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malloc(3) [netbsd man page]

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 coer- cion) 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 identically 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 ear- lier, a return value of NULL indicates that the old object still remains allocated. 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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mapmalloc(3MALLOC)					Memory Allocation Library Functions					mapmalloc(3MALLOC)

NAME
mapmalloc - memory allocator SYNOPSIS
cc [ flag ... ] file ... -lmapmalloc [ library ... ] #include <stdlib.h> void *malloc(size_t size); void *calloc(size_t nelem, size_t elsize); void free(void * ptr); void *realloc(void *ptr, size_t size); DESCRIPTION
The collection of malloc functions in this library use mmap(2) instead of sbrk(2) for acquiring new heap space. The functions in this library are intended to be used only if necessary, when applications must call sbrk(), but need to call other library routines that might call malloc. The algorithms used by these functions are not sophisticated. There is no reclaiming of memory. The malloc() and free() functions provide a simple general-purpose memory allocation package. The malloc() function returns a pointer to a block of at least size bytes suitably aligned for any use. The argument to free() is a pointer to a block previously allocated by malloc(), calloc() or realloc(). If ptr is a NULL pointer, no action occurs. Undefined results will occur if the space assigned by malloc() is overrun or if some random number is handed to free(). The calloc() function allocates space for an array of nelem elements of size elsize. The space is initialized to zeros. The realloc() function changes the size of the block pointed to by ptr to size bytes and returns a pointer to the (possibly moved) block. The contents will be unchanged up to the lesser of the new and old sizes. If the new size of the block requires movement of the block, the space for the previous instantiation of the block is freed. If the new size is larger, the contents of the newly allocated portion of the block are unspecified. If ptr is NULL, realloc() behaves like malloc() for the specified size. If size is 0 and ptr is not a null pointer, the space pointed to is freed. Each of the allocation functions returns a pointer to space suitably aligned (after possible pointer coercion) for storage of any type of object. The malloc() and realloc() functions will fail if there is not enough available memory. Entry points for malloc_debug(), mallocmap(), mallopt(), mallinfo(), memalign(), and valloc() are empty routines, and are provided only to protect the user from mixing malloc() functions from different implementations. RETURN VALUES
If there is no available memory, malloc(), realloc(), and calloc() return a null pointer. When realloc() returns NULL, the block pointed to by ptr is left intact. If size, nelem, or elsize is 0, a unique pointer to the arena is returned. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |MT-Level |Safe | +-----------------------------+-----------------------------+ SEE ALSO
brk(2), getrlimit(2), mmap(2), realloc(3C), malloc(3MALLOC), attributes(5) SunOS 5.11 20 Feb 2004 mapmalloc(3MALLOC)
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