c++ - 成员函数声明中是否允许限定名称？

Question

这段代码被MSVC9.0接受。我的问题是根据标准(旧的和/或新的)它是否合法。也非常欢迎引用。

class X
{
   void X::f();
};

Answer 1

不，这是无效的。这里，X::f 是一个限定名；您正试图将其用作 declarator-id。 C++03 8.3[dcl.meaning]/1 列出了declarator-id 可能被限定的情况:

A declarator-id shall not be qualified except for

• the definition of a member function or static data member outside of its class,

• the definition or explicit instantiation of a function or variable member of a namespace outside of its namespace, or

• the definition of a previously declared explicit specialization outside of its namespace, or

• the declaration of a friend function that is a member of another class or namespace.

因为 X::f 不属于这四个类别中的任何一个，所以它是不正确的。

在C++03 9.3[class.mfct]/5中可以找到要求在类定义之外定义成员函数的规则:

If the definition of a member function is lexically outside its class definition, the member function name shall be qualified by its class name using the :: operator.