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

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

       #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);

       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().
       Otherwise, 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().

       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 realloc()
       fails the original block is left untouched - it is not freed or moved.


       brk(2), posix_memalign(3)

       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
       variables.  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
       memory 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

GNU                               1993-04-04                         MALLOC(3)


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