PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       realloc — memory reallocator

SYNOPSIS

       #include <stdlib.h>

       void *realloc(void *ptr, size_t size);

DESCRIPTION

       The  functionality  described  on  this  reference  page is aligned with the ISO C standard. Any conflict
       between the requirements described  here  and  the  ISO C  standard  is  unintentional.  This  volume  of
       POSIX.1‐2008 defers to the ISO C standard.

       The  realloc()  function  shall deallocate the old object pointed to by ptr and return a pointer to a new
       object that has the size specified by size.  The contents of the new object shall be the same as that  of
       the  old  object  prior  to deallocation, up to the lesser of the new and old sizes. Any bytes in the new
       object beyond the size of the old object have indeterminate values. If the size of the space requested is
       zero, the behavior shall be implementation-defined: either a null pointer is returned,  or  the  behavior
       shall  be  as if the size were some non-zero value, except that the returned pointer shall not be used to
       access an object. If the space cannot be allocated, the object shall remain unchanged.

       If ptr is a null pointer, realloc() shall be equivalent to malloc() for the specified size.

       If ptr does not match a pointer returned earlier by calloc(), malloc(), or realloc() or if the space  has
       previously been deallocated by a call to free() or realloc(), the behavior is undefined.

       The  order  and  contiguity  of  storage  allocated  by successive calls to realloc() is unspecified. The
       pointer returned if the allocation succeeds shall be suitably aligned so that it may  be  assigned  to  a
       pointer  to  any  type of object and then used to access such an object in the space allocated (until the
       space is explicitly freed or reallocated). Each such allocation  shall  yield  a  pointer  to  an  object
       disjoint  from  any  other object. The pointer returned shall point to the start (lowest byte address) of
       the allocated space. If the space cannot be allocated, a null pointer shall be returned.

RETURN VALUE

       Upon successful completion, realloc() shall return a pointer to the (possibly moved) allocated space.  If
       size is 0, either:

        *  A null pointer shall be returned and errno set to an implementation-defined value.

        *  A  unique  pointer that can be successfully passed to free() shall be returned, and the memory object
           pointed to by ptr shall be freed. The application shall ensure that the pointer is not used to access
           an object.

       If there is not enough available memory, realloc() shall return a null pointer and set errno to [ENOMEM].
       If realloc() returns a null pointer and errno has been set to [ENOMEM],  the  memory  referenced  by  ptr
       shall not be changed.

ERRORS

       The realloc() function shall fail if:

       ENOMEM Insufficient memory is available.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The  description of realloc() has been modified from previous versions of this standard to align with the
       ISO/IEC 9899:1999 standard. Previous versions explicitly permitted a call to realloc(p, 0)  to  free  the
       space pointed to by p and return a null pointer. While this behavior could be interpreted as permitted by
       this  version  of  the  standard,  the  C  language  committee have indicated that this interpretation is
       incorrect. Applications should assume that if realloc() returns a null pointer, the space pointed to by p
       has not been freed. Since this could lead to double-frees, implementations should also  set  errno  if  a
       null  pointer  actually  indicates  a  failure,  and applications should only free the space if errno was
       changed.

RATIONALE

       None.

FUTURE DIRECTIONS

       This standard defers to the ISO C standard. While that standard currently has language that might  permit
       realloc(p,  0),  where  p  is  not  a  null  pointer, to free p while still returning a null pointer, the
       committee responsible for that standard is considering clarifying the  language  to  explicitly  prohibit
       that alternative.

SEE ALSO

       calloc(), free(), malloc()

       The Base Definitions volume of POSIX.1‐2008, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event
       of any discrepancy between this version and the original IEEE and The Open Group Standard,  the  original
       IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at
       http://www.unix.org/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2013                                       REALLOC(3POSIX)