c++ - Read an attribute of the base class using "istream" of derived class -


it looks coord(a) doesn't work , , values lon , lat 00.0000 , 00.0000, default constructor . should do? ia there problem syntax ? isn't in >> coord(a) read lon , lat base class?

 //base class class coord {     private:     double lon;     double lat; coord() { lon = 00.000000000000000; lat = 00.000000000000000; } //..... //..... //..... friend istream& operator>>(istream& in, coord& temp) {     cout << "longitude : "; in >> temp.lon;     cout << "latitude  : "; in >> temp.lat;     return in; } };  //derived class    class location : public coord { private:     char model[6];     double time;     int speed; //..... //..... //..... friend istream& operator>>(istream& in, location& a) {     cout << "model : "; in >> a.model;     cout << "time : "; in >> a.time;     cout << "speed : "; in >> a.speed;     cout << "coordinates : " << endl; in >> coord(a);     return in; } }; void main() {    location loc;    cin>>loc; cout<<loc; }

as said, coord(a) creates copy (much object slicing). code shouldn't compile, because you're passing rvalue operator>>, takes lvalue reference.

you have use static_cast, reference coord base class:

in >> static_cast<coord&>(a);

that make call right operator>>.


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