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.Dd June 4, 1993 33.Dt UNGETC 3 34.Os 35.Sh NAME 36.Nm ungetc 37.Nd un-get character from input stream 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In stdio.h 42.Ft int 43.Fn ungetc "int c" "FILE *stream" 44.Sh DESCRIPTION 45The 46.Fn ungetc 47function pushes the character 48.Fa c 49(converted to an unsigned char) 50back onto the input stream pointed to by 51.Fa stream . 52The pushed-back characters will be returned by subsequent reads on the 53stream (in reverse order). 54A successful intervening call, 55using the same stream, 56to one of the file positioning functions 57.Xr ( fseek 3 , 58.Xr fsetpos 3 , 59or 60.Xr rewind 3 ) 61will discard the pushed back characters. 62.Pp 63One character of push-back is guaranteed, 64but as long as there is sufficient memory, 65an effectively infinite amount of pushback is allowed. 66.Pp 67If a character is successfully pushed-back, 68the end-of-file indicator for the stream is cleared. 69The file-position indicator is decremented 70by each successful call to 71.Fn ungetc ; 72if its value was 0 before a call, its value is unspecified after 73the call. 74.Sh RETURN VALUES 75The 76.Fn ungetc 77function returns the character pushed-back after the conversion, 78or 79.Dv EOF 80if the operation fails. 81If the value of the argument 82.Fa c 83character equals 84.Dv EOF , 85the operation will fail and the stream will remain unchanged. 86.Sh SEE ALSO 87.Xr fseek 3 , 88.Xr getc 3 , 89.Xr setvbuf 3 , 90.Xr ungetwc 3 91.Sh STANDARDS 92The 93.Fn ungetc 94function conforms to 95.St -isoC . 96