.\" 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. .\" 4. 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 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)ungetc.3 8.1 (Berkeley) 6/4/93 .\" $FreeBSD: src/lib/libc/stdio/ungetc.3,v 1.14 2007/01/09 00:28:07 imp Exp $ .\" .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 .Fo ungetc .Fa "int c" .Fa "FILE *stream" .Fc .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 (in reverse order) by subsequent reads on the stream. A successful intervening call to one of the file positioning functions .Xr ( fseek 3 , .Xr fsetpos 3 , or .Xr rewind 3 ) , using the same stream, will discard the pushed-back characters. .Pp Only one character of push-back is guaranteed, but as long as there is sufficient memory, an effectively infinite amount of push-back 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 .