modernc.org/cc@v1.0.1/v2/testdata/cpp-expand/example-6.10.3.3-4.h (about)

     1  #define hash_hash # ## #
     2  #define mkstr(a) # a
     3  #define in_between(a) mkstr(a)
     4  #define join(c, d) in_between(c hash_hash d)
     5  char p[] = join(x, y); // equivalent to
     6                         // char p[] = "x ## y";