foo.c: In function ‘main’:
foo.c:16:14: warning: zero-length gnu_printf format string [-Wformat-zero-length]
   16 |         Q(10,"");
      |              ^~
foo.c:2:30: note: in definition of macro ‘Q’
    2 | #define Q(A,B) case A:printf(B);break;
      |                              ^