1.\" $NetBSD: ungetc.3,v 1.10 2010/04/30 05:56:14 jruoho 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.\" @(#)ungetc.3 8.1 (Berkeley) 6/4/93 35.\" 36.Dd April 30, 2010 37.Dt UNGETC 3 38.Os 39.Sh NAME 40.Nm ungetc 41.Nd un-get character from input stream 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In 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 unsigned char) 54back onto the input stream pointed to by 55.Fa stream . 56The pushed-backed characters will be returned by subsequent reads on the 57stream (in reverse order). 58A successful intervening call, using the same stream, to one of the file 59positioning functions 60.Po 61.Xr fseek 3 , 62.Xr fsetpos 3 , 63or 64.Xr rewind 3 65.Pc 66will discard the pushed back characters. 67.Pp 68One character of push-back is guaranteed, 69but as long as there is 70sufficient memory, an effectively infinite amount of pushback is allowed. 71.Pp 72If a character is successfully pushed-back, 73the end-of-file indicator for the stream is cleared. 74.Sh RETURN VALUES 75The 76.Fn ungetc 77function 78returns 79the character pushed-back after the conversion, or 80.Dv EOF 81if the operation fails. 82If the value of the argument 83.Fa c 84character equals 85.Dv EOF , 86the operation will fail and the stream will remain unchanged. 87.Sh SEE ALSO 88.Xr fseek 3 , 89.Xr getc 3 , 90.Xr setvbuf 3 91.Sh STANDARDS 92The 93.Fn ungetc 94function conforms to 95.St -ansiC 96and 97.St -p1003.1-2001 . 98.Sh HISTORY 99An 100.Fn ungetc 101function appeared in 102.At v7 . 103