isdigit() function

Hey,

I'm trying to use the isdigit() function on a character eg
string[position].isdigit()

but I don't know which class to #include for this to work.
Does anyone know which one I need to include? I've tried #include <string>, #include <cstdlib> and #include <locale> but it still says that it can't find the function isdigit().

Thanks,
Conor.

Unix man pages says its ctype.h

Thanks.

I am indeed an idiot though, it's
isdigit(string[position])
not
string[position.isdigit()].

I got too used to programmin in Eiffel.

Conor.