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FMTCHECK(3) DragonFly 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
 requires an integer and the second requires a long.
SEE ALSO
 printf(3)
BUGS
 The fmtcheck() function does not recognize positional parameters.
DragonFly 3.5 October 16, 2002 DragonFly 3.5

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