C++私有成员

#include <iostream>

using namespace std;

class Box {
   public:
      double length;
      void setWidth( double wid );
      double getWidth( void );

   private:
      double width;
};

// Member functions deFinitions
double Box::getWidth(void) {
   return width ;
}

void Box::setWidth( double wid ) {
   width = wid;
}

// Main function for the program
int main() {
   Box Box;

   // set Box length without member function
   Box.length = 10.0; // OK: because length is public
   cout << Length of Box :  << Box.length <<endl;

   // set Box width without member function
   // Box.width = 10.0; // Error: because width is private
   Box.setWidth(10.0);  // Use member function to set it.
   cout << Width of Box :  << Box.getWidth() <<endl;

   return 0;
}