1.\" $OpenBSD: ungetc.3,v 1.5 2000/12/24 00:30:59 aaron 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. All advertising materials mentioning features or use of this software 19.\" must display the following acknowledgement: 20.\" This product includes software developed by the University of 21.\" California, Berkeley and its contributors. 22.\" 4. Neither the name of the University nor the names of its contributors 23.\" may be used to endorse or promote products derived from this software 24.\" without specific prior written permission. 25.\" 26.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36.\" SUCH DAMAGE. 37.\" 38.Dd June 4, 1993 39.Dt UNGETC 3 40.Os 41.Sh NAME 42.Nm ungetc 43.Nd un-get character from input stream 44.Sh SYNOPSIS 45.Fd #include <stdio.h> 46.Ft int 47.Fn ungetc "int c" "FILE *stream" 48.Sh DESCRIPTION 49The 50.Fn ungetc 51function pushes the character 52.Fa c 53(converted to an 54.Li unsigned char ) 55back onto the input stream pointed to by 56.Fa stream . 57The pushed-backed characters will be returned by subsequent reads on the 58stream (in reverse order). 59A successful intervening call, using the same stream, to one of the file 60positioning functions 61.Po 62.Xr fseek 3 , 63.Xr fsetpos 3 , 64or 65.Xr rewind 3 66.Pc 67will discard the pushed back characters. 68.Pp 69One character of push-back is guaranteed, 70but as long as there is 71sufficient memory, an effectively infinite amount of pushback is allowed. 72.Pp 73If a character is successfully pushed-back, 74the end-of-file indicator for the stream is cleared. 75.Sh RETURN VALUES 76The 77.Fn ungetc 78function returns the character pushed-back after the conversion, or 79.Dv EOF 80if the operation fails. 81If the value of the argument 82.Fa c 83character equals 84.Dv EOF , 85the operation will fail and the stream will remain unchanged. 86.Sh SEE ALSO 87.Xr fseek 3 , 88.Xr getc 3 , 89.Xr setvbuf 3 90.Sh STANDARDS 91The 92.Fn ungetc 93function conforms to 94.St -ansiC . 95