Constructor for '' must explicitly initial

问题:

I have this class

class CamFeed {
public:
    // constructor
    CamFeed(ofVideoGrabber &cam); 
    ofVideoGrabber &cam;

};

And this constructor:

CamFeed::CamFeed(ofVideoGrabber &cam) {
    this->cam = cam;
}

I get this error on the constructor: Constructor for '' must explicitly initialize the reference member ''

What is a good way to get around this?

回答1:

You need to use the constructor initializer list:

CamFeed::CamFeed(ofVideoGrabber& cam) : cam(cam) {}

This is because references must refer to something and therefore cannot be default constructed. Once you are in the constructor body, all your data members have been initialized. Your this->cam = cam; line would really be an assignment, assigning the value referred to by cam to whatever this->cam refers to.