virtualbase.cpp

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//: C09:VirtualBase.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// Shows a shared subobject via a virtual base.
#include <iostream>
using namespace std;

class Top {
protected:
  int x;
public:
  Top(int n) { x = n; }
  virtual ~Top() {}
  friend ostream&
  operator<<(ostream& os, const Top& t) {
    return os << t.x;
  }
};

class Left : virtual public Top {
protected:
  int y;
public:
  Left(int m, int n) : Top(m) { y = n; }
};

class Right : virtual public Top {
protected:
  int z;
public:
  Right(int m, int n) : Top(m) { z = n; }
};

class Bottom : public Left, public Right {
  int w;
public:
  Bottom(int i, int j, int k, int m)
  : Top(i), Left(0, j), Right(0, k) { w = m; }
  friend ostream&
  operator<<(ostream& os, const Bottom& b) {
    return os << b.x << ',' << b.y << ',' << b.z
      << ',' << b.w;
  }
};

int main() {
  Bottom b(1, 2, 3, 4);
  cout << sizeof b << endl;
  cout << b << endl;
  cout << static_cast<void*>(&b) << endl;
  Top* p = static_cast<Top*>(&b);
  cout << *p << endl;
  cout << static_cast<void*>(p) << endl;
  cout << dynamic_cast<void*>(p) << endl;
} ///:~