Datasheet

Const References

You will often find code that uses const reference parameters. At first, that seems like a contradiction.

Reference parameters allow you to change the value of a variable from within another context.

const

seems to prevent such changes.

The main value in

const reference parameters is efficiency. When you pass a variable into a function,

an entire copy is made. When you pass a reference, you are really just passing a pointer to the original

so the computer doesn’t need to make the copy. By passing a

const reference, you get the best of both

worlds — no copy is made but the original variable cannot be changed.

const references become more important when you are dealing with objects because they can be large

and making copies of them can have unwanted side effects. Subtle issues like this are covered in

Chapter 12.

C++ as an Object-Oriented Language

If you are a C programmer, you may have viewed the features covered so far in this chapter as convenient

additions to the C language. As the name C++ implies, in many ways the language is just a “better C.”

There is one major point that this view overlooks. Unlike C, C++ is an object-oriented language.

Object-oriented programming (OOP) is a very different, arguably more natural, way to write code.

If you are used to procedural languages such as C or Pascal, don’t worry. Chapter 3 covers all the back-

ground information you need to know to shift your mindset to the object-oriented paradigm. If you

already know the theory of OOP, the rest of this section will get you up to speed (or refresh your mem-

ory) on basic C++ object syntax.

Declaring a Class

A class defines the characteristics of an object. It is somewhat analogous to a struct except a class defines

behaviors in addition to properties. In C++, classes are usually declared in a header file and fully

defined in a corresponding source file.

A basic class definition for an airline ticket class is shown below. The class can calculate the price of the

ticket based on the number of miles in the flight and whether or not the customer is a member of the

“Elite Super Rewards Program.” The definition begins by declaring the class name. Inside a set of curly

braces, the data members (properties) of the class and its methods (behaviors) are declared. Each data

member and method is associated with a particular access level:

public, protected, or private. These

labels can occur in any order and can be repeated.

// AirlineTicket.h

#include <string>

class AirlineTicket

{

public:

AirlineTicket();

Chapter 1

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