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.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 16.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 17.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 18.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 19.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 20.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 21.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 22.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 23.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 24.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 25.\" POSSIBILITY OF SUCH DAMAGE. 26.Dd October 16, 2002 27.Dt FMTCHECK 3 28.Os 29.Sh NAME 30.Nm fmtcheck 31.Nd sanitizes user-supplied 32.Xr printf 3 Ns -style 33format string 34.Sh LIBRARY 35.Lb libc 36.Sh SYNOPSIS 37.In stdio.h 38.Ft const char * 39.Fn fmtcheck "const char *fmt_suspect" "const char *fmt_default" 40.Sh DESCRIPTION 41The 42.Fn fmtcheck 43scans 44.Fa fmt_suspect 45and 46.Fa fmt_default 47to determine if 48.Fa fmt_suspect 49will consume the same argument types as 50.Fa fmt_default 51and to ensure that 52.Fa fmt_suspect 53is a valid format string. 54.Pp 55The 56.Xr printf 3 57family of functions cannot verify the types of arguments that they are 58passed at run-time. 59In some cases, like 60.Xr catgets 3 , 61it is useful or necessary to use a user-supplied format string with no 62guarantee that the format string matches the specified arguments. 63.Pp 64The 65.Fn fmtcheck 66was designed to be used in these cases, as in: 67.Bd -literal -offset indent 68printf(fmtcheck(user_format, standard_format), arg1, arg2); 69.Ed 70.Pp 71In the check, field widths, fillers, precisions, etc.\& are ignored (unless 72the field width or precision is an asterisk 73.Ql * 74instead of a digit string). 75Also, any text other than the format specifiers 76is completely ignored. 77.Sh RETURN VALUES 78If 79.Fa fmt_suspect 80is a valid format and consumes the same argument types as 81.Fa fmt_default , 82then the 83.Fn fmtcheck 84will return 85.Fa fmt_suspect . 86Otherwise, it will return 87.Fa fmt_default . 88.Sh SEE ALSO 89.Xr printf 3 90.Sh BUGS 91The 92.Fn fmtcheck 93function does not recognize positional parameters. 94.Sh SECURITY CONSIDERATIONS 95Note that the formats may be quite different as long as they accept the 96same arguments. 97For example, 98.Qq Li "%p %o %30s %#llx %-10.*e %n" 99is compatible with 100.Qq Li "This number %lu %d%% and string %s has %qd numbers and %.*g floats (%n)" . 101However, 102.Qq Li %o 103is not equivalent to 104.Qq Li %lx 105because 106the first requires an integer and the second requires a long. 107