MALLOC(3)						     Linux Programmer's Manual							 MALLOC(3)

NAME

       calloc, malloc, free, realloc - Allocate and free dynamic memory

SYNOPSIS

       #include <stdlib.h>

       void *calloc(size_t nmemb, size_t size);
       void *malloc(size_t size);
       void free(void *ptr);
       void *realloc(void *ptr, size_t size);

DESCRIPTION

       calloc()  allocates  memory for an array of nmemb elements of size bytes each and returns a pointer to the allocated memory.  The memory is
       set to zero.

       malloc() allocates size bytes and returns a pointer to the allocated memory.  The memory is not cleared.

       free() frees the memory space pointed to by ptr, which must have been returned by a previous call to malloc(), calloc() or realloc().  Oth-
       erwise, or if free(ptr) has already been called before, undefined behaviour occurs.  If ptr is NULL, no operation is performed.

       realloc()  changes  the size of the memory block pointed to by ptr to size bytes.  The contents will be unchanged to the minimum of the old
       and new sizes; newly allocated memory will be uninitialized.  If ptr is NULL, the call is equivalent to malloc(size); if size is  equal	to
       zero,  the  call  is  equivalent  to free(ptr).	Unless ptr is NULL, it must have been returned by an earlier call to malloc(), calloc() or
       realloc().

RETURN VALUE

       For calloc() and malloc(), the value returned is a pointer to the allocated memory, which is suitably aligned for any kind of variable,	or
       NULL if the request fails.

       free() returns no value.

       realloc()  returns  a  pointer  to the newly allocated memory, which is suitably aligned for any kind of variable and may be different from
       ptr, or NULL if the request fails. If size was equal to 0, either NULL or a pointer suitable to be passed to free() is returned.  If  real-
       loc() fails the original block is left untouched - it is not freed or moved.

CONFORMING TO

       ANSI-C

SEE ALSO

       brk(2), posix_memalign(3)

NOTES

       The  Unix98  standard  requires malloc(), calloc(), and realloc() to set errno to ENOMEM upon failure. Glibc assumes that this is done (and
       the glibc versions of these routines do this); if you use a private malloc implementation that does not set  errno,  then  certain  library
       routines may fail without having a reason in errno.

       Crashes	in  malloc(),  free() or realloc() are almost always related to heap corruption, such as overflowing an allocated chunk or freeing
       the same pointer twice.

       Recent versions of Linux libc (later than 5.4.23) and GNU libc (2.x) include a malloc implementation which is tunable via environment vari-
       ables.	When  MALLOC_CHECK_  is  set,  a  special  (less efficient) implementation is used which is designed to be tolerant against simple
       errors, such as double calls of free() with the same argument, or overruns of a single byte (off-by-one bugs).  Not all such errors can	be
       protected  against,  however, and memory leaks can result.  If MALLOC_CHECK_ is set to 0, any detected heap corruption is silently ignored;
       if set to 1, a diagnostic is printed on stderr; if set to 2, abort() is called immediately.  This can be useful because otherwise  a  crash
       may happen much later, and the true cause for the problem is then very hard to track down.

       Linux follows an optimistic memory allocation strategy.	This means that when malloc() returns non-NULL there is no guarantee that the mem-
       ory really is available. In case it turns out that the system is out of memory, one or more processes will be killed by	the  infamous  OOM
       killer.

GNU
								    1993-04-04								 MALLOC(3)