CODEWITHSUNDEEP
cmacros
Sam Martens
Sam Martens

Reputation: 61

Make token concatenation before stringification in C macro

I have two C macros, the first one is basically concatenating two tokens

#define _PY_CLASS_NAME(name) Py##name

The second macro is stringifying input argument 

#define STR(text) #text

Because of the way C preprocessor work when I try something like

STR(_PY_CLASS_NAME(name))

I actually get "_PY_CLASS_NAME(name)". So the question is, how to avoid it?

I tried something like

#define CONCAT(A, B) #A###B

and it works. But maybe it is a better way to do it?

Upvotes: 0

Views: 297

Answers (1)

user2736738
user2736738

Reputation: 30926

#define _PY_CLASS_NAME(name) Py##name
#define STR(a) STR_(a)
#define STR_(a) #a

This solves the problem in a different way and also would clarify how it macro works. Reason is - when macro arguments are substituted in the macro body, they are expanded until they appear with the # or ## pre-processor operators in that macro.

Now doing this printf("%s\n",STR(_PY_CLASS_NAME(name))); prints Pyname.

Edit: The second one you mentioned won't work. The compiler complains as mentioned, of absence of valid preprocessing token.

Upvotes: 1

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