在内部类中使用struct时发生编译错误

Question

I could not find any answer that helped me understand why the following code does not compile. Im declaring a struct within the private part of a class (Foo), and trying to use it from within an inner class (Bar) like this.

class Foo {
public:
    Foo();
    class Bar;

    class Bar {
    public:
        Bar();
        Foo::Node createNode();
    };

private:
     struct Node{
        Node(int d) : data(d) {};
        int data;
     };
};

And the compiler throws the following error:

.../Foo.h:9:14: error: no type named 'Node' in 'Foo'

Answer 1

You need to declare the inner class before referencing it:

class Foo {
    class Node;
public:

    // ...