UNGETC(P) POSIX Programmer's Manual UNGETC(P)NAMEungetc - push byte back into input stream
SYNOPSIS
#include <stdio.h>
int ungetc(int c, FILE *stream);
DESCRIPTION
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(), fsetpos(), or rewind()) 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-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 reading or discarding all pushed-back bytes 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 ALSOfseek() , getc() , fsetpos() , read() , rewind() , setbuf() , the Base
Definitions volume of IEEE Std 1003.1-2001, <stdio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
IEEE/The Open Group 2003 UNGETC(P)
