Question

I am using two classes in my C++ application. The code is as follows:

class MyMessageBox
{
public:
    void sendMessage(Message *msg, User *recvr);
    Message receiveMessage();
    list<Message> dataMessageList;
};

class User
{
public:
    MyMessageBox *dataMsgBox;
};

The msg is a pointer to a derived class object of Message class. I have implemented the function sendMessage as follows:

void MyMessageBox::sendMessage(Message *msg, User *recvr)
{
    Message &msgRef = *msg;
    recvr->dataMsgBox->dataMessageList.push_back(msgRef);
}

When I compile this code, I get the following error:
undefined reference to `vtable for Message’. Please help me out to solve this issue.

Thanks,
Rakesh.

Answer 1

I don’t know what you’re trying to do with that msgRef, but it’s wrong. Are you an ex-Java programmer, by any chance?

If Message is a base class for derivatives of Message, you need to store pointers in the list. Change list<Message> to list<Message*>; and push_back(msgRef) should become push_back(msg), removing the msgRef code entirely.

Also, as a matter of style, it’s a bad idea to chain lots of -> operators together. It’s better to implement a method on User in this case that adds a Message to its own list and call that.