UNGETC(3P) POSIX Programmer's Manual UNGETC(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.
NAMEungetc — push byte back into input stream
SYNOPSIS
#include <stdio.h>
int ungetc(int c, FILE *stream);
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 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 correspond‐
ing 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-position‐
ing 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
Upon successful completion, ungetc() shall return the byte pushed back
after conversion. Otherwise, it shall return EOF.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5, Standard I/O Streams, fseek(), getc(), fsetpos(), read(),
rewind(), setbuf()
The Base Definitions volume of POSIX.1‐2008, <stdio.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 UNGETC(3P)
