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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().  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().

RETURN VALUES

       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  or  if
       size  was equal to 0.  If realloc() fails the original block is left untouched - it is not
       freed or moved.

CONFORMING TO

       ANSI-C

SEE ALSO

       brk(2)

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 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 proteced 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.