converting numeric to string in postgres code

Hi,
while hacking on some Postgres code I've found a problem.

I need to convert numeric to string. I've got datum with numeric inside, so
I'm getting it like:

Numeric *numeric = DatumGetNumeric(d);

but later I need to have string (most probably: const char *). I've found a
couple of different ways for doing that, but I'm not aware of side effects.

Which function/macro should I use?

thanks,
Szymon