() function returns no value.

EXAMPLES
     When using malloc(), be careful to avoid the following idiom:

	   if ((p = malloc(number * size)) == NULL)
		   err(EXIT_FAILURE, "malloc");

     The multiplication may lead to an integer overflow.  To avoid this, calloc() is recommended.

     If malloc() must be used, be sure to test for overflow:

	   if (size && number > SIZE_MAX / size) {
		   errno = EOVERFLOW;
		   err(EXIT_FAILURE, "allocation");
	   }

     When using realloc(), one must be careful to avoid the following idiom:

	   nsize += 50;

	   if ((p = realloc(p, nsize)) == NULL)
		   return NULL;

     Do not adjust the variable describing how much memory has been allocated until it is known
     that the allocation has been successful.  This can cause aberrant program behavior if the
     incorrect size value is used.  In most cases, the above example will also leak memory.  As
     stated earlier, a return value of NULL indicates that the old object still remains allo-
     cated.  Better code looks like this:

	   newsize = size + 50;

	   if ((p2 = realloc(p, newsize)) == NULL) {

		   if (p != NULL)
			   free(p);

		   p = NULL;
		   return NULL;
	   }

	   p = p2;
	   size = newsize;

SEE ALSO
     madvise(2), mmap(2), sbrk(2), alloca(3), atexit(3), getpagesize(3), memory(3),
     posix_memalign(3)

     For the implementation details, see jemalloc(3).

STANDARDS
     The malloc(), calloc(), realloc() and free() functions conform to ISO/IEC 9899:1990
     (``ISO C90'').

BSD					   May 3, 2010					      BSD


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