MEMORY(3) BSD Library Functions Manual MEMORY(3)NAME
malloc, free, realloc, calloc, alloca -- general memory allocation operations
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
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);
DESCRIPTION
These functions allocate and free memory for the calling process. They are described in the individual manual pages. The memory allocators
used in the kernel are described in memoryallocators(9).
SEE ALSO alloca(3), calloc(3), free(3), malloc(3), realloc(3)STANDARDS
These functions, with the exception of alloca() conform to ANSI X3.159-1989 (``ANSI C89'').
BSD September 11, 2011 BSD
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MALLOC(3) BSD Library Functions Manual MALLOC(3)NAME
malloc, calloc, realloc, free -- general purpose memory allocation functions
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
void *
malloc(size_t size);
void *
calloc(size_t number, size_t size);
void *
realloc(void *ptr, size_t size);
void
free(void *ptr);
DESCRIPTION
The malloc() function allocates size bytes of uninitialized memory. The allocated space is suitably aligned (after possible pointer coer-
cion) for storage of any type of object.
The calloc() function allocates space for number objects, each size bytes in length. The result is identical to calling malloc() with an
argument of ``number * size'', with the exception that the allocated memory is explicitly initialized to zero bytes.
The realloc() function changes the size of the previously allocated memory referenced by ptr to size bytes. The contents of the memory are
unchanged up to the lesser of the new and old sizes. If the new size is larger, the value of the newly allocated portion of the memory is
undefined. Upon success, the memory referenced by ptr is freed and a pointer to the newly allocated memory is returned. Note that realloc()
may move the memory allocation, resulting in a different return value than ptr. If ptr is NULL, the realloc() function behaves identically
to malloc() for the specified size.
The free() function causes the allocated memory referenced by ptr to be made available for future allocations. If ptr is NULL, no action
occurs.
RETURN VALUES
The malloc() and calloc() functions return a pointer to the allocated memory if successful; otherwise a NULL pointer is returned and errno is
set to ENOMEM.
The realloc() function returns a pointer, possibly identical to ptr, to the allocated memory if successful; otherwise a NULL pointer is
returned, and errno is set to ENOMEM if the error was the result of an allocation failure. The realloc() function always leaves the original
buffer intact when an error occurs.
The free() function returns no value.
EXAMPLES
When using malloc(), be careful to avoid the following idiom:
if ((p = malloc(number * size)) == NULL)
err(EXIT_FAILURE, "malloc");
The multiplication may lead to an integer overflow. To avoid this, calloc() is recommended.
If malloc() must be used, be sure to test for overflow:
if (size && number > SIZE_MAX / size) {
errno = EOVERFLOW;
err(EXIT_FAILURE, "allocation");
}
When using realloc(), one must be careful to avoid the following idiom:
nsize += 50;
if ((p = realloc(p, nsize)) == NULL)
return NULL;
Do not adjust the variable describing how much memory has been allocated until it is known that the allocation has been successful. This can
cause aberrant program behavior if the incorrect size value is used. In most cases, the above example will also leak memory. As stated ear-
lier, a return value of NULL indicates that the old object still remains allocated. Better code looks like this:
newsize = size + 50;
if ((p2 = realloc(p, newsize)) == NULL) {
if (p != NULL)
free(p);
p = NULL;
return NULL;
}
p = p2;
size = newsize;
SEE ALSO madvise(2), mmap(2), sbrk(2), alloca(3), atexit(3), getpagesize(3), memory(3), posix_memalign(3)
For the implementation details, see jemalloc(3).
STANDARDS
The malloc(), calloc(), realloc() and free() functions conform to ISO/IEC 9899:1990 (``ISO C90'').
BSD May 3, 2010 BSD