]> git.saurik.com Git - apple/libc.git/blame - gen/FreeBSD/fmtcheck.3
Libc-1439.100.3.tar.gz
[apple/libc.git] / gen / FreeBSD / fmtcheck.3
CommitLineData
5b2abdfb
A
1.\" Copyright (c) 2000 The NetBSD Foundation, Inc.
2.\" All rights reserved.
3.\"
4.\" This file was contributed to The NetBSD Foundation by Allen Briggs.
5.\"
6.\" Redistribution and use in source and binary forms, with or without
7.\" modification, are permitted provided that the following conditions
8.\" are met:
9.\" 1. Redistributions of source code must retain the above copyright
10.\" notice, this list of conditions and the following disclaimer.
11.\" 2. Redistributions in binary form must reproduce the above copyright
12.\" notice, this list of conditions and the following disclaimer in the
13.\" documentation and/or other materials provided with the distribution.
14.\" 3. All advertising materials mentioning features or use of this software
15.\" must display the following acknowledgement:
16.\" This product includes software developed by the NetBSD
17.\" Foundation, Inc. and its contributors.
18.\" 4. Neither the name of The NetBSD Foundation nor the names of its
19.\" contributors may be used to endorse or promote products derived
20.\" from this software without specific prior written permission.
21.\"
22.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
23.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
24.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
25.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
26.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
27.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
28.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
29.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
30.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
31.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
32.\" POSSIBILITY OF SUCH DAMAGE.
33.\"
1f2f436a 34.\" $FreeBSD: src/lib/libc/gen/fmtcheck.3,v 1.10 2008/08/02 06:02:42 das Exp $
9385eb3d 35.Dd October 16, 2002
5b2abdfb
A
36.Os
37.Dt FMTCHECK 3
38.Sh NAME
39.Nm fmtcheck
40.Nd sanitizes user-supplied
41.Xr printf 3 Ns -style
42format string
43.Sh LIBRARY
44.Lb libc
45.Sh SYNOPSIS
46.In stdio.h
47.Ft const char *
48.Fn fmtcheck "const char *fmt_suspect" "const char *fmt_default"
49.Sh DESCRIPTION
50The
51.Fn fmtcheck
52scans
53.Fa fmt_suspect
54and
55.Fa fmt_default
56to determine if
57.Fa fmt_suspect
58will consume the same argument types as
59.Fa fmt_default
60and to ensure that
61.Fa fmt_suspect
62is a valid format string.
63.Pp
64The
65.Xr printf 3
9385eb3d 66family of functions cannot verify the types of arguments that they are
3d9156a7
A
67passed at run-time.
68In some cases, like
5b2abdfb
A
69.Xr catgets 3 ,
70it is useful or necessary to use a user-supplied format string with no
9385eb3d 71guarantee that the format string matches the specified arguments.
5b2abdfb
A
72.Pp
73The
74.Fn fmtcheck
75was designed to be used in these cases, as in:
76.Bd -literal -offset indent
77printf(fmtcheck(user_format, standard_format), arg1, arg2);
78.Ed
79.Pp
3d9156a7 80In the check, field widths, fillers, precisions, etc.\& are ignored (unless
5b2abdfb
A
81the field width or precision is an asterisk
82.Ql *
3d9156a7
A
83instead of a digit string).
84Also, any text other than the format specifiers
5b2abdfb 85is completely ignored.
5b2abdfb
A
86.Sh RETURN VALUES
87If
88.Fa fmt_suspect
89is a valid format and consumes the same argument types as
90.Fa fmt_default ,
91then the
92.Fn fmtcheck
93will return
94.Fa fmt_suspect .
95Otherwise, it will return
96.Fa fmt_default .
9385eb3d
A
97.Sh SECURITY CONSIDERATIONS
98Note that the formats may be quite different as long as they accept the
3d9156a7
A
99same arguments.
100For example,
9385eb3d
A
101.Qq Li "%p %o %30s %#llx %-10.*e %n"
102is compatible with
103.Qq Li "This number %lu %d%% and string %s has %qd numbers and %.*g floats (%n)" .
104However,
105.Qq Li %o
106is not equivalent to
107.Qq Li %lx
108because
109the first requires an integer and the second requires a long.
5b2abdfb
A
110.Sh SEE ALSO
111.Xr printf 3
9385eb3d
A
112.Sh BUGS
113The
114.Fn fmtcheck
1f2f436a 115function does not recognize positional parameters.