Same class as a member inside a class in C++?

Sorry I ill formed the question earlier. The piece of code is something like:

class Bar
{
    public:
        // some stuff

    private:
        struct Foo
        {
            std::unordered_map<std::string, std::unique_ptr<Foo>> subFoo;
            // some other basic variables here
        };

        Foo foo;
};

I got the basic idea about subFoo. But I am wondering that a single instance of Bar will contain only a single instance of Foo that is foo member variable? So a single instance/object of Bar will not be able to map multiple Foo inside the subFoo?

It feels like I am missing something here, can anyone break it down for me?

>Solution :

There are more misunderstandings about nested class definitions than there are actual benefits. In your code it really does not matter much and we can change it to:

struct Foo {
    std::unordered_map<std::string, std::unique_ptr<Foo>> subFoo;
    // some other basic variables here
};

class Bar
{
        Foo foo;
};

Foo is now defined in a different scope and it is no longer private to Bar. Otherwise it makes no difference for the present code.

I am wondering that a single instance of Bar will contain only a single instance of Foo that is foo member variable?

Yes.

So a single instance/object of Bar will not be able to map multiple Foo inside the subFoo?

subFoo is a map holding unique pointers to Foos. Bar::foo is not managed by a unique pointer, hence placing them in subFoo is not possible without running into a double free error. std::unique_ptr can be used with a custom deleter, but thats not the case here. Hence you cannot store a unique pointer to Bar::foo in any Foo::subFoo. You can however, store unique pointers to other Foos in Foo::subFoo.