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Annotation of src/lib/libc/gen/fmtcheck.3, Revision 1.7.22.1

1.7.22.1! tls         1: .\"    $NetBSD: fmtcheck.3,v 1.8 2014/06/14 08:18:24 apb Exp $
1.1       briggs      2: .\"
                      3: .\" Copyright (c) 2000 The NetBSD Foundation, Inc.
                      4: .\" All rights reserved.
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                      6: .\" This file was contributed to The NetBSD Foundation by Allen Briggs.
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                      8: .\" Redistribution and use in source and binary forms, with or without
                      9: .\" modification, are permitted provided that the following conditions
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                     12: .\"    notice, this list of conditions and the following disclaimer.
                     13: .\" 2. Redistributions in binary form must reproduce the above copyright
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                     17: .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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1.7.22.1! tls        29: .Dd June 14, 2014
1.7       joerg      30: .Dt FMTCHECK 3
1.1       briggs     31: .Os
                     32: .Sh NAME
                     33: .Nm fmtcheck
                     34: .Nd sanitizes user-supplied printf(3)-style format string
                     35: .Sh LIBRARY
                     36: .Lb libc
                     37: .Sh SYNOPSIS
1.5       wiz        38: .In stdio.h
1.1       briggs     39: .Ft const char *
                     40: .Fn fmtcheck "const char *fmt_suspect" "const char *fmt_default"
                     41: .Sh DESCRIPTION
                     42: The
                     43: .Nm
                     44: function scans
                     45: .Fa fmt_suspect
                     46: and
                     47: .Fa fmt_default
                     48: to determine if
                     49: .Fa fmt_suspect
                     50: will consume the same argument types as
                     51: .Fa fmt_default
                     52: and to ensure that
                     53: .Fa fmt_suspect
                     54: is a valid format string.
                     55: .Pp
                     56: The
                     57: .Xr printf 3
                     58: family of functions can not verify the types of arguments that they are
1.3       wiz        59: passed at run-time.
                     60: In some cases, like
1.1       briggs     61: .Xr catgets 3 ,
                     62: it is useful or necessary to use a user-supplied format string with no
                     63: guarantee that the format string matches the specified parameters.
                     64: .Pp
                     65: The
                     66: .Nm
                     67: function was designed to be used in these cases, as in:
                     68: .Bd -literal -offset indent
                     69: printf(fmtcheck(user_format, standard_format), arg1, arg2);
                     70: .Ed
                     71: .Pp
                     72: In the check, field widths, fillers, precisions, etc. are ignored (unless
                     73: the field width or precision is an asterisk
                     74: .Ql *
1.3       wiz        75: instead of a digit string).
                     76: Also, any text other than the format specifiers is completely ignored.
1.1       briggs     77: .Pp
                     78: Note that the formats may be quite different as long as they accept the
1.3       wiz        79: same parameters.
1.7.22.1! tls        80: For example, "%ld %o %30s %#llx %-10.*e %n" is
1.1       briggs     81: compatible with "This number %lu %d%% and string %s has %qd numbers
1.3       wiz        82: and %.*g floats (%n)."
                     83: However, "%o" is not equivalent to "%lx" because
1.7.22.1! tls        84: the first requires an integer and the second requires a long,
        !            85: and "%p" is not equivalent to "%lu" because
        !            86: the first requires a pointer and the second requires a long.
1.1       briggs     87: .Sh RETURN VALUES
                     88: If
                     89: .Fa fmt_suspect
                     90: is a valid format and consumes the same argument types as
                     91: .Fa fmt_default ,
                     92: then the
                     93: .Nm
                     94: function will return
                     95: .Fa fmt_suspect .
                     96: Otherwise, it will return
                     97: .Fa fmt_default .
                     98: .Sh SEE ALSO
                     99: .Xr printf 3

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