1.\" $OpenBSD: ungetc.3,v 1.7 2007/05/31 19:19:31 jmc Exp $ 2.\" 3.\" Copyright (c) 1990, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" Chris Torek and the American National Standards Committee X3, 8.\" on Information Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.Dd $Mdocdate: May 31 2007 $ 35.Dt UNGETC 3 36.Os 37.Sh NAME 38.Nm ungetc 39.Nd un-get character from input stream 40.Sh SYNOPSIS 41.Fd #include <stdio.h> 42.Ft int 43.Fn ungetc "int c" "FILE *stream" 44.Sh DESCRIPTION 45The 46.Fn ungetc 47function pushes the character 48.Fa c 49(converted to an 50.Li unsigned char ) 51back onto the input stream pointed to by 52.Fa stream . 53The pushed-backed characters will be returned by subsequent reads on the 54stream (in reverse order). 55A successful intervening call, using the same stream, to one of the file 56positioning functions 57.Po 58.Xr fseek 3 , 59.Xr fsetpos 3 , 60or 61.Xr rewind 3 62.Pc 63will discard the pushed back characters. 64.Pp 65One character of push-back is guaranteed, 66but as long as there is 67sufficient memory, an effectively infinite amount of pushback is allowed. 68.Pp 69If a character is successfully pushed-back, 70the end-of-file indicator for the stream is cleared. 71.Sh RETURN VALUES 72The 73.Fn ungetc 74function returns the character pushed-back after the conversion, or 75.Dv EOF 76if the operation fails. 77If the value of the argument 78.Fa c 79character equals 80.Dv EOF , 81the operation will fail and the stream will remain unchanged. 82.Sh SEE ALSO 83.Xr fseek 3 , 84.Xr getc 3 , 85.Xr setvbuf 3 86.Sh STANDARDS 87The 88.Fn ungetc 89function conforms to 90.St -ansiC . 91