/in/foo.cc: In function 'void output_A()':
/in/foo.cc:246:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
   printf("");
            ^
/in/foo.cc: In function 'void output_B()':
/in/foo.cc:266:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
   printf("");
            ^