virtualbase2.cpp

来自「C语言数值算法程序大全（第二版）,课本文件」· C++ 代码 · 共 56 行

//: C09:VirtualBase2.cpp
// From "Thinking in C++, 2nd Edition, Volume 2"
// by Bruce Eckel & Chuck Allison, (c) 2003 MindView, Inc.
// Available at www.BruceEckel.com.
// Shows how not to implement operator<<
#include <iostream>
using namespace std;

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

class Left : virtual public Top {
  int y;
public:
  Left(int m, int n) : Top(m) { y = n; }
  friend ostream&
  operator<<(ostream& os, const Left& l) {
    return os << static_cast<const Top&>(l) << ',' << l.y;
  }
};

class Right : virtual public Top {
  int z;
public:
  Right(int m, int n) : Top(m) { z = n; }
  friend ostream&
  operator<<(ostream& os, const Right& r) {
    return os << static_cast<const Top&>(r) << ',' << r.z;
  }
};

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 << static_cast<const Left&>(b)
      << ',' << static_cast<const Right&>(b)
      << ',' << b.w;
  }
};

int main() {
  Bottom b(1, 2, 3, 4);
  cout << b << endl;  // 1,2,1,3,4
} ///:~