NAME

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

LIBRARY

       Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS

       #include <stdio.h>
       (See libbsd(7) for include usage.)

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

DESCRIPTION

       The fmtcheck function 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 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,
       "%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.

RETURN VALUES

       If 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.

SEE ALSO

       printf(3)

Debian                                            June 14, 2014                                   fmtcheck(3bsd)