class Empty{}; 等价于: class Empty { public: Empty(); // 构造函数 Empty(const Emtpy& rhs) {...}; // copy构造函数 ~Empty(); // 析构函数 Empty& operator = (const Empty *rhs) {...}; // copy assignment函数 }
为驳回编译器自动提供的机能,可将相应的成员函数申明为private并且不予实现。使用像Uncopyable这样的basic class也是一种做法。
class Uncopyable { protected: Uncopyable(){ } ~Uncopyable(){ } private: Uncopyable(const Uncopyable&); Uncopyable operator= (const Uncopyable&); } class HomeForSale:private Uncopyable { ... // class不再申明copy构造函数或copy assign操作符 };
polymorphic(带多态性质的)base classes应该申明一个virtual析构函数。如果class带有任何virtual函数,他就应该有一个virtual析构函数。
classes的设计目的如果不是作为base classes使用,或不是为了具备多态性(polymorphically),就不该申明virtual析构函数。
class TimeKeeper { public: TimeKeeper(); ~TimeKeeper(); ... }; class AtomicClock: public TimeKeeper {...}; class WaterClock: public TimeKeeper {...}; class WristWatch: public Timekeeper {...}; TimeKeeper *ptk = getTimeKeeper(); delete pkt; // 内存泄漏
class TimeKeeper { public: TimeKeeper(); virtual ~TimeKeeper(); ... }; class AtomicClock: public TimeKeeper {...}; class WaterClock: public TimeKeeper {...}; class WristWatch: public Timekeeper {...}; TimeKeeper *ptk = getTimeKeeper(); delete pkt; // OK