Delegating Constructors

If you provide a class with several constructors, you may find yourself writing the same code over and over. That is, some of the constructors may require you to duplicate code already present in other constructors. To make coding simpler and more reliable, C++11 allows to you use a constructor as part of the definition of another constructor. This process is termed delegation because one constructor temporarily delegates responsibility to another constructor to work on the object it is constructing. Delegation uses a variant of the member initialization list syntax:

class Notes {
    int k;
    double x;
    std::string st;
public:
    Notes();
    Notes(int);
    Notes(int, double);
    Notes(int, double, std::string);
};
Notes::Notes(int kk, double xx, std::string stt) : k(kk),
             x(xx), st(stt) {/*do stuff*/}
Notes::Notes() : Notes(0, 0.01, "Oh") {/* do other stuff*/}
Notes::Notes(int kk) : Notes(kk, 0.01, "Ah") {/* do yet other stuff*/ }
Notes::Notes( int kk, double xx ) : Notes(kk, xx, "Uh") {/* ditto*/ }

The default constructor, for example, uses the first constructor in the list to initialize the data members and to also do whatever the body of that constructor requests. Then it finishes up doing whatever its own body requests.