addv.cpp

来自「Think in C++文中代码实现」· C++ 代码 · 共 65 行

// File from page 557 in "Thinking in C++" by Bruce Eckel
//////////////////////////////////////////////////
// From the compressed package ECKELT02.ZIP 4/11/95
// (Original ECKELT01.ZIP dated 2/21/95)
// Copyright (c) Bruce Eckel, 1995 
// Source code file from the book "Thinking in C++", 
// Prentice Hall, 1995, ISBN: 0-13-917709-4
// All rights reserved EXCEPT as allowed by the following 
// statements: You may freely use this file for your own 
// work, including modifications and distribution in 
// executable form only. You may copy and distribute this 
// file, as long as it is only distributed in the complete 
// (compressed) package with the other files from this 
// book and you do not remove this copyright and notice. 
// You may not distribute modified versions of the source 
// code in this package. This package may be freely placed 
// on bulletin boards, internet nodes, shareware disks and 
// product vendor disks. You may not use this file in 
// printed media without the express permission of the 
// author. Bruce Eckel makes no 
// representation about the suitability of this software 
// for any purpose. It is provided "as is" without express 
// or implied warranty of any kind. The entire risk as to 
// the quality and performance of the software is with 
// you. Should the software prove defective, you assume 
// the cost of all necessary servicing, repair, or 
// correction. 
// If you think you've found an error, please 
// email all modified files with loudly commented changes 
// to: [e-mail] (please use the same 
// address for non-code errors found in the book).
//////////////////////////////////////////////////

//: ADDV.CPP -- Adding virtuals in derivation
#include <iostream.h>

class base {
  int i;
public:
  base(int I) : i(I) {}
  virtual int value() const { return i; }
};

class derived : public base {
public:
  derived(int I) : base(I) {}
  int value() const {
    return base::value() * 2;
  }
  // New virtual function in the derived class:
  virtual int shift(int x) const {
    return base::value() << x;
  }
};

main() {
  base* B[] = { new base(7), new derived(7) };
  cout << "B[0]->value() = "
       << B[0]->value() << endl;
  cout << "B[1]->value() = "
       << B[1]->value() << endl;
//! cout << "B[1]->shift(3) = "
//!      << B[1]->shift(3) << endl; // Illegal
}