1.\" $NetBSD: ungetc.3,v 1.6 2002/02/07 07:00:27 ross 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.\" @(#)ungetc.3 8.1 (Berkeley) 6/4/93 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.Fd #include \*[Lt]stdio.h\*[Gt] 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-backed characters will be returned by subsequent reads on the 61stream (in reverse order). 62A successful intervening call, using the same stream, to one of the file 63positioning functions 64.Po 65.Xr fseek 3 , 66.Xr fsetpos 3 , 67or 68.Xr rewind 3 69.Pc 70will discard the pushed back characters. 71.Pp 72One character of push-back is guaranteed, 73but as long as there is 74sufficient memory, an effectively infinite amount of pushback is allowed. 75.Pp 76If a character is successfully pushed-back, 77the end-of-file indicator for the stream is cleared. 78.Sh RETURN VALUES 79The 80.Fn ungetc 81function 82returns 83the character pushed-back after the conversion, or 84.Dv EOF 85if the operation fails. 86If the value of the argument 87.Fa c 88character equals 89.Dv EOF , 90the operation will fail and the stream will remain unchanged. 91.Sh SEE ALSO 92.Xr fseek 3 , 93.Xr getc 3 , 94.Xr setvbuf 3 95.Sh STANDARDS 96The 97.Fn ungetc 98function conforms to 99.St -ansiC . 100