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Creating and Using Namespaces 645

18

Defining Functions Outside a Namespace ....................................................

You should define namespace functions outside the namespace body. Doing so illustrates

a clear separation of the declaration of the function and its definition—and also keeps the

namespace body uncluttered. Separating the function definition from the namespace also

enables you to put the namespace and its embodied declarations within a header file; the

definitions can be placed into an implementation file. Listings 18.7a and 18.7b illustrate

this separation.

LISTING18.7A Declaring a Header in a Namespace

0: // file header.h

1: namespace Window {

2: void move( int x, int y) ;

3: // other declarations ...

4: }

LISTING18.7B Declaring the Implementation in the Source File

0: // file impl.cpp

1: void Window::move( int x, int y )

2: {

3: // code to move the window

4: }

Adding New Members ..................................................................................

New members can be added to a namespace only within the namespace’s body. You can-

not define new members using qualifier syntax. The most you can expect from this style

of definition is a complaint from your compiler. The following example demonstrates

this error:

namespace Window

{

// lots of declarations

}

//...some code

int Window::newIntegerInNamespace ; // sorry, can’t do this

The preceding line of code is illegal. Your (conforming) compiler issues a diagnostic

reflecting the error. To correct the error—or avoid it altogether—move the declaration

within the namespace body.