How can I guarantee full macro expansion of a parameter before paste?

Question

I have a general macro:

#define mSwitch( Root, Case )  Root##_Case_##Case

#define mSpecialDisplay( what, Val )  mSwitch(mSpecialDisplay,what)(Val)
#define m         


        

Answer 1

This is the usual idiom for this:

#define mSwitch(Root, Case) mSwitch_(Root, Case)
#define mSwitch_(Root, Case) Root##_Case_##Case

All of the arguments to a C preprocessor macro are fully expanded before the macro itself is expanded, unless the # or ## operator is applied to them; then they're not expanded. So to get full expansion before ##, you pass the arguments through a wrapper macro that doesn't use ##.