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fmtcheck(3) [osx man page]

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

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. 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. SEE ALSO
printf(3) BUGS
The fmtcheck() function does not recognize positional parameters. BSD
October 16, 2002 BSD

Check Out this Related Man Page

vprintf(3int)															     vprintf(3int)

       vprintf, vfprintf, vsprintf - print formatted output of a varargs argument list

       #include <stdio.h>
       #include <varargs.h>

       int vprintf ( format, ap )
       char *format;
       va list ap;

       int vfprintf ( stream, format, ap )
       FILE *stream;
       char *format;
       va list ap;

       int vsprintf ( s, format, ap )
       char *s, *format;
       va list ap;

       The international functions and are similar to the standard I/O functions.

       Likewise,  the  vprintf functions are similar to the printf functions except they are called with an argument list as defined by instead of
       with a variable number of arguments.

       The international functions allow you to use the %digit$ conversion character in place of the % character  you  use  in	the  standard  I/O
       functions.   The digit is a decimal digit n from 1 to 9.  The international functions apply conversions to the nth argument in the argument
       list, rather than to the next unused argument.

       You can use the % conversion character in the international functions.  However, you cannot mix the % conversion character with the %digit$
       conversion character in a single call.

       You  can  indicate  a  field  width or precision by an asterisk (*) instead of a digit string in format strings containing the % conversion
       character. If you use an asterisk, you can supply an integer arg that specifies the field width or precision.  In format strings containing
       the  %digit$  conversion character, you can indicate field width or precision by the sequence *digit$.  You use a decimal digit from 1 to 9
       to indicate which argument contains an integer that specifies the field width or precision.

       The conversion characters and their meanings are identical to

       You must use each digit argument at least once.

       #include <stdio.h>
       #include <varargs.h>

       char *function_name = "vpr";
       char *arg1 = "hello world";
       int arg2 = 2;
       char *arg3 = "study";

       char *i18nfmt = "%1$s %3$d

       test(function_name, i18nfmt, arg1, arg2, arg3);

       va_list args;
       char *fmt;
       char string[1024];


       (void)printf("function %s: ", va_arg(args, char *));

       fmt = va_arg(args, char *);

       (void)vprintf(fmt, args);


See Also
       setlocale(3), scanf(3int), printf(3s), printf(3int), vprintf(3s), putc(3s), scanf(3s), stdio(3s), varargs(3)
       Guide to Developing International Software

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