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Data Types, Variables and Operators 7

 

 

The discussion and the codes used supposed to be based on the new C++ .NET. The following are the topics in this part.

1. Nested Class Declarations

2. friend

3. Type Names in Class Scope

4. Integer Limits

5. Floating Limits

BufferedIO::BufferedInput and BufferedIO::BufferedOutput are declared within BufferedIO. These class names are not visible outside the scope of class BufferedIO. However, an object of type BufferedIO does not contain any objects of types BufferedInput or BufferedOutput. Nested classes can directly use names, type names, names of static members, and enumerators only from the enclosing class. To use names of other class members, you must use pointers, references, or object names. In the preceding BufferedIO example, the enumeration IOError can be accessed directly by member functions in the nested classes, BufferedIO::BufferedInput or BufferedIO::BufferedOutput, as shown in function good. Nested classes declare only types within class scope. They do not cause contained objects of the nested class to be created. The preceding example declares two nested classes but does not declare any objects of these class types.

 

friend Keyword

 

In some circumstances, it is more convenient to grant member-level access to functions that are not members of a class or to all functions in a separate class. The friend keyword allows a function or class to gain access to the private and protected members of a class. You can declare friend functions or friend classes to access not only public members but also protected and private class members.

friend class-name;

friend function-declarator;

 

 

 

 

A friend function is a function that is not a member of a class but has access to the class's private and protected members. Friend functions are not considered class members; they are normal external functions that are given special access privileges. Friends are not in the class's scope, and they are not called using the member-selection operators (. and –>) unless they are members of another class. A friend function is declared by the class that is granting access. The friend declaration can be placed anywhere in the class declaration. It is not affected by the access control keywords. The following example shows a Point class and a friend function, ChangePrivate. The friend function has access to the private data member of the Point object it receives as a parameter.

// Variables.cpp : main project file.

// friend functions

// compile with: /clr

#include "stdafx.h"

 

using namespace System;

 

class Point

{

      friend void ChangePrivate(Point &);

      public:

            Point( void ) : m_i(0) {}

            void PrintPrivate( void ){Console::WriteLine("m_i = {0}", m_i); }

      private:

            int m_i;

};

 

void ChangePrivate(Point &i) {i.m_i++;}

 

int main()

{

      Point sPoint;

      sPoint.PrintPrivate();

      ChangePrivate(sPoint);

      sPoint.PrintPrivate();

     

      return 0;

}

 

Output:

 

 

 

 

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Type Names in Class Scope

 

Type names defined within class scope are considered local to their class. They cannot be used outside that class. The following example demonstrates this concept:

// type names in class scope

// C2146 expected

class Tree

{

      public:

            typedef Tree * PTREE;

            PTREE  Left;

            PTREE  Right;

            void  *vData;

};

 

PTREE pTree;  // not in class scope

Integer Limits

 

The limits for integer types are listed in the following table. These limits are also defined in the standard header file limits.h. It is Microsoft implementation.

 

 

 

 

 

If a value exceeds the largest integer representation, the Microsoft compiler generates an error.

 

Floating Limits

 

The following table lists the limits on the values of floating-point constants. These limits are also defined in the standard header file float.h. It is Microsoft implementation.

 

 

Take note that the information in the table may differ or updated in future or new versions of the product.

 

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 | Part 10

 

 

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