Consider following program.
#include <iostream>
using std::ostream;
using std::cout;
using std::istream;
using std::cin;
class three_d {
int i,j,k;
public:
three_d(int a,int b,int c) : i(a),j(b),k(c)
{ }
//friend ostream& operator << (ostream&,const three_d&);
//friend istream& operator >> (istream&,three_d&);
};
/*ostream& operator << (ostream& o,const three_d& t) {
o<<t.i<<", ";
o<<t.j<<", ";
o<<t.k<<"\n";
return o;
}
istream& operator >> (istream& stream,three_d &t) {
cout<<"Enter x,y,z values";
stream>>t.i>>t.j>>t.k;
return stream;
}*/
int main() {
three_d a(1,2,3),b(4,5,6),c(7,8,9);
cout<<a<<b<<c;
cin>>a;
cout<<a;
}
I've deliberately commented out the overloaded >> & << operator function definitions and compiler gives following error messages
*[Error] no match for 'operator<<' (operand types are 'std::ostream {aka std::basic_ostream<char>}' and 'three_d')
[Error] no match for 'operator>>' (operand types are 'std::istream {aka std::basic_istream<char>}' and 'three_d')*
By default even for empty class C++ compiler automatically provides following if programmer doesn't provide them.
1) Constructor
2) Destructor
3) Copy constructor
4) =(assigment) operator
Then why >> & << operators has to be explicitly overloaded by programmer to work with user defined types(class)? Wouldn't it be very nice if compiler by default provides overloaded >> & << operator functions for user defined types also? Doesn't that reduce the code required to write & reduces burden for the programmer?
