Overloading the << Operator for Your Own Classes
The latest version of this topic can be found at Overloading the << Operator for Your Own Classes.
Output streams use the insertion (<<) operator for standard types. You can also overload the << operator for your own classes.
Example
The write function example showed the use of a Date structure. A date is an ideal candidate for a C++ class in which the data members (month, day, and year) are hidden from view. An output stream is the logical destination for displaying such a structure. This code displays a date using the cout object:
Date dt(1, 2, 92);
cout <<dt;
To get cout to accept a Date object after the insertion operator, overload the insertion operator to recognize an ostream object on the left and a Date on the right. The overloaded << operator function must then be declared as a friend of class Date so it can access the private data within a Date object.
// overload_date.cpp
// compile with: /EHsc
#include <iostream>
using namespace std;
class Date
{
int mo, da, yr;
public:
Date(int m, int d, int y)
{
mo = m; da = d; yr = y;
}
friend ostream& operator<<(ostream& os, const Date& dt);
};
ostream& operator<<(ostream& os, const Date& dt)
{
os << dt.mo << '/' << dt.da << '/' << dt.yr;
return os;
}
int main()
{
Date dt(5, 6, 92);
cout << dt;
}
5/6/92
Remarks
The overloaded operator returns a reference to the original ostream object, which means you can combine insertions:
cout <<"The date is" <<dt <<flush;