Overload function on parent and child - how to access the parent function

Here is what I would like to do:

class Msg {
    int target;
public:
    Msg(int target): target(target) { }
    virtual ~Msg () { }
    virtual MsgType GetType()=0;
};

inline std::ostream& operator <<(std::ostream& ss,Msg const& in) {
    return ss << "Target " << in.target;
}

class Greeting : public Msg {
    std::string text;
public:
    Greeting(int target,std::string const& text) : Msg(target),text(text);
    MsgType GetType() { return TypeGreeting; }
};

inline std::ostream& operator <<(std::ostream& ss,Greeting const& in) {
    return ss << (Msg)in << " Text " << in.text;
}开发者_StackOverflow社区

Unfortunately, this doesn't work as the cast to Msg on the second last line fails as Msg is abstract. I would however like to have the code to output the information for the parent in only one place. What is the correct way to do this? Thanks!

EDIT: Sorry, just to be clear, it is this line return ss << (Msg)in << " Text " << in.text; I don't know how to write.

Try ss<<(Msg const&)in. And probably you have to make operator a friend of Greeting class.

#include "iostream"
#include "string"

typedef enum {  TypeGreeting} MsgType;

class Msg {
    friend inline std::ostream& operator <<(std::ostream& ss,Msg const& in);

    int target;
public:
    Msg(int target): target(target) { }
    virtual ~Msg () { };
        virtual MsgType GetType()=0;
};

inline std::ostream& operator <<(std::ostream& ss,Msg const& in) {
    return ss << "Target " << in.target;
}

class Greeting : public Msg {
    friend inline std::ostream& operator <<(std::ostream& ss,Greeting const& in);

    std::string text;
public:
    Greeting(int target,std::string const& text) : Msg(target),text(text) {};
    MsgType GetType() { return TypeGreeting; }

};

inline std::ostream& operator <<(std::ostream& ss,Greeting const& in) {
    return ss << (Msg const&)in << " Text " << in.text;
}

int _tmain(int argc, _TCHAR* argv[])
{
    Greeting grt(1,"HELLZ");
    std::cout << grt << std::endl;
    return 0;
}

Not great design, but solves your problem.