Sams Teach Yourself C++ in 21 Days

Special Classes and Functions 511

15

There are 5 cats left!

Deleting the one that is 2 years old

There are 4 cats left!

Deleting the one that is 3 years old

There are 3 cats left!

Deleting the one that is 4 years old

There are 2 cats left!

Deleting the one that is 5 years old

There are 1 cats left!

Deleting the one that is 6 years old

On line 16, the static member variable HowManyCatsis declared to have private

access. Now, you cannot access this variable from nonmember functions, such as

TelepathicFunction()from the previous listing.

Even though HowManyCatsis static, it is still within the scope of the class. As such, any

class function, such as GetHowMany(), can access it, just as member functions can access

any member data. However, for a function outside of a Catobject to call GetHowMany(),

it must have a Catobject on which to call the function.

OUTPUT

ANALYSIS

DOuse static member variables to share

data among all instances of a class.

DOmake static member variables pro-

tected or private if you want to restrict

access to them.

DON’Tuse static member variables to

store data for one object. Static member

data is shared among all objects of its

class.

DO DON’T

Using Static Member Functions ..........................................................................

Static member functions are like static member variables: They exist not in an object but

in the scope of the class. Thus, they can be called without having an object of that class,

as illustrated in Listing 15.4.

LISTING15.4 Static Member Functions

0: //Listing 15.4 static data members

1:

2: #include <iostream>

3:

4: class Cat

5: {

6: public:

7: Cat(int age):itsAge(age){HowManyCats++; }