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NetBSD 6.1.5 - man page for fmtcheck (netbsd section 3)

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

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

     Standard C Library (libc, -lc)

     #include <stdio.h>

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

     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-sup-
     plied format string with no guarantee that the format string matches the specified parame-

     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 for-
     mat 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.

     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.


BSD					 October 17, 2000				      BSD
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