HardenedBSD/lib/libc/stdio/ungetc.3
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.\" Copyright (c) 1990, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Chris Torek and the American National Standards Committee X3,
.\" on Information Processing Systems.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\"
.Dd June 4, 1993
.Dt UNGETC 3
.Os
.Sh NAME
.Nm ungetc
.Nd un-get character from input stream
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft int
.Fn ungetc "int c" "FILE *stream"
.Sh DESCRIPTION
The
.Fn ungetc
function pushes the character
.Fa c
(converted to an unsigned char)
back onto the input stream pointed to by
.Fa stream .
The pushed-back characters will be returned by subsequent reads on the
stream (in reverse order).
A successful intervening call,
using the same stream,
to one of the file positioning functions
.Xr ( fseek 3 ,
.Xr fsetpos 3 ,
or
.Xr rewind 3 )
will discard the pushed back characters.
.Pp
One character of push-back is guaranteed,
but as long as there is sufficient memory,
an effectively infinite amount of pushback is allowed.
.Pp
If a character is successfully pushed-back,
the end-of-file indicator for the stream is cleared.
The file-position indicator is decremented
by each successful call to
.Fn ungetc ;
if its value was 0 before a call, its value is unspecified after
the call.
.Sh RETURN VALUES
The
.Fn ungetc
function returns the character pushed-back after the conversion,
or
.Dv EOF
if the operation fails.
If the value of the argument
.Fa c
character equals
.Dv EOF ,
the operation will fail and the stream will remain unchanged.
.Sh SEE ALSO
.Xr fseek 3 ,
.Xr getc 3 ,
.Xr setvbuf 3 ,
.Xr ungetwc 3
.Sh STANDARDS
The
.Fn ungetc
function conforms to
.St -isoC .