C++ Primer Plus

A Common Kind of Friend: Overloading the << Operator

One very useful feature of classes is that you can overload the << operator so that you can use it with cout to display an object’s contents. In some ways, this overloading is a bit trickier than the earlier examples, so we’ll develop it in two steps instead of in one.

Suppose trip is a Time object. To display Time values, we’ve been using Show(). Wouldn’t it be nice, however, if you could do the following?

cout << trip;  // make cout recognize Time class?

You can do this because << is one of the C++ operators that can be overloaded. In fact, it already is heavily overloaded. In its most basic incarnation, the << operator is one of C and C++’s bit manipulation operators; it shifts bits left ...