HowToGetTheNameOfCallEpxr

Dear all,
I am interested in how to get the name of function-call.
Here is an example:
i = sin(x); //the right part is an statement whose class is CallExprClass.
Now I want to get the name of the CallExpr, namely:“sin”.
Could you tell me how to get the name?

/cheers.
By Redder.