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

Michael Kohne · Accepted Answer · 2014-03-11 17:33:44Z

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, 2014 at 17:33

Michael Kohne

12.1k3 gold badges52 silver badges85 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

mah Over a year ago

stackoverflow.com/questions/652815/… has some nice coverage on this topic.

Collectives™ on Stack Overflow

Preprocessor counter macro

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related