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Asked: 2026-06-12T09:07:30+00:00

I have seen this question: How to generate random variable names in C++ using

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I have seen this question:

How to generate random variable names in C++ using macros?

with the following answer: https://stackoverflow.com/a/1675203/551045

And I’ve tried to implement it in clang.

Here is my declaration:

#define TRACE(stream) FuncTrace x#__COUNTER__ (llvm::errs(), "hallo", 1)

I tried all variations x##__COUNTER__; x ## __COUNTER__ and so on but none seem to work.

Could this be a clang bug? The clang help page says it has the __COUNTER__ macro.

In the end the macro I need something like this:

#define TRACE(stream) FuncTrace x#__COUNTER__ (stream, __FUNCTION__, __LINE__)
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1 Answer

  1. Editorial Team

    1. To concatenate two tokens into one you use the ## operator. The # operator is used to turn a token into a string.

    2. x ## __COUNTER__ will just produce x__COUNTER__. You need to fully expand __COUNTER__ first. One possible method is add a few more indirections, e.g.

      #define YTRACE(x, y) FuncTrace x##y (llvm::errs(), __FUNCTION__, __LINE__)
#define XTRACE(x, y) YTRACE(x, y)
#define TRACE(x) XTRACE(x, __COUNTER__)
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