为什么我们把别的东西放在宏的最后

Question

  

可能重复：
  Why are there sometimes meaningless do/while and if/else statements in C/C++ macros?

#define QL_REQUIRE(condition,message) \
if (!(condition)) { \
    std::ostringstream _ql_msg_stream; \
    _ql_msg_stream << message; \
    throw QuantLib::Error(__FILE__,__LINE__, \
                          BOOST_CURRENT_FUNCTION,_ql_msg_stream.str()); \
 } else 

如何使用它：

void testingMacros1 (){
   double x =0.0;
   QL_REQUIRE (x!=0 ," Zero number !");
}

为什么宏最终会注入else？