Preprocessor counter macro

Question

Is there a way to create a COUNTER() macro (which follows the C++11/14 standard) that is expanded to a number which increases by one every time COUNTER() is invoked?

I've thought about it, but couldn't find a way to make it work. I didn't find a way to store "state" in the COUNTER() macro.

Example:

#define COUNTER() <...> // Implementation goes here...
#define UNIQUE_NAME_1() TEST ## COUNTER()
#define UNIQUE_NAME_2() TEST ## COUNTER()

// Note how the COUNTER() macro can be used with other macros
// (it cannot be implemented with C++ code)

int main() {
    std::cout << STRINGIFY(UNIQUE_NAME_1()) << std::endl;
    std::cout << STRINGIFY(UNIQUE_NAME_2()) << std::endl;
}

Expected output:

TEST0 
TEST1

score 7 · Accepted Answer · answered Mar 11 '14 at 17:33

7

GCC, and (I believe) VC++ both provide the __COUNTER__ macro, which does about what you'd expect. I don't know that it follows the standard exactly, but it's probably close enough for real-world use.

answered Mar 11 '14 at 17:33

Michael Kohne

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2

http://stackoverflow.com/questions/652815/has-anyone-ever-had-a-use-for-the-counter-pre-processor-macro has some nice coverage on this topic. – mah Mar 11 '14 at 17:38

Preprocessor counter macro

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