term% cat index.txt MALLOC(3) Library Functions Manual MALLOC(3)
NAME
malloc, free, realloc, ialloc, calloc, cfree - main memory allocator
SYNOPSIS
char *malloc(size)
unsigned size;
free(ptr)
char *ptr;
char *realloc(ptr, size)
char *ptr;
unsigned size;
ialloc(ptr, size)
char *ptr;
unsigned size;
char *calloc(nelem, elsize)
unsigned nelem, elsize;
cfree(ptr)
char *ptr;
DESCRIPTION
Malloc and free provide a simple general-purpose memory allocation
package. Malloc returns a pointer to a new block of at least size
bytes.
The argument to free is a pointer to a block previously allocated by
malloc; this space is made available for further allocation. The
present implementation of free does not change the contents; but it is
unwise to depend on this fact.
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.
Ialloc inserts into the arena a designated block of store that was not
previously known to the allocator.
Calloc allocates space for an array of nelem elements of size elsize.
The space is initialized to zeros. Cfree frees such a block.
Each of the allocation routines returns a pointer to space suitably
aligned (after possible pointer coercion) for storage of any type of
object.
The arena, though not necessarily contiguous, is kept in strict address
order. 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 break(2)) to get more memory from the system when there is no
suitable space already free. It has been arranged that realloc will
work on a block that has been freed, provided no other allocations have
intervened. This questionable, unportable practice allows combinations
of free, realloc and malloc to be used to rearrange the arena.
SEE ALSO
galloc(3), sbrk(2)
DIAGNOSTICS
Malloc, realloc and calloc return a null pointer (0) if there is no
available memory or if the arena has been detectably corrupted by stor‐
ing outside the bounds of a block. A very stringently checking version
of malloc, which aborts with a diagnostic if the arena is corrupted,
can be created by recompilation with a debugging flag set; see the
source.
BUGS
When realloc returns 0, the block pointed to by ptr may be destroyed.
Malloc is general, not fast. A program that repeatedly allocates and
frees a particular kind of block often can be speeded up by superimpos‐
ing a block-cacheing or suballocation scheme on top of malloc-free.
MALLOC(3)