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 correspond-
       ing 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  allo-
       cated, 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. Previ-
       ous 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 Technol-
       ogy  --	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 Stan-
       dard 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(3P)