/in/foo.cc: In function 'void output_A()':
/in/foo.cc:239:18: warning: zero-length gnu_printf format string [-Wformat-zero-length]
         printf("");
                  ^
/in/foo.cc: In function 'void output_B()':
/in/foo.cc:259:18: warning: zero-length gnu_printf format string [-Wformat-zero-length]
         printf("");
                  ^