FMTCHECK(3)						   BSD Library Functions Manual 					       FMTCHECK(3)

NAME

     fmtcheck -- sanitizes user-supplied printf(3)-style format string

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <stdio.h>

     const char *
     fmtcheck(const char *fmt_suspect, const char *fmt_default);

DESCRIPTION

     The fmtcheck() scans 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 cannot 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 arguments.

     The fmtcheck() 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.

RETURN VALUES

     If fmt_suspect is a valid format and consumes the same argument types as fmt_default, then the fmtcheck() will return fmt_suspect.  Other-
     wise, it will return fmt_default.

SEE ALSO

     printf(3)

BUGS

     The fmtcheck() function does not recognize positional parameters.

SECURITY CONSIDERATIONS

     Note that the formats may be quite different as long as they accept the same arguments.  For example, "%p %o %30s %#llx %-10.*e %n" is com-
     patible 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.

BSD
								 October 16, 2002							       BSD