Sams Teach Yourself C++ in 21 Days

Exploiting References 279

9

Making a cat...

Simple Cat constructor...

Frisky is 1 years old

Frisky is 5 years old

Calling FunctionTwo...

FunctionTwo. Returning...

Frisky is now 5 years old

Frisky is 5 years old

Simple Cat Destructor...

The output is identical to that produced by Listing 9.11. The only significant

change is that FunctionTwo()now takes and returns a reference to a constant

object. Once again, working with references is somewhat simpler than working with

pointers, and the same savings and efficiency are achieved, as well as the safety provided

by using const.

OUTPUT

ANALYSIS

constReferences

C++ programmers do not usually differentiate between “constant reference to a

SimpleCatobject” and “reference to a constant SimpleCatobject.” References them-

selves can never be reassigned to refer to another object, and so they are always con-

stant. If the keyword constis applied to a reference, it is to make the object referred to

constant.

Knowing When to Use References Versus Pointers ............................................

Experienced C++ programmers strongly prefer references to pointers. References are

cleaner and easier to use, and they do a better job of hiding information, as you saw in

the previous example.

References cannot be reassigned, however. If you need to point first to one object and

then to another, you must use a pointer. References cannot be null, so if any chance

exists that the object in question might be null, you must not use a reference. You must

use a pointer.

An example of the latter concern is the operator new. If newcannot allocate memory on

the free store, it returns a null pointer. Because a reference shouldn’t be null, you must

not initialize a reference to this memory until you’ve checked that it is not null. The fol-

lowing example shows how to handle this:

int *pInt = new int;

if (pInt != NULL)

int &rInt = *pInt;