Calling Eclipse function from C++

Hi,

I have just started working with Elcipse and I have
got a problem which might rather be a primitive one. 

I need to have a function written in Eclipse, for
instance

*********************

concat_test(A, B):-
      concat_string([A, "_", B], X),
      writeln(X).

********************

And I want to call this function from a C++ program. I
gathered that I can call this function using 

post_goal(term(EC_functor("concat_test", 2), A, B));

But my problem is, how do I get the concat_test
function compiled? And what do I need to do if I want
to return the value of X from the concat_test
function?

Thanks in advance,
Sathish.

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