Passing parameters to printf()

I need to be able to pass parameters to printf from another function. What I have so far works for some data types, but not character buffers, aka strings. Here is what I have that does not work. The SetDirection() are for setting the data direction of external hardware.

int xprintf (char *fmt, ...) {
        int rv;
        register int *varg = (int *)(&fmt);
        SetDirection(1);
        rv = printf(fmt, varg);
        SetDirection(0);
        return rv;
}