Unexpected predefined macro behaviour when pasting tokens

Question

The following (test with gcc -E blah.c):

#define UNUSED(type) type UNUSED_ ## __COUNTER__
UNUSED(char const *)
UNUSED(int)

Generat

Answer 1

I believe you must "double expand" it:

#define STR(x)    #x
#define UNUSED(type) type UNUSED_ ## STR(__COUNTER__)
UNUSED(char const *) 
UNUSED(int)