compilers/pcc/pcc-1.0.0/cc/cpp/tests/test1

   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";