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阿新 • • 發佈:2021-07-14
虛擬函式:多型性質,執行時編譯
虛擬函式的實現:虛擬函式指標和虛擬函式表
虛擬函式指標 (virtual function pointer) 從本質上來說就只是一個指向函式的指標,與普通的指標並無區別。它指向使用者所定義的虛擬函式,具體是在子類裡的實現,當子類呼叫虛擬函式的時候,實際上是通過呼叫該虛擬函式指標從而找到介面。
虛擬函式指標是確實存在的資料型別,在一個被例項化的物件中,它總是被存放在該物件的地址首位,這種做法的目的是為了保證執行的快速性。與物件的成員不同,虛擬函式指標對外部是完全不可見的,除非通過直接訪問地址的做法或者在DEBUG模式中,否則它是不可見的也不能被外界呼叫。
------文字轉自部落格https://blog.csdn.net/weixin_43329614/article/details/89103574
著重理解虛擬函式表,例項化的類物件共用一個虛擬函式表。空物件會有一個虛擬函式指標。另外,子類和父類的虛擬函式需一模一樣,不然就只能算過載,子類並不能覆蓋父類虛擬函式來實現多型。
侯捷《C++最佳程式設計實踐》視訊看講解。
虛解構函式:只有當一個類被定義為基類的時候,才會把解構函式寫成虛解構函式。保證基類指標被正確釋放,不加virtual有記憶體洩漏風險。
在看AMCL時,用到虛擬函式,整理下
1、感測器類
// 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 };
繼承類有兩個
class AMCLLaser : public AMCLSensor class AMCLOdom : public AMCLSensor
2、感測器資料類
// 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; };
繼承類也有兩個
class AMCLLaserData : public AMCLSensorData class AMCLOdomData : public AMCLSensorData