copyingwithpointers.cpp

Thinking in C++, 2nd Edition, Volume 2. 英文doc版 每章源代码

//: C12:CopyingWithPointers.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 2000
// Copyright notice in Copyright.txt
// Solving the pointer aliasing problem by
// duplicating what is pointed to during 
// assignment and copy-construction.
#include "../require.h"
#include <string>
#include <iostream>
using namespace std;

class Dog {
  string nm;
public:
  Dog(const string& name) : nm(name) {
    cout << "Creating Dog: " << *this << endl;
  }
  // Synthesized copy-constructor & operator= 
  // are correct.
  // Create a Dog from a Dog pointer:
  Dog(const Dog* dp, const string& msg) 
    : nm(dp->nm + msg) {
    cout << "Copied dog " << *this << " from "
         << *dp << endl;
  }
  ~Dog() { 
    cout << "Deleting Dog: " << *this << endl;
  }
  void rename(const string& newName) {
    nm = newName;
    cout << "Dog renamed to: " << *this << endl;
  }
  friend ostream&
  operator<<(ostream& os, const Dog& d) {
    return os << "[" << d.nm << "]";
  }
};

class DogHouse {
  Dog* p;
  string houseName;
public:
  DogHouse(Dog* dog, const string& house)
   : p(dog), houseName(house) {}
  DogHouse(const DogHouse& dh)
    : p(new Dog(dh.p, " copy-constructed")),
      houseName(dh.houseName 
        + " copy-constructed") {}
  DogHouse& operator=(const DogHouse& dh) {
    // Check for self-assignment:
    if(&dh != this) {
      p = new Dog(dh.p, " assigned");
      houseName = dh.houseName + " assigned";
    }
    return *this;
  }
  void renameHouse(const string& newName) {
    houseName = newName;
  }
  Dog* getDog() const { return p; }
  ~DogHouse() { delete p; }
  friend ostream&
  operator<<(ostream& os, const DogHouse& dh) {
    return os << "[" << dh.houseName 
      << "] contains " << *dh.p;
  }
}; 

int main() {
  DogHouse fidos(new Dog("Fido"), "FidoHouse");
  cout << fidos << endl;
  DogHouse fidos2 = fidos; // Copy construction
  cout << fidos2 << endl;
  fidos2.getDog()->rename("Spot");
  fidos2.renameHouse("SpotHouse");
  cout << fidos2 << endl;
  fidos = fidos2; // Assignment
  cout << fidos << endl;
  fidos.getDog()->rename("Max");
  fidos2.renameHouse("MaxHouse");
} ///:~