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REALLOC(3P)                POSIX Programmer's Manual               REALLOC(3P)
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 suc-
       ceeds 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 implementa-
           tion-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  lan-
       guage  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  cur-
       rently  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  com-
       mittee responsible for that standard is considering clarifying the lan-
       guage 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 Electri-
       cal 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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                          REALLOC(3P)