MFC Programmer's SourceBook : Thinking in C++
Bruce Eckel's Thinking in C++, 2nd Ed Contents | Prev | Next

12:

Operator overloading

Operator overloading is just “syntactic sugar,” which means it is simply another way for you to make a function call.

The difference is the arguments for this function don’t appear inside parentheses, but instead surrounding or next to characters you’ve always thought of as immutable operators.

There are two differences between the use of an operator and an ordinary function call. The syntax is different; an operator is often “called” by placing it between or sometimes after the arguments. The second difference is that the compiler determines what “function” to call. For instance, if you are using the operator + with floating-point arguments, the compiler “calls” the function to perform floating-point addition (this “call” is typically the act of inserting in-line code, or a floating-point coprocessor instruction). If you use operator + with a floating-point number and an integer, the compiler “calls” a special function to turn the int into a float, and then “calls” the floating-point addition code.

But in C++, it’s possible to define new operators that work with classes. This definition is just like an ordinary function definition except the name of the function begins with the keyword operator and ends with the operator itself. That’s the only difference, and it becomes a function like any other function, which the compiler calls when it sees the appropriate pattern.

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