MAPMALLOC(3MALLOC) Memory Allocation Library Functions MAPMALLOC(3MALLOC)


mapmalloc - memory allocator


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);


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

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

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


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.


See attributes(7) for descriptions of the following attributes:

|MT-Level | Safe |


brk(2), getrlimit(2), mmap(2), realloc(3C), malloc(3MALLOC),

illumos February 20, 2004 MAPMALLOC(3MALLOC)