/in/foo.cc: In function 'void output_A()':
/in/foo.cc:252:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
   printf("");
            ^
/in/foo.cc: In function 'void output_B()':
/in/foo.cc:272:12: warning: zero-length gnu_printf format string [-Wformat-zero-length]
   printf("");
            ^