C++ macro '##' doesn't work after '->' operator

Question

I have a shared_ptr object x, which has get and set methods as follows:

x->a_value();
x->set_a_value();
x->b_value();
x->set_b_value();
         


        

Answer 1

The preprocessor works on "tokens" - likes names and operators.

The ## operator creates a new token by pasting smaller parts together. In the first example set_##type##_value becomes set_a_value, which is a valid token.

In the second example ->##type##_value would become ->a_value, which is not a valid preprocessor token. It ought to be two tokens.

If you just make the line x->type##_value(); it should work. You get the separate tokens x, ->, a_value, (, ), and ;.