malloc, free, realloc, calloc, alloca - memory allocator
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 *alloca(size_t size)
Malloc and free provide a general-purpose memory allocation package.
Malloc returns a pointer to a block of at least size bytes beginning on a
The argument to free is a pointer to a block previously allocated by
malloc; this space is made available for further allocation, but its
contents are left undisturbed. A call with a null ptr is legal and does
Needless to say, grave disorder will result if the space assigned by
malloc is overrun or if some random number is handed to free.
Malloc maintains multiple lists of free blocks according to size,
allocating space from the appropriate list. It calls sbrk (see brk(2))
to get more memory from the system when there is no suitable space
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. A call with a null
ptr is legal and has the same result as malloc(size).
Calloc allocates space for an array of nelem elements of size elsize. The
space is initialized to zeros.
Alloca allocates size bytes of space in the stack frame of the caller.
This temporary space is automatically freed on return.
Each of the allocation routines returns a pointer to space suitably
aligned (after possible pointer coercion) for storage of any type of
Malloc, realloc and calloc 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.
Other implementations of malloc, realloc or calloc may return a null
pointer if the size of the requested block is zero. This implementation
will always return a zero length block at a unique address, but you
should keep in mind that a null return is possible if the program is run
to another system and that this should not be mistakenly seen as an
When realloc returns a null pointer, the block pointed to by ptr may be
Alloca is machine dependent; its use is discouraged.