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.\" 34.\" $FreeBSD: src/lib/libc/gen/fmtcheck.3,v 1.10 2008/08/02 06:02:42 das Exp $ 35.\" $DragonFly: src/lib/libc/gen/fmtcheck.3,v 1.2 2003/06/17 04:26:42 dillon Exp $ 36.Dd October 16, 2002 37.Os 38.Dt FMTCHECK 3 39.Sh NAME 40.Nm fmtcheck 41.Nd sanitizes user-supplied 42.Xr printf 3 Ns -style 43format string 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In stdio.h 48.Ft const char * 49.Fn fmtcheck "const char *fmt_suspect" "const char *fmt_default" 50.Sh DESCRIPTION 51The 52.Fn fmtcheck 53scans 54.Fa fmt_suspect 55and 56.Fa fmt_default 57to determine if 58.Fa fmt_suspect 59will consume the same argument types as 60.Fa fmt_default 61and to ensure that 62.Fa fmt_suspect 63is a valid format string. 64.Pp 65The 66.Xr printf 3 67family of functions cannot verify the types of arguments that they are 68passed at run-time. 69In some cases, like 70.Xr catgets 3 , 71it is useful or necessary to use a user-supplied format string with no 72guarantee that the format string matches the specified arguments. 73.Pp 74The 75.Fn fmtcheck 76was designed to be used in these cases, as in: 77.Bd -literal -offset indent 78printf(fmtcheck(user_format, standard_format), arg1, arg2); 79.Ed 80.Pp 81In the check, field widths, fillers, precisions, etc.\& are ignored (unless 82the field width or precision is an asterisk 83.Ql * 84instead of a digit string). 85Also, any text other than the format specifiers 86is completely ignored. 87.Sh RETURN VALUES 88If 89.Fa fmt_suspect 90is a valid format and consumes the same argument types as 91.Fa fmt_default , 92then the 93.Fn fmtcheck 94will return 95.Fa fmt_suspect . 96Otherwise, it will return 97.Fa fmt_default . 98.Sh SECURITY CONSIDERATIONS 99Note that the formats may be quite different as long as they accept the 100same arguments. 101For example, 102.Qq Li "%p %o %30s %#llx %-10.*e %n" 103is compatible with 104.Qq Li "This number %lu %d%% and string %s has %qd numbers and %.*g floats (%n)" . 105However, 106.Qq Li %o 107is not equivalent to 108.Qq Li %lx 109because 110the first requires an integer and the second requires a long. 111.Sh SEE ALSO 112.Xr printf 3 113.Sh BUGS 114The 115.Fn fmtcheck 116function does not recognize positional parameters. 117