fig10_15.cpp

是有关C++编程原理教程的例子程序,全,应该对大家有所帮助

// Fig. 10.15: fig10_15.cpp  
// Friends can access private members of a class.
#include <iostream>
using std::cout;
using std::endl;

// Count class definition 
class Count 
{
   friend void setX( Count &, int ); // friend declaration
public:
   // constructor
   Count() 
      : x( 0 ) // initialize x to 0
   { 
      // empty body
   } // end constructor Count

   // output x 
   void print() const       
   { 
      cout << x << endl; 
   } // end function print
private:
   int x; // data member
}; // end class Count

// function setX can modify private data of Count 
// because setX is declared as a friend of Count (line 10)
void setX( Count &c, int val )
{
   c.x = val; // allowed because setX is a friend of Count
} // end function setX

int main()
{
   Count counter; // create Count object

   cout << "counter.x after instantiation: ";
   counter.print();

   setX( counter, 8 ); // set x using a friend function
   cout << "counter.x after call to setX friend function: ";
   counter.print();
   return 0;
} // end main

/**************************************************************************
 * (C) Copyright 1992-2005 by Deitel & Associates, Inc. and               *
 * Pearson Education, Inc. All Rights Reserved.                           *
 *                                                                        *
 * DISCLAIMER: The authors and publisher of this book have used their     *
 * best efforts in preparing the book. These efforts include the          *
 * development, research, and testing of the theories and programs        *
 * to determine their effectiveness. The authors and publisher make       *
 * no warranty of any kind, expressed or implied, with regard to these    *
 * programs or to the documentation contained in these books. The authors *
 * and publisher shall not be liable in any event for incidental or       *
 * consequential damages in connection with, or arising out of, the       *
 * furnishing, performance, or use of these programs.                     *
 **************************************************************************/