重载赋值运算符--引用计数

#include <iostream>#include <string>using namespace std;class Dog{private:string nm;int refcount; // 引用计数，Dog(const string& name) : nm(name), refcount(1){cout << "Creating Dog: " << *this << endl;}public:static Dog* make(const string& name){return new Dog(name); // 这个表示只允许在堆上创建对象，不允许在栈上创建对象，}~Dog(){cout << "Deleting Dog: " << *this << endl;}Dog(const Dog& d) : nm(d.nm + " copy "), refcount(1){cout << "Dog copy-constructor: " << *this << endl;}void attach(){++refcount;cout << "Attached Dog: " << *this << endl;}void detach(){cout << "Detching Dog: " << *this << endl;if (--refcount == 0)delete this;}void rename(const string& newName){nm = newName;cout << "Dog renamed to: " << *this << endl;}Dog* unalias()  // 这个是取消别名，{cout << "Unaliasing Dog: " << *this << endl;if (refcount == 1) return this;--refcount; // 这是引用计数减一，return new Dog(*this);  // 创建新的}friend ostream& operator<<(ostream& os, const Dog& d){return os << "[" << d.nm << "], rc = " << d.refcount;}};class DogHouse{private:Dog* p;string houseName;public:DogHouse(Dog* dog, const string& house) :p(dog), houseName(house){}DogHouse(const DogHouse& dh) :p(dh.p), houseName(dh.houseName + " copy-constructed"){p->attach();cout << "DogHouse copy-constructor: " << *this << endl;} DogHouse& operator=(const DogHouse& dh){if (&dh != this){p->detach();  // 这个是减一，p = dh.p;p->attach();}cout << "DogHouse operator= : " << *this << endl;return *this;}~DogHouse(){cout << "DogHouse destructor: " << *this << endl;p->detach();}void rename(const string& newName){houseName = newName;}// copy - on -writevoid unalias(){p = p->unalias(); // copy-on-write}Dog* getDog() {unalias(); // 这个去除别名，判断要不要进行复制，return p;}void renameDog(const string& newName){unalias();p->rename(newName);}friend ostream& operator<<(ostream& os, const DogHouse& dh){return os << "[" << dh.houseName << "] constains " << *dh.p;}};int main(){DogHouse a(Dog::make("A"), "AHouse");cout << a << endl << endl;DogHouse b(a);DogHouse c = a;cout << "..... " << endl;c.renameDog("CDog");cout << " a: " << a << endl << endl;cout << " c: " << c << endl << endl;return 0;}