Question

gcc 4.4.1

I am maintaining someone’s code and I have come across something that I don’t understand.

#define RES_API(name, func) name##_##func

Can anyone explain?

Many thanks,

Answer 1

The ## operator concatenates two tokens. In your case, name is appended with an underscore, and that is appended with func.

So RES_API(aName, aFunc) results in aName_aFunc.

By itself, it seems rather annoying. I could see a use when mixing C and C++ code, as C libraries tend to prefix their functions, while C++ libraries would place them in a namespace.

Given an alternate definition, such as:

#define RES_API(name, func) name##::##func

You suddenly have a generic way to switch between a C interface, or C++.