REALLOC(3)                 POSIX Programmer's Manual                REALLOC(3)



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

NNAAMMEE
       realloc -- memory reallocator

SSYYNNOOPPSSIISS
       #include <stdlib.h>

       void *realloc(void *_p_t_r, size_t _s_i_z_e);

DDEESSCCRRIIPPTTIIOONN
       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.1-2017
       defers to the ISO C standard.

       The _r_e_a_l_l_o_c() function shall deallocate the old object pointed to by
       _p_t_r and return a pointer to a new object that has the size specified by
       _s_i_z_e.  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 behavior is undefined if the returned pointer is
       used to access an object. If the space cannot be allocated, the object
       shall remain unchanged.

       If _p_t_r is a null pointer, _r_e_a_l_l_o_c() shall be equivalent to _m_a_l_l_o_c() for
       the specified size.

       If _p_t_r does not match a pointer returned earlier by _c_a_l_l_o_c(), _m_a_l_l_o_c(),
       or _r_e_a_l_l_o_c() or if the space has previously been deallocated by a call
       to _f_r_e_e() or _r_e_a_l_l_o_c(), the behavior is undefined.

       The order and contiguity of storage allocated by successive calls to
       _r_e_a_l_l_o_c() 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.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, _r_e_a_l_l_o_c() shall return a pointer to the
       (possibly moved) allocated space. If _s_i_z_e is 0, either:

        *  A null pointer shall be returned and, if _p_t_r is not a null pointer,
           _e_r_r_n_o shall be set to an implementation-defined value.

        *  A pointer to the allocated space shall be returned, and the memory
           object pointed to by _p_t_r shall be freed. The application shall
           ensure that the pointer is not used to access an object.

       If there is not enough available memory, _r_e_a_l_l_o_c() shall return a null
       pointer and set _e_r_r_n_o to [[EENNOOMMEEMM]].  If _r_e_a_l_l_o_c() returns a null pointer
       and _e_r_r_n_o has been set to [[EENNOOMMEEMM]], the memory referenced by _p_t_r shall
       not be changed.

EERRRROORRSS
       The _r_e_a_l_l_o_c() function shall fail if:

       EENNOOMMEEMM Insufficient memory is available.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       The description of _r_e_a_l_l_o_c() 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 _r_e_a_l_l_o_c(_p_, _0_) _t_o _f_r_e_e _t_h_e _s_p_a_c_e
       _p_o_i_n_t_e_d _t_o _b_y _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 _r_e_a_l_l_o_c() 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 _e_r_r_n_o if a null
       pointer actually indicates a failure, and applications should only free
       the space if _e_r_r_n_o was changed.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       This standard defers to the ISO C standard. While that standard
       currently has language that might permit _r_e_a_l_l_o_c(_p_, _0_)_, _w_h_e_r_e _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.

SSEEEE AALLSSOO
       _c_a_l_l_o_c(), _f_r_e_e(), _m_a_l_l_o_c()

       The Base Definitions volume of POSIX.1-2017, <<ssttddlliibb..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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                  2017                           REALLOC(3)
