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.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)ungetc.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd June 4, 1993 36.Dt UNGETC 3 37.Os 38.Sh NAME 39.Nm ungetc 40.Nd un-get character from input stream 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In stdio.h 45.Ft int 46.Fn ungetc "int c" "FILE *stream" 47.Sh DESCRIPTION 48The 49.Fn ungetc 50function pushes the character 51.Fa c 52(converted to an unsigned char) 53back onto the input stream pointed to by 54.Fa stream . 55The pushed-back characters will be returned by subsequent reads on the 56stream (in reverse order). 57A successful intervening call, 58using the same stream, 59to one of the file positioning functions 60.Xr ( fseek 3 , 61.Xr fsetpos 3 , 62or 63.Xr rewind 3 ) 64will discard the pushed back characters. 65.Pp 66One character of push-back is guaranteed, 67but as long as there is sufficient memory, 68an effectively infinite amount of pushback is allowed. 69.Pp 70If a character is successfully pushed-back, 71the end-of-file indicator for the stream is cleared. 72The file-position indicator is decremented 73by each successful call to 74.Fn ungetc ; 75if its value was 0 before a call, its value is unspecified after 76the call. 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.Xr ungetwc 3 94.Sh STANDARDS 95The 96.Fn ungetc 97function conforms to 98.St -isoC . 99