c++ - 如何设计将一个类放在另一个类名下

Question

有两个类foo和bar，bar为foo服务
我希望设计成
foo 与 foo::bar ， 而不是 foo 与 bar

类似
std::vector<int>::iterator 和 std::vector

应该怎样把bar的class放在foo里面？

Answer 1

You can use class nesting or typedef. The vector::iterator you mentioned is a type alias defined by typedef

class Out {
public:
    class Inside {
    
    };
};

Out some1;
Out::Inside some2;

class A {

};

class B {
public:
    typedef A Inside;
};

A some1;
B some2;
B::Inside some3;

Answer 2

C++ supports nested classes, such as

class foo {
    class bar { /* ... */ };
    /* ... */
};

or

class foo {
    class bar;
    /* ... */
};

class foo::bar {
    /* ... */
};

For specific usage, please refer to C++ Primer 5ed. section 19.5 Nested Classes.

In addition, std::vector<int>::iterator is an alias of another class in std::vector (typedef), not a nested class of std::vector.