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Advanced Inheritance 579

16

(0)Quit (1)Car (2)Plane: 1

New PartNumber?: 1234

Model Year?: 94

(0)Quit (1)Car (2)Plane: 1

New PartNumber?: 4434

Model Year?: 93

(0)Quit (1)Car (2)Plane: 1

New PartNumber?: 1234

Model Year?: 94

1234 was the first entry. Rejected!

(0)Quit (1)Car (2)Plane: 1

New PartNumber?: 2345

Model Year?: 93

(0)Quit (1)Car (2)Plane: 0

Part Number: 1234

Model Year: 94

Part Number: 2345

Model Year: 93

Part Number: 4434

Model Year: 93

On line 79, the class PartsListis declared to be a friend to the PartNode

class.

This listing places the friend declaration in the public section, but this is not required; it

can be put anywhere in the class declaration without changing the meaning of the state-

ment. Because of this statement, all the private member data and functions are available

to any member function of class PartsList.

On line 157, the implementation of the member function GetFirst()reflects this

change. Rather than returning pHead->GetPart, this function can now return the other-

wise private member data by writing pHead->itsPart. Similarly, the Insert()function

can now write pNode->itsNext = pHead, rather than writing pNode->SetNext(pHead).

Admittedly, these are trivial changes, and a good enough reason does not exist to make

PartsLista friend of PartNode, but they do serve to illustrate how the keyword friend

works.

Declarations of friendclasses should be used with extreme caution. If two classes are

inextricably entwined, and one must frequently access data in the other, good reason

might exist to use this declaration. But use it sparingly; it is often just as easy to use the

public accessor methods, and doing so enables you to change one class without having to

recompile the other.

OUTPUT

ANALYSIS