8 - Operator overloading, Friends, and References.

Question 1

What is the relationship between operators and functions?

Answer 1

Operators are nothing but functions that are used with a slightly different syntax. We write x + 7 instead of +(x, 7). But the operator is a function that takes two arguments (often called operands in this case.)

Question 2

If operators basically are functions, why do they exist at all?

Answer 2

Operands are an example of what is often called syntactic sugar, meaning a slightly different syntax that people like.

Question 3

What is syntactic sugar?

Answer 3

Syntactic sugar us a syntax that people like. It may differ from the rest of the syntax.

Question 4

What is the syntax for the function declaration of an operator declaration?

Answer 4

An example is :

const Money operator + (const Money& amount1, const Money& amount 2);

Question 5

One major restriction on overloading an operator is that …

Answer 5

at least one operand must be of a class type.

Question 6

What is a binary operator?

Answer 6

With a binary operator, the arguments are listed before and after the operator; with a function the arguments are listed in parentheses after the function name. Examples of binary operators are: +, - , /, %, and so forth.

Question 7

What is special about the return statement in a definition of an overloaded operator?

Answer 7

It may often return an object of a class. This can be done simply using the constructor of the class, and passing it arguments. Such as:

return Money (finalDollars, finalCents);

Question 8

return Money (finalDollars, finalCents);

This object is sometimes called …

Answer 8

An anonymous object, since it is not named by any variable.

Question 9

What is an anonymous object?

Answer 9

An object of a class that is not named by any variable. Can be constructed using the constructor function.

Question 10

const Money operator + (……..)

This is a new use of the const modifier. What is this use called?

Answer 10

This is called “returning a value as const” or “ returning by const value” or “returning by constant value”.

Question 11

Why would you ever want to return by const value?

Answer 11

It provides a kind of automatic error checking. When you construct (m1 + m2) , you normally do not want to inadvertently change it. In this case changing the object (m1 + m2) probably does not matter, but if the returned object is a reference to an existing object then this can cause problems.

Question 12

With objects of a class, the default assignment operator does not …

Answer 12

With objects of a class, the default assignment operator (=) does not make the two objects the same objects, it only copies values of member variables from one object to another object.

Question 13

Returning by const is difficult to understand. What’s a good rule of thumb for this method?

Answer 13

A good rule of thumb is to always return class types by const value unless you have have explicit reason not to do so.

Question 14

There are two types of operators. Which?

Answer 14

1. binary and

2 unary.

Question 15

What are unary operators?

Answer 15

A unary operator is an operator that takes only one operand.

Question 16

Give an example of a unary operator.

Answer 16

• when used on a number, meaning the negative value of that number. Also the operators ++ and –.

Question 17

What is the difference of overloading binary operators as standalone functions defined outside the class, and overloading them as a member operator?

Answer 17

When a binary operator is overloaded as a member operator, there is only one parameter, not two. The calling object serves as the first parameter.

Question 18

What are good arguments for overloading as member functions and not as standalone functions?

Answer 18

Many experts advocate always overloading operators as member operators. It is more in the spirit of object-oriented programming and is a bit more efficient, since the definition can directly reference member variables and need to use accessor and mutator functions.

Question 19

What are the disadvantages of overloading as member functions and not as standalone functions?

Answer 19

coming soon.

Question 20

Which operators is it generally best not to overload?

Answer 20

The && and ||.

Question 21

Why is it generally a bad idea to overload && and ||?

Answer 21

When overloaded these operators perform complete evaluation, and not the normal short-circuit evaluation. This is so contrary to what most programmers expect that it inevitably causes problems. It is best to just not overload these two operators.