Union 2 arrays

Does anyone know any code to union 2 sets?

I have a prototype in my header file of:

Code:

IntegerSet& unionSet( IntegerSet& otherSet );

I want to union array c and b and am calling the function by:

Code:

c.unionSet( b );

What code could I use to combine into 1 array in the .cpp file, returning a reference to the array?

assuming it's an std::set, can't you use operator += ?

Or maybe the STL set_union function might be of use depending on how the storage of the data elements is implemented?