class Fruit { public: void peel(); slice(); juice();
int operator+(Fruit &f); // overload "+"
operator
private: int weight, calories_per_oz;
} ;
Then provide a body for the overloaded operator function:
int Fruit::operator+(Fruit &f) {
printf("calling fruit addition\n"); // just so we
can see
return weight + f.weight;
}
As before, every method is passed an implicit this pointer, allowing us to reference the left operand
of the operator. The right operand of the addition is the parameter called f here; it is an instance of
Fruit, and the preceding ampersand indicates it is passed by reference.
The overloaded function can be called like this:
Apple apple;
Fruit orange;
int ounces = apple+orange;
The precedence and number of operands ("arity" in compiler jargon) remain the same for the
overloaded operator as for the original operator. So, you see, C++ says you can add apples to oranges,
if you define it first. C++ gives the phrase "operator error" a whole new class of meanings.
Overloading is also very convenient in C++ I/O, described in the next section.
Input/Output in C++
As well as having the stdio library of C, C++ features some new I/O routines and concepts of its own.
There is an I/O interface known as iostream.h that helps to make I/O more convenient [3] and more
in tune with the object-oriented philosophy.
[3] Don't confuse the C++ iostream (formerly known as streams) I/O interface with the
unrelated UNIX kernel STREAMS framework for communicating between a device driver and a
user process.
The operators << (to put, or "insert") and >> (to get, or "extract") are used instead of functions like
putchar() and getchar().