|File: [cvs.NetBSD.org] / src / lib / libc / gen / fmtcheck.3 (download)
Revision 126.96.36.199, Wed Aug 20 00:02:14 2014 UTC (4 years, 5 months ago) by tls
Changes since 1.7: +6 -4
Rebase to HEAD as of a few days ago.
.\" $NetBSD: fmtcheck.3,v 188.8.131.52 2014/08/20 00:02:14 tls Exp $
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.Dd June 14, 2014
.Dt FMTCHECK 3
.Nd sanitizes user-supplied printf(3)-style format string
.Ft const char *
.Fn fmtcheck "const char *fmt_suspect" "const char *fmt_default"
to determine if
will consume the same argument types as
and to ensure that
is a valid format string.
.Xr printf 3
family of functions can not verify the types of arguments that they are
passed at run-time.
In some cases, like
.Xr catgets 3 ,
it is useful or necessary to use a user-supplied format string with no
guarantee that the format string matches the specified parameters.
function was designed to be used in these cases, as in:
.Bd -literal -offset indent
printf(fmtcheck(user_format, standard_format), arg1, arg2);
In the check, field widths, fillers, precisions, etc. are ignored (unless
the field width or precision is an asterisk
instead of a digit string).
Also, any text other than the format specifiers is completely ignored.
Note that the formats may be quite different as long as they accept the
For example, "%ld %o %30s %#llx %-10.*e %n" is
compatible with "This number %lu %d%% and string %s has %qd numbers
and %.*g floats (%n)."
However, "%o" is not equivalent to "%lx" because
the first requires an integer and the second requires a long,
and "%p" is not equivalent to "%lu" because
the first requires a pointer and the second requires a long.
.Sh RETURN VALUES
is a valid format and consumes the same argument types as
.Fa fmt_default ,
function will return
.Fa fmt_suspect .
Otherwise, it will return
.Fa fmt_default .
.Sh SEE ALSO
.Xr printf 3