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.\" $FreeBSD$ 35.Dd October 17, 2000 36.Os 37.Dt FMTCHECK 3 38.Sh NAME 39.Nm fmtcheck 40.Nd sanitizes user-supplied printf(3)-style format string 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.Fd #include <stdio.h> 45.Ft const char * 46.Fn fmtcheck "const char *fmt_suspect" "const char *fmt_default" 47.Sh DESCRIPTION 48The 49.Fn fmtcheck 50scans 51.Fa fmt_suspect 52and 53.Fa fmt_default 54to determine if 55.Fa fmt_suspect 56will consume the same argument types as 57.Fa fmt_default 58and to ensure that 59.Fa fmt_suspect 60is a valid format string. 61.Pp 62The 63.Xr printf 3 64family of functions can not verify the types of arguments that they are 65passed at run-time. In some cases, like 66.Xr catgets 3 , 67it is useful or necessary to use a user-supplied format string with no 68guarantee that the format string matches the specified parameters. 69.Pp 70The 71.Fn fmtcheck 72was designed to be used in these cases, as in: 73.Bd -literal -offset indent 74printf(fmtcheck(user_format, standard_format), arg1, arg2); 75.Ed 76.Pp 77In the check, field widths, fillers, precisions, etc. are ignored (unless 78the field width or precision is an asterisk 79.Ql * 80instead of a digit string). Also, any text other than the format specifiers 81is completely ignored. 82.Pp 83Note that the formats may be quite different as long as they accept the 84same parameters. For example, 85.Qq Li "%p %o %30s %#llx %-10.*e %n" 86is compatible with 87.Qq Li "This number %lu %d%% and string %s has %qd numbers and %.*g floats (%n)" . 88However, 89.Qq Li %o 90is not equivalent to 91.Qq Li %lx 92because 93the first requires an integer and the second requires a long. 94.Sh RETURN VALUES 95If 96.Fa fmt_suspect 97is a valid format and consumes the same argument types as 98.Fa fmt_default , 99then the 100.Fn fmtcheck 101will return 102.Fa fmt_suspect . 103Otherwise, it will return 104.Fa fmt_default . 105.Sh SEE ALSO 106.Xr printf 3 107