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: src/lib/libc/stdio/ungetc.3,v 1.14 2007/01/09 00:28:07 imp Exp $ 34.\" $DragonFly: src/lib/libc/stdio/ungetc.3,v 1.2 2003/06/17 04:26:46 dillon Exp $ 35.\" 36.Dd June 4, 1993 37.Dt UNGETC 3 38.Os 39.Sh NAME 40.Nm ungetc 41.Nd un-get character from input stream 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In 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-back characters will be returned by subsequent reads on the 57stream (in reverse order). 58A successful intervening call, 59using the same stream, 60to one of the file positioning functions 61.Xr ( fseek 3 , 62.Xr fsetpos 3 , 63or 64.Xr rewind 3 ) 65will discard the pushed back characters. 66.Pp 67One character of push-back is guaranteed, 68but as long as there is sufficient memory, 69an effectively infinite amount of pushback is allowed. 70.Pp 71If a character is successfully pushed-back, 72the end-of-file indicator for the stream is cleared. 73The file-position indicator is decremented 74by each successful call to 75.Fn ungetc ; 76if its value was 0 before a call, its value is unspecified after 77the call. 78.Sh RETURN VALUES 79The 80.Fn ungetc 81function returns the character pushed-back after the conversion, 82or 83.Dv EOF 84if the operation fails. 85If the value of the argument 86.Fa c 87character equals 88.Dv EOF , 89the operation will fail and the stream will remain unchanged. 90.Sh SEE ALSO 91.Xr fseek 3 , 92.Xr getc 3 , 93.Xr setvbuf 3 , 94.Xr ungetwc 3 95.Sh STANDARDS 96The 97.Fn ungetc 98function conforms to 99.St -isoC . 100