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[dragonfly.git] / lib / libc / stdio / ungetc.3
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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.
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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
e0f95098 33.\" $FreeBSD: src/lib/libc/stdio/ungetc.3,v 1.14 2007/01/09 00:28:07 imp Exp $
1de703da 34.\" $DragonFly: src/lib/libc/stdio/ungetc.3,v 1.2 2003/06/17 04:26:46 dillon Exp $
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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.
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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.
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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 ,
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93.Xr setvbuf 3 ,
94.Xr ungetwc 3
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95.Sh STANDARDS
96The
97.Fn ungetc
98function conforms to
99.St -isoC .