ungetc(3p) — Linux manual page


UNGETC(3P)                POSIX Programmer's Manual               UNGETC(3P)

PROLOG         top

       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         top

       ungetc — push byte back into input stream

SYNOPSIS         top

       #include <stdio.h>

       int ungetc(int c, FILE *stream);

DESCRIPTION         top

       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 ungetc() function shall push the byte specified by c (converted
       to an unsigned char) back onto the input stream pointed to by stream.
       The pushed-back bytes 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 stream) to a file-
       positioning function (fseek(), fseeko(), fsetpos(), or rewind()) or
       fflush() shall discard any pushed-back bytes for the stream. The
       external storage corresponding to the stream shall be unchanged.

       One byte of push-back shall be provided. If ungetc() 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 c equals that of the macro EOF, the operation shall
       fail and the input stream shall be left unchanged.

       A successful call to ungetc() shall clear the end-of-file indicator
       for the stream. The value of the file-position indicator for the
       stream after all pushed-back bytes have been read, or discarded by
       calling fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()),
       shall be the same as it was before the bytes were pushed back. The
       file-position indicator is decremented by each successful call to
       ungetc(); if its value was 0 before a call, its value is unspecified
       after the call.

RETURN VALUE         top

       Upon successful completion, ungetc() shall return the byte pushed
       back after conversion. Otherwise, it shall return EOF.

ERRORS         top

       No errors are defined.

       The following sections are informative.

EXAMPLES         top




RATIONALE         top




SEE ALSO         top

       Section 2.5, Standard I/O Streams, fseek(3p), getc(3p), fsetpos(3p),
       read(3p), rewind(3p), setbuf(3p)

       The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)

COPYRIGHT         top

       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                          UNGETC(3P)

Pages that refer to this page: stdio.h(0p)fgetc(3p)fgetpos(3p)fgets(3p)fseek(3p)fseeko(3p)fsetpos(3p)stderr(3p)stdin(3p)stdout(3p)