fig07_05.cpp

经典vc教程的例子程序

// Fig. 7.5: fig07_05.cpp  
// Friends can access private members of a class.
#include <iostream.h>

// Modified Count class
class Count {
   friend void setX( Count &, int ); // friend declaration
public:
   Count() { x = 0; }                // constructor
   void print() const { cout << x << endl; }  // output
private:
   int x;  // data member
};

// Can modify private data of Count because
// setX is declared as a friend function of Count
void setX( Count &c, int val )
{
   c.x = val;  // legal: setX is a friend of Count
}

int main()
{
   Count counter;

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