返回子类型的成员模板函数

Question

是否有一种为模板类定义成员函数的正确方法，该模板类返回子类的实例？

下面是不VC++编译2010为例：

template<class T> class A { 
public: 
    class B { 
    public: 
     T i; 
    }; 

    A(); 
    B* foo(); 
}; 

///////////////////////////////////////////// 

template<class T> A<T>::A() {} 

template<class T> A<T>::B* A<T>::foo() { 
    cout << "foo" << endl; 
    return new B(); 
} 

我得到

Error 8 error C1903: unable to recover from previous error(s); stopping compilation 

在该行的定义foo的的开始。

我有正确的夹杂物和名称空间声明iostream等

谢谢你们！

编辑：

按照要求，这里是错误的完整列表，所有在同一行：

Warning 1 warning C4346: 'A<T>::B' : dependent name is not a type 
Error 2 error C2143: syntax error : missing ';' before '*' 
Error 3 error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 
Error 4 error C1903: unable to recover from previous error(s); stopping compilation 
Warning 5 warning C4346: 'A<T>::B' : dependent name is not a type 
Error 6 error C2143: syntax error : missing ';' before '*' 
Error 7 error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 
Error 8 error C1903: unable to recover from previous error(s); stopping compilation 

Answer 1

名称A<T>::B是depedent，你需要在暗示depedented名字是编译器键入

template<class T> typename A<T>::B* A<T>::foo() {...}

同为这一行： return new B(); - >return new typename A<T>::B();

阅读：Where and why do I have to put the "template" and "typename" keywords?