C++: << for Your Classes
The << operator is defined for standard C++ types, like
int, float, etc.
When you create your own class you typically need to redefine
<< to output objects of that class.
This is possible in C++ thanks to overloading, which allows the same
function/operator to be defined for different types of data.
As the object to be output is the righthand operand of <<
it cannot be a member function of your class (it's a C++ restriction that
it must be the lefthand operand in order to overload the operator as a
member function).
At the same time your overloaded operator typically needs to access the
private data in your object.
Therefore the overloaded operator has to be declared as a friend
of your class.
To do this, in your class header file before any public or
private parts, declare the overloaded operator like this:
friend ostream &operator <<(ostream &OutputStream,const YourClassName &TheObject);
and in the implementation file for the class you implement the overloaded
operator something like this:
ostream &operator <<(ostream &OutputStream,const YourClassName &TheObject) {
OutputStream << TheObject.PrivateData;
return(OutputStream);
}
Of course your implementation can do more than simply output the
private data.