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. 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.\" 34.Dd June 4, 1993 35.Dt UNGETC 3 36.Os 37.Sh NAME 38.Nm ungetc 39.Nd un-get character from input stream 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In stdio.h 44.Ft int 45.Fn ungetc "int c" "FILE *stream" 46.Sh DESCRIPTION 47The 48.Fn ungetc 49function pushes the character 50.Fa c 51(converted to an unsigned char) 52back onto the input stream pointed to by 53.Fa stream . 54The pushed-back characters will be returned by subsequent reads on the 55stream (in reverse order). 56A successful intervening call, 57using the same stream, 58to one of the file positioning functions 59.Xr ( fseek 3 , 60.Xr fsetpos 3 , 61or 62.Xr rewind 3 ) 63will discard the pushed back characters. 64.Pp 65One character of push-back is guaranteed, 66but as long as there is sufficient memory, 67an effectively infinite amount of pushback is allowed. 68.Pp 69If a character is successfully pushed-back, 70the end-of-file indicator for the stream is cleared. 71The file-position indicator is decremented 72by each successful call to 73.Fn ungetc ; 74if its value was 0 before a call, its value is unspecified after 75the call. 76.Sh RETURN VALUES 77The 78.Fn ungetc 79function returns the character pushed-back after the conversion, 80or 81.Dv EOF 82if the operation fails. 83If the value of the argument 84.Fa c 85character equals 86.Dv EOF , 87the operation will fail and the stream will remain unchanged. 88.Sh SEE ALSO 89.Xr fseek 3 , 90.Xr getc 3 , 91.Xr setvbuf 3 , 92.Xr ungetwc 3 93.Sh STANDARDS 94The 95.Fn ungetc 96function conforms to 97.St -isoC . 98