iOS - how do I check if a string is numeric or not?

Possible Duplicate:
iPhone how to check that a string is numeric only

I am trying to look up some basic functionality in Objective C, but can't seem to locate the basic answer.

What I really need is to check

if ( some_string is numeric )
{

}

I would assume there would just be some built in function for that. No?

I am looking at this StackOverflow question How to check if NSString is numeric or not and they seem to be doing things the very complicated way.

Isn't there some basic check I can do in one simple line?

Thanks!