Static member functions error; How to properly write the signature?

问题

I am getting an error when trying to compile my code in g++ using the current signature:

cannot declare member function static void Foo::Bar(std::ostream&, const Foo::Node*) to have static linkage

My question is twofold:

1. Why does it not Compile this way?
2. What is the correct signature, and why?

Signatures have always been the death of me when using C++

Edit: Here is the class header file, as well:

class Foo {


public:
    Foo();

    ~Foo();

    bool insert(const Foo2 &v);

    Foo * find(const Foo2 &v);

    const Foo * find(const Foo2 &v) const;

    void output(ostream &s) const;

private:
    //Foo(const Foo &v);
    //Foo& operator =(const Foo &v);
    //Not implemented; unneeded


    struct Node {
        Foo2 info;
        Node *left;
        Node *right;
    };

    Node * root;

    static bool insert(const Foo2 &v, Node *&p);


    static void output(ostream &s, const Node *p);


    static void deleteAll(Node *p);

回答1:

I'm guessing you've done something like:

class Foo
{
    static void Bar();
};

...

static void Foo::Bar()
{
    ...
}

The "static void Foo::Bar" is incorrect. You don't need the second "static".

来源：https://stackoverflow.com/questions/8130066/static-member-functions-error-how-to-properly-write-the-signature