Sams Teach Yourself C++ in 21 Days

Creating and Using Namespaces 655

18

As an alternative, you could fully qualify the names that you use, as in Listing 18.11.

LISTING18.11 Qualifying Namespace Items Inline

0: #include <iostream>

1: int main( )

2: {

3: int value = 0 ;

4: std::cout << “How many eggs did you want?” << std::endl ;

5: std::cin >> value ;

6: std::cout << value << “ eggs, sunny-side up!” << std::endl ;

7: return( 0 ) ;

8: }

How many eggs did you want?

4

4 eggs, sunny-side up!

Qualifying namespace items inline might be appropriate for shorter programs but

can become quite cumbersome for any significant amount of code. Imagine hav-

ing to prefix std::for every name you use that is found in the Standard Library!

Summary ..............................................................................................................

Today’s lesson expanded on information you have been previously exposed to throughout

this book.

Creating a namespace is very similar to a class declaration. A couple of differences are

worth noting. First, a semicolon does not follow a namespace’s closing brace. Second, a

namespace is open, whereas a class is closed. This means that you can continue to define

the namespace in other files or in separate sections of a single file.

Anything that can be declared can be inserted into a namespace. If you are designing

classes for a reusable library, you should be using the namespace feature. Functions

declared within a namespace should be defined outside of that namespace’s body. This

promotes a separation of interface from implementation and also keeps the namespace

from becoming cluttered.

The usingdirectiveis used to expose all names in a namespace into the current scope.

This effectively fills the global namespace with all names found in the named name-

space. It is generally bad practice to use the usingdirective, especially with respect to

the Standard Library. Use usingdeclarationsinstead.

A usingdeclaration is used to expose a specific namespace item into the current scope.

This allows you to refer to the object by its name only.

OUTPUT

ANALYSIS