1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Chris Torek and the American National Standards Committee X3, 6.\" on Information Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" @(#)ungetc.3 8.1 (Berkeley) 6/4/93 37.\" $FreeBSD: src/lib/libc/stdio/ungetc.3,v 1.4.2.5 2001/12/14 18:33:57 ru Exp $ 38.\" $DragonFly: src/lib/libc/stdio/ungetc.3,v 1.2 2003/06/17 04:26:46 dillon Exp $ 39.\" 40.Dd June 4, 1993 41.Dt UNGETC 3 42.Os 43.Sh NAME 44.Nm ungetc 45.Nd un-get character from input stream 46.Sh LIBRARY 47.Lb libc 48.Sh SYNOPSIS 49.In stdio.h 50.Ft int 51.Fn ungetc "int c" "FILE *stream" 52.Sh DESCRIPTION 53The 54.Fn ungetc 55function pushes the character 56.Fa c 57(converted to an unsigned char) 58back onto the input stream pointed to by 59.Fa stream . 60The pushed-back characters will be returned by subsequent reads on the 61stream (in reverse order). 62A successful intervening call, 63using the same stream, 64to one of the file positioning functions 65.Xr ( fseek 3 , 66.Xr fsetpos 3 , 67or 68.Xr rewind 3 ) 69will discard the pushed back characters. 70.Pp 71One character of push-back is guaranteed, 72but as long as there is sufficient memory, 73an effectively infinite amount of pushback is allowed. 74.Pp 75If a character is successfully pushed-back, 76the end-of-file indicator for the stream is cleared. 77.Sh RETURN VALUES 78The 79.Fn ungetc 80function returns the character pushed-back after the conversion, 81or 82.Dv EOF 83if the operation fails. 84If the value of the argument 85.Fa c 86character equals 87.Dv EOF , 88the operation will fail and the stream will remain unchanged. 89.Sh SEE ALSO 90.Xr fseek 3 , 91.Xr getc 3 , 92.Xr setvbuf 3 93.Sh STANDARDS 94The 95.Fn ungetc 96function conforms to 97.St -isoC . 98