malloc
, realloc
, free
---manage memory#include <stdlib.h> void *malloc(size_t nbytes); void *realloc(void *aptr, size_t nbytes); void free(void *aptr); void *_malloc_r(void *reent, size_t nbytes); void *_realloc_r(void *reent, void *aptr, size_t nbytes); void _free_r(void *reent, void *aptr);Description
Use malloc
to request allocation of an object with at least
nbytes bytes of storage available. If the space is available,
malloc
returns a pointer to a newly allocated block as its result.
If you already have a block of storage allocated by malloc
, but
you no longer need all the space allocated to it, you can make it
smaller by calling realloc
with both the object pointer and the
new desired size as arguments. realloc
guarantees that the
contents of the smaller object match the beginning of the original object.
Similarly, if you need more space for an object, use realloc
to
request the larger size; again, realloc
guarantees that the
beginning of the new, larger object matches the contents of the
original object.
When you no longer need an object originally allocated by malloc
or realloc
(or the related function calloc
), return it to the
memory storage pool by calling free
with the address of the object
as the argument. You can also use realloc
for this purpose by
calling it with 0
as the nbytes argument.
The alternate functions _malloc_r
, _realloc_r
, and _free_r
are reentrant versions. The extra argument reent is a pointer to
a reentrancy structure.
Returns
malloc
returns a pointer to the newly allocated space, if
successful; otherwise it returns NULL
. If your application needs
to generate empty objects, you may use malloc(0)
for this purpose.
realloc
returns a pointer to the new block of memory, or NULL
if a new block could not be allocated. NULL
is also the result
when you use `realloc(aptr,0)
' (which has the same effect as
`free(aptr)
'). You should always check the result of
realloc
; successful reallocation is not guaranteed even when
you request a smaller object.
free
does not return a result.
Portability
malloc
, realloc
, and free
are specified by the ANSI C
standard, but other conforming implementations of malloc
may
behave differently when nbytes is zero.
Supporting OS subroutines required: sbrk
, write
(if WARN_VLIMIT).