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.\" 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 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 getc 3 , 89.Xr fseek 3 , 90.Xr setvbuf 3 91.Sh STANDARDS 92The 93.Fn ungetc 94function conforms to 95.St -ansiC . 96