C++保护成员

#include <iostream>

using namespace std;

class Box {
   protected:
      double wIDth;
};

class SmallBox:Box {    // SmallBox is the derived class.
   public:
      voID setSmallWIDth( double wID );
      double getSmallWIDth( voID );
};

// Member functions of child class
double SmallBox::getSmallWIDth(voID) {
   return wIDth ;
}

voID SmallBox::setSmallWIDth( double wID ) {
   wIDth = wID;
}

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

   // set Box wIDth using member function
   Box.setSmallWIDth(5.0);
   cout << "WIDth of Box : "<< Box.getSmallWIDth() << endl;

   return 0;
}