Sams Teach Yourself C++ in 21 Days

Advanced Inheritance 585

16

s1: String One

s2: String Two

c1: C-String One

s3: String One String Two

s4: String One C-String One

s5: C-String One String Two

The implementation of all the string methods except operator+are unchanged

from Listing 16.1. On line 20, a new operator+is overloaded to take two con-

stant string references and to return a string, and this function is declared to be a friend.

Note that this operator+is not a member function of this or any other class. It is

declared within the declaration of the Stringclass only so that it can be made a friend,

but because it is declared, no other function prototype is needed.

The implementation of this operator+is on lines 143–154. Note that it is similar to the

earlier operator+, except that it takes two strings and accesses them both through their

public accessor methods.

The driver program demonstrates the use of this function on line 172, where operator+

is now called on a C-style string!

OUTPUT

ANALYSIS

Friend Functions

Declare a function to be a friend by using the keyword friendand then the full specification

of the function. Declaring a function to be a friend does not give the friendfunction access to

your thispointer, but it does provide full access to all private and protected member data and

functions.

Example

class PartNode

{ // ...

// make another class’s member function a _friend

friend void PartsList::Insert(Part *);

// make a global function a friend

friend int SomeFunction();

// ...

};

Overloading the Insertion Operator ....................................................................

You are finally ready to give your Stringclass the capability to use coutthe same as

any other type. Until now, when you’ve wanted to print a string, you’ve been forced to

write the following:

cout << theString.GetString();