The Scope Resolution Operator. McGraw-Hill The Complete Reference Fourth Edition

C h a p t e r 1 2 : C l a s s e s a n d O b j e c t s

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The Scope Resolution Operator

As you know, the :: operator links a class name with a member name in order to tell the compiler what class the member belongs to. However, the scope resolution operator has another related use: it can allow access to a name in an enclosing scope that is "hidden" by a local declaration of the same name. For example, consider this fragment: int i; // global i void f()

{ int i; // local i

}

.

.

i = 10; // uses local i

.

As the comment suggests, the assignment i = 10 refers to the local i. But what if function f( ) needs to access the global version of i? It may do so by preceding the

i

with the :: operator, as shown here.

int i; // global i void f()

{ int i; // local i

}

.

.

::i = 10; // now refers to global i

.

Nested Classes

It is possible to define one class within another. Doing so creates a nested class. Since a class declaration does, in fact, define a scope, a nested class is valid only within the scope of the enclosing class. Frankly, nested classes are seldom used. Because of

C++'s flexible and powerful inheritance mechanism, the need for nested classes is virtually nonexistent.