MALLOC(3C) | Standard C Library Functions | MALLOC(3C) |
malloc
, calloc
,
free
, freezero
,
memalign
, realloc
,
reallocf
, reallocarray
,
recallocarray
, valloc
,
alloca
—
#include <stdlib.h>
void *
malloc
(size_t size);
void *
calloc
(size_t nelem,
size_t elsize);
void
free
(void *ptr);
void
freezero
(void *ptr,
size_t size);
void *
memalign
(size_t alignment,
size_t size);
void *
realloc
(void *ptr,
size_t size);
void *
reallocf
(void *ptr,
size_t size);
void *
reallocarray
(void *ptr,
size_t nelem, size_t
elsize);
void *
recallocarray
(void *ptr,
size_t oldnelem, size_t
newnelem, size_t elsize);
void *
valloc
(size_t size);
#include
<alloca.h>
void *
alloca
(size_t size);
malloc
() and free
()
functions provide a simple, general-purpose memory allocation package. The
malloc
() function returns a pointer to a block of at
least size bytes suitably aligned for any use. If the
space assigned by malloc
() is overrun, the results are
undefined.
The argument to free
() is a pointer to a
block previously allocated by malloc
(),
calloc
(), realloc
(),
reallocf
(), reallocarray
(),
or recallocarray
(). After
free
() is executed, this space is made available for
further allocation by the application, though not returned to the system.
Memory is returned to the system only upon termination of the application.
If ptr is a null pointer, no action occurs. If a
random number is passed to free
(), the results are
undefined.
The freezero
() function is similar to the
free
() function except it ensures memory is
explicitly discarded. If ptr is
NULL
, no action occurs. If ptr
is not NULL
, the size argument
must be equal or smaller than the size of the earlier allocation that
returned ptr. freezero
()
guarantees the memory range starting at ptr with
length size is discarded while deallocating the whole
object originally allocated.
The calloc
() function allocates space for
an array of nelem elements of size
elsize. The space is initialized to zeros.
The memalign
() function 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 an even multiple of alignment. The
value of alignment must be a power of two and must be
greater than or equal to the size of a word.
The realloc
() function 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 the new size of the block requires movement of the block, the
space for the previous instantiation of the block is freed. If the new size
is larger, the contents of the newly allocated portion of the block are
unspecified. If ptr is NULL
,
realloc
() behaves like
malloc
() for the specified size. If
size is 0 and ptr is not a null
pointer, the space pointed to is freed.
The reallocf
() function behaves in the
same way as realloc
() except that the passed pointer
is freed automatically on failure.
The reallocarray
() function is similar to
realloc
(), but operates on
nelem elements of size elsize
and checks for overflow in
nelem*elsize calculation.
The recallocarray
() function is similar to
reallocarray
() except it ensures newly allocated
memory is cleared similar to calloc
(). If
ptr is NULL
,
oldnelem is ignored and the call is equivalent to
calloc
(). If ptr is not
NULL
, oldnelem must be a value
such that oldnelem*elsize is the
size of the earlier allocation that returned ptr,
otherwise the behaviour is undefined.
The valloc
() function has the same effect
as malloc
(), except that the allocated memory will
be aligned to a multiple of the value returned by
sysconf
(_SC_PAGESIZE
).
The alloca
() function allocates
size bytes of space in the stack frame of the caller,
and returns a pointer to the allocated block. This temporary space is
automatically freed when the caller returns. If the allocated block is
beyond the current stack limit, the resulting behavior is undefined.
If there is no available memory, malloc
(),
calloc
(), realloc
(),
reallocf
(), reallocarray
(),
recallocarray
(), memalign
(),
and valloc
() return a null pointer.
When realloc
() is called with
size > 0 and returns NULL
,
the block pointed to by ptr is left intact. By
contrast, when reallocf
() is called with
size > 0 and returns NULL
,
the block pointed to by ptr will have been freed.
If size, nelem, or
elsize is 0, either a null pointer or a unique pointer
that can be passed to free
() is returned.
If malloc
(),
calloc
(), realloc
(),
reallocf
(), reallocarray
(),
or recallocarray
() returns unsuccessfully,
errno will be set to indicate the error. The
free
() and freezero
()
functions do not set errno.
malloc
(), calloc
(),
realloc
(), reallocf
(), and
reallocarray
() functions will fail if:
ENOMEM
reallocarray
().EAGAIN
The recallocarray
() function will fail
if:
EINVAL
NULL
and
multiplying oldnelem and
elsize results in integer overflow.valloc
() but
should instead use malloc
() or
mmap(2). On systems with a large page
size, the number of successful valloc
() operations
might be 0.
These default memory allocation routines are safe for use in multithreaded applications but are not scalable. Concurrent accesses by multiple threads are single-threaded through the use of a single lock. Multithreaded applications that make heavy use of dynamic memory allocation should be linked with allocation libraries designed for concurrent access, such as libumem(3LIB) or libmtmalloc(3LIB). Applications that want to avoid using heap allocations (with brk(2)) can do so by using either libumem(3LIB) or libmapmalloc(3LIB). The allocation libraries libmalloc(3LIB) and libbsdmalloc(3LIB) are available for special needs.
Comparative features of the various allocation libraries can be found in the umem_alloc(3MALLOC) manual page.
malloc
(), calloc
(),
free
(), realloc
(),
valloc
() functions are Standard.
The freezero
(),
reallocf
(), reallocarray
(),
and recallocarray
() functions are
Committed.
The memalign
() and
alloca
() functions are Stable.
The alloca
() function is machine-,
compiler-, and most of all, system-dependent. Its use is strongly
discouraged.
September 12, 2019 | OmniOS |