Annotation of src/lib/libc/gen/fmtcheck.3, Revision 1.8
1.8 ! apb 1: .\" $NetBSD: fmtcheck.3,v 1.7 2009/03/09 19:24:26 joerg Exp $
1.1 briggs 2: .\"
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1.8 ! apb 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.
1.8 ! apb 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
1.8 ! apb 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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