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.\" $FreeBSD$ 38.\" 39.Dd June 4, 1993 40.Dt UNGETC 3 41.Os 42.Sh NAME 43.Nm ungetc 44.Nd un-get character from input stream 45.Sh LIBRARY 46.Lb libc 47.Sh SYNOPSIS 48.Fd #include <stdio.h> 49.Ft int 50.Fn ungetc "int c" "FILE *stream" 51.Sh DESCRIPTION 52The 53.Fn ungetc 54function pushes the character 55.Fa c 56(converted to an unsigned char) 57back onto the input stream pointed to by 58.Fa stream . 59The pushed-back characters will be returned by subsequent reads on the 60stream (in reverse order). 61A successful intervening call, 62using the same stream, 63to one of the file positioning functions 64.Xr ( fseek 3 , 65.Xr fsetpos 3 , 66or 67.Xr rewind 3 ) 68will discard the pushed back characters. 69.Pp 70One character of push-back is guaranteed, 71but as long as there is sufficient memory, 72an effectively infinite amount of pushback is allowed. 73.Pp 74If a character is successfully pushed-back, 75the end-of-file indicator for the stream is cleared. 76The file-position indicator is decremented 77by each successful call to 78.Fn ungetc ; 79if its value was 0 before a call, its value is unspecified after 80the call. 81.Sh RETURN VALUES 82The 83.Fn ungetc 84function returns the character pushed-back after the conversion, 85or 86.Dv EOF 87if the operation fails. 88If the value of the argument 89.Fa c 90character equals 91.Dv EOF , 92the operation will fail and the stream will remain unchanged. 93.Sh SEE ALSO 94.Xr fseek 3 , 95.Xr getc 3 , 96.Xr setvbuf 3 97.Sh STANDARDS 98The 99.Fn ungetc 100function conforms to 101.St -isoC . 102