Standard C Library Functions malloc(3C)
NAME
malloc, calloc, free, memalign, realloc, valloc, alloca -
memory allocator
SYNOPSIS
#include
void *malloc(size_t size);
void *calloc(size_t nelem, size_t elsize);
void free(void *ptr);void *memalign(size_t alignment, size_t size);
void *realloc(void *ptr, size_t size);
void *valloc(size_t size);
#include
void *alloca(size_t size);
DESCRIPTION
The 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 bytessuitably aligned for any use. If the space assigned by mal-
loc() is overrun, the results are undefined. The argument to free() is a pointer to a block previouslyallocated by malloc(), calloc(), or realloc(). After free()
is executed, this space is made available for further allo-
cation by the application, though not returned to the sys-
tem. 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 calloc() function allocates space for an array of nelem
elements of size elsize. The space is initialized to zeros.SunOS 5.11 Last change: 21 Mar 2005 1
Standard C Library Functions malloc(3C)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 pointedto by ptr to size bytes and returns a pointer to the (possi-
bly moved) block. The contents will be unchanged up to the lesser of the new and old sizes. If the new size of theblock requires movement of the block, the space for the pre-
vious instantiation of the block is freed. If the new sizeis 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 valloc() function has the same effect as malloc(),except that the allocated memory will be aligned to a multi-
ple 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 theallocated 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 unde-
fined.RETURN VALUES
Upon successful completion, each of the allocation functions
returns a pointer to space suitably aligned (after possible pointer coercion) for storage of any type of object. If there is no available memory, malloc(), realloc(), memalign(), valloc(), and calloc() return a null pointer. When realloc() is called with size > 0 and returns NULL, the block pointed to by ptr is left intact. 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(), or realloc() returns unsuccessfully, errno will be set to indicate the error. The free() function does not set errno.ERRORS
SunOS 5.11 Last change: 21 Mar 2005 2
Standard C Library Functions malloc(3C) The malloc(), calloc(), and realloc() functions will fail if: ENOMEM The physical limits of the system are exceeded bysize bytes of memory which cannot be allocated.
EAGAIN There is not enough memory available to allocate
size bytes of memory; but the application could try again later.USAGE
Portable applications should avoid using 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. Concurrentaccesses by multiple threads are single-threaded through the
use of a single lock. Multithreaded applications that makeheavy use of dynamic memory allocation should be linked with
allocation libraries designed for concurrent access, such as
libumem(3LIB) or libmtmalloc(3LIB). Applications that wantto avoid using heap allocations (with brk(2)) can do so by
using either libumem or libmapmalloc(3LIB). The allocation
libraries libmalloc(3LIB) and libbsdmalloc(3LIB) are avail-
able for special needs.Comparative features of the various allocation libraries can
be found in the umem_alloc(3MALLOC) manual page.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:SunOS 5.11 Last change: 21 Mar 2005 3
Standard C Library Functions malloc(3C)____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | Safe |
|_____________________________|_____________________________|
| Standard | See below. ||_____________________________|_____________________________|
For malloc(), calloc(), free(), realloc(), and valloc(), see standards(5).SEE ALSO
brk(2), getrlimit(2), libbsdmalloc(3LIB), libmalloc(3LIB), libmapmalloc(3LIB), libmtmalloc(3LIB), libumem(3LIB),umem_alloc(3MALLOC), watchmalloc(3MALLOC), attributes(5),
standards(5) WARNINGS Undefined results will occur if the size requested for a block of memory exceeds the maximum size of a process's heap, which can be obtained with getrlimit(2)The alloca() function is machine-, compiler-, and most of
all, system-dependent. Its use is strongly discouraged.
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