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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 guaran-
     tee 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.	Otherwise, it
     will return fmt_default.

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 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	re-
     quires an integer and the second requires a long.

SEE ALSO
     printf(3)

BUGS
     The fmtcheck() function does not recognize	positional parameters.

BSD			       October 16, 2002				   BSD

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | SECURITY CONSIDERATIONS | SEE ALSO | BUGS

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