Custom printf/scanf suggestions desired

So far this is how I'm declaring my custom versions:

Code:

---

typedef struct _PAWBUF PAWSTR;
typedef struct _PAW_PUTF PAW_PUTF;
typedef struct _PAW_GETF PAW_GETF;

struct _PAW_PUTF
{
        pawzu        sizeof_ud;
        pawd        (*test)( void *ud, va_list va );
        pawd        (*take)( void *ud, PAWSTR *str );
        pawzu        (*size)( void *ud );
};

struct _PAW_GETF
{
        pawzu        sizeof_ud;
        pawd        (*test)( void *ud, va_list va );
        pawd        (*take)( void *ud, PAWSTR const *str );
};

/* Defaults used if NULL is given */
extern PAW_PUTF const *pawStdPutf;
extern PAW_GETF const *pawStdGetf;

PAW_API pawd        pawPutf( PAW_PUTF const *use, PAWSTR *str, paws format, ... );
PAW_API pawd        pawPutv
        ( PAW_PUTF const *use, PAWSTR *str, paws format, va_list va );

PAW_API pawd        pawGetf
        ( PAW_GETF const *use, PAWSTR const *str, paws format, ... );
PAW_API pawd        pawGetv
        ( PAW_GETF const *use, PAWSTR const *str, paws format, va_list va );

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Besides declaring externs for %s etc what suggestions does anyone have for more flexibility?

Judging by the lack of responses I'm guessing nobody has any suggestion for increasing flexibility so I'll just bulldoze ahead with this api