Error From Passing std::string Reference

Question

This is probably really simple and I'm just being an idiot.

When I try to compile (Linux, 64bit, gcc) this:

namespace GUI {

class Manager
{
...
    private:
        bool AddElement(const std::string&, Element*);

        /// Friend functions
        friend void Element::AddToManager(const std::string&);
};

class Element
{
...
    private:
        void AddToManager(const std::string&);
        Manager* mGuiManager;
...
}

void Element::AddToManager(const std::string& rName)
{
    mGuiManager->AddElement(rName, this); // Error on this line
}

}

I get the error:

undefined reference to `GUI::Manager::AddElement(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, GUI::Element*)'

Where should I start to resolve this?

Answer 1

我对错误中的STL位分心，而忘了我已经注释掉了实际功能。

Answer 2

您需要在Element类中添加以下声明：

friend class Manager;