虚函数:多态性质,运行时编译
虚函数的实现:虚函数指针和虚函数表
虚函数指针 (virtual function pointer) 从本质上来说就只是一个指向函数的指针,与普通的指针并无区别。它指向用户所定义的虚函数,具体是在子类里的实现,当子类调用虚函数的时候,实际上是通过调用该虚函数指针从而找到接口。
虚函数指针是确实存在的数据类型,在一个被实例化的对象中,它总是被存放在该对象的地址首位,这种做法的目的是为了保证运行的快速性。与对象的成员不同,虚函数指针对外部是完全不可见的,除非通过直接访问地址的做法或者在DEBUG模式中,否则它是不可见的也不能被外界调用。
------文字转自博客https://blog.csdn.net/weixin_43329614/article/details/89103574
着重理解虚函数表,实例化的类对象共用一个虚函数表。空对象会有一个虚函数指针。另外,子类和父类的虚函数需一模一样,不然就只能算重载,子类并不能覆盖父类虚函数来实现多态。
侯捷《C++最佳编程实践》视频看讲解。
虚析构函数:只有当一个类被定义为基类的时候,才会把析构函数写成虚析构函数。保证基类指针被正确释放,不加virtual有内存泄漏风险。
在看AMCL时,用到虚函数,整理下
1、传感器类
// Base class for all AMCL sensors class AMCLSensor { // Default constructor public: AMCLSensor(); // Default destructor public: virtual ~AMCLSensor(); // Update the filter based on the action model. Returns true if the filter // has been updated. public: virtual bool UpdateAction(pf_t *pf, AMCLSensorData *data); // Initialize the filter based on the sensor model. Returns true if the // filter has been initialized. public: virtual bool InitSensor(pf_t *pf, AMCLSensorData *data); // Update the filter based on the sensor model. Returns true if the // filter has been updated. public: virtual bool UpdateSensor(pf_t *pf, AMCLSensorData *data); // Flag is true if this is the action sensor public: bool is_action; // Action pose (action sensors only) public: pf_vector_t pose; // AMCL Base //protected: AdaptiveMCL & AMCL; #ifdef INCLUDE_RTKGUI // Setup the GUI public: virtual void SetupGUI(rtk_canvas_t *canvas, rtk_fig_t *robot_fig); // Finalize the GUI public: virtual void ShutdownGUI(rtk_canvas_t *canvas, rtk_fig_t *robot_fig); // Draw sensor data public: virtual void UpdateGUI(rtk_canvas_t *canvas, rtk_fig_t *robot_fig, AMCLSensorData *data); #endif };
继承类有两个
class AMCLLaser : public AMCLSensor class AMCLOdom : public AMCLSensor
2、传感器数据类
// Base class for all AMCL sensor measurements class AMCLSensorData { // Pointer to sensor that generated the data public: AMCLSensor *sensor; virtual ~AMCLSensorData() {} // Data timestamp public: double time; };
继承类也有两个
class AMCLLaserData : public AMCLSensorData class AMCLOdomData : public AMCLSensorData