term% cat index.txt MALLOC(2) System Calls Manual MALLOC(2)
NAME
malloc, free, realloc, calloc - memory allocator
SYNOPSIS
#include <u.h>
#include <libc.h>
void* malloc(long size)
void free(void *ptr)
void* realloc(void *ptr, long size)
void* calloc(long nelem, long elsize)
DESCRIPTION
Malloc and free provide a simple memory allocation package. Malloc re‐
turns a pointer to a new block of at least size bytes. The block is
suitably aligned for storage of any type of object. No two active
pointers from malloc will have the same value.
The argument to free is a pointer to a block previously allocated by
malloc; this space is made available for further allocation. It is le‐
gal to free a null pointer; the effect is a no-op.
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. The call real‐
loc(0, size) means the same as
Calloc allocates space for an array of nelem elements of size elsize.
The space is initialized to zeros. Free frees such a block.
Alef
Except for calloc, these routines are available from Alef; they use the
same arena as alloc. Malloc and realloc execute a check when they
fail, rather than return nil. Memory returned by malloc is cleared.
Realloc does not guarantee new memory is cleared unless ptr is nil.
SOURCE
/sys/src/libc/port/malloc.c
SEE ALSO
brk(2)
DIAGNOSTICS
Malloc, realloc and calloc return 0 if there is no available memory.
Errstr is likely to be set.
BUGS
The different specification of calloc is bizarre.
User errors can corrupt the storage arena. The most common gaffes are
(1) freeing an already freed block, (2) storing beyond the bounds of an
allocated block, and (3) freeing data that was not obtained from the
allocator. When malloc and free detect such corruption, they abort.
MALLOC(2)