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MALLOC(3C)							    MALLOC(3C)

NAME    [Toc]    [Back]

     malloc, free, realloc, calloc, memalign, valloc - main memory allocator

SYNOPSIS    [Toc]    [Back]

     #include <stdlib.h>

     void *malloc (size_t size);

     void free (void *ptr);

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

     void *calloc (size_t nelem, size_t	elsize);

     void *memalign (size_t alignment, size_t size);

     void *valloc (size_t size);

DESCRIPTION    [Toc]    [Back]

     malloc and	free provide a simple general-purpose memory allocation
     package.  malloc 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; after free	is performed this space	is made	available for further
     allocation, but its contents are left undisturbed.

     Undefined results will occur if the space allocated by malloc is overrun
     or	if some	random value is	passed as the argument to free.

     malloc allocates the first	big enough contiguous reach of free space
     found in a	circular search	from the last block allocated or freed,
     coalescing	adjacent free blocks as	it searches.  It calls sbrk [see
     brk(2)] to	get more memory	from the system	when there is no suitable
     space already free.

     realloc 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 no free block of
     size bytes	is available in	the storage arena, then	realloc	will ask
     malloc to enlarge the arena by size bytes and will	then move the data to
     the new space.  If	ptr is NULL, realloc behaves like malloc(size).	 If
     size is zero, the storage associated with ptr is freed and	realloc
     returns the same result as	does malloc(0).

     calloc allocates space for	an array of nelem elements of size elsize.
     The space is initialized to zeros.

     memalign allocates	size bytes on a	specified alignment boundary and
     returns a pointer to the allocated	block.	The value of the returned
     address is	guaranteed to be a multiple of alignment.  Note	that the value
     of	alignment must be a power of two and must be greater than or equal to

									Page 1

MALLOC(3C)							    MALLOC(3C)

     the size of a word, or, for 64 bit	objects, the size of a doubleword.

     valloc(size) is equivalent	to memalign(sysconf(_SC_PAGESIZE),size). For
     more information see sysconf(3c).

     Each of the allocation routines returns a pointer to space	suitably
     aligned (after possible pointer coercion) for storage of any type of

SEE ALSO    [Toc]    [Back]

     brk(2), sysconf(3c), malloc(3X)

DIAGNOSTICS    [Toc]    [Back]

     malloc, realloc, calloc, memalign,	and valloc return a NULL pointer if
     there is no available memory or if	the arena has been detectably
     corrupted by storing outside the bounds of	a block.  When this happens
     the block pointed to by ptr may be	destroyed.

NOTES    [Toc]    [Back]

     How an application	manages	its heap can greatly affect the	performance of
     these routines. For most applications, this set will perform well.	 For
     some applications,	the more flexible malloc(3X) package might be more

     A SEGV or Bus Error inside	the malloc routine is almost certainly caused
     by	a previous memory overwrite by the user. This is a delayed error which
     is	caused by a previous overwrite of unallocated memory and is not	a bug
     in	malloc itself.

     When called with size of zero, malloc returns a valid pointer to a	block
     of	zero bytes.  Storage into a block of length zero will corrupt the
     malloc arena and may have serious consequences.

     Products, libraries, or commands that provide their own malloc package
     must provide all of the entry points listed above,	or the normal libc
     malloc entry point	for the	unimplemented routine(s) may be	called
     instead, leading to corrupted heaps, since	it is unlikely that the
     internal details of the heap management will be the same.	If the malloc
     package is	also intended to replace malloc(3X), it	must also provide the
     additional	routines listed	there.

									PPPPaaaaggggeeee 2222
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