const
char
*
fmtcheck(
const char *fmt_suspect
, const char *fmt_default
)
fmt_suspect
and
fmt_default
to determine if
fmt_suspect
will consume the same argument types as
fmt_default
and to ensure that
fmt_suspect
is a valid format string.
The printf(3) family of functions can not verify the types of arguments that they are passed at run-time. In some cases, like 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.
The fmtcheck function was designed to be used in these cases, as in:
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 same parameters. For example, "%p %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.
fmt_suspect
is a valid format and consumes the same argument types as
fmt_default
,
then the
fmtcheck
function will return
fmt_suspect
.
Otherwise, it will return
fmt_default
.