UNGETWC(3)                 POSIX Programmer's Manual                UNGETWC(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
       ungetwc -- push wide-character code back into the input stream

SSYYNNOOPPSSIISS
       #include <stdio.h>
       #include <wchar.h>

       wint_t ungetwc(wint_t _w_c, FILE *_s_t_r_e_a_m);

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 _u_n_g_e_t_w_c() function shall push the character corresponding to the
       wide-character code specified by _w_c back onto the input stream pointed
       to by _s_t_r_e_a_m.  The pushed-back characters shall be returned by
       subsequent reads on that stream in the reverse order of their pushing.
       A successful intervening call (with the stream pointed to by _s_t_r_e_a_m) to
       a file-positioning function (_f_s_e_e_k(), _f_s_e_e_k_o(), _f_s_e_t_p_o_s(), or _r_e_w_i_n_d())
       or _f_f_l_u_s_h() shall discard any pushed-back characters for the stream.
       The external storage corresponding to the stream is unchanged.

       At least one character of push-back shall be provided. If _u_n_g_e_t_w_c() is
       called too many times on the same stream without an intervening read or
       file-positioning operation on that stream, the operation may fail.

       If the value of _w_c equals that of the macro WEOF, the operation shall
       fail and the input stream shall be left unchanged.

       A successful call to _u_n_g_e_t_w_c() shall clear the end-of-file indicator
       for the stream. The value of the file-position indicator for the stream
       after all pushed-back characters have been read, or discarded by
       calling _f_s_e_e_k(), _f_s_e_e_k_o(), _f_s_e_t_p_o_s(), or _r_e_w_i_n_d() (but not _f_f_l_u_s_h()),
       shall be the same as it was before the characters were pushed back. The
       file-position indicator is decremented (by one or more) by each
       successful call to _u_n_g_e_t_w_c(); if its value was 0 before a call, its
       value is unspecified after the call.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, _u_n_g_e_t_w_c() shall return the wide-character
       code corresponding to the pushed-back character. Otherwise, it shall
       return WEOF.

EERRRROORRSS
       The _u_n_g_e_t_w_c() function may fail if:

       EEIILLSSEEQQ An invalid character sequence is detected, or a wide-character
              code does not correspond to a valid character.

       _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
       None.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _S_e_c_t_i_o_n _2_._5, _S_t_a_n_d_a_r_d _I_/_O _S_t_r_e_a_m_s, _f_s_e_e_k(), _f_s_e_t_p_o_s(), _r_e_a_d(),
       _r_e_w_i_n_d(), _s_e_t_b_u_f()

       The Base Definitions volume of POSIX.1-2017, <<ssttddiioo..hh>>, <<wwcchhaarr..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                           UNGETWC(3)
