繼承多態(tài)信息工程學(xué)院計(jì)算機(jī)技術(shù)教研室

1、概述 多態(tài)性（Polymorphism）是指一個名字，多種語義；或界面 相同，多種實(shí)現(xiàn)。即當(dāng)發(fā)出同樣的消息被不同類型的對象接 收時，導(dǎo)致完全不同的行為。 多態(tài)性是面向?qū)ο蟪绦蛟O(shè)計(jì)的重要特征之一。 多態(tài)的實(shí)現(xiàn)：函數(shù)重載運(yùn)算符重載虛函數(shù)聯(lián)編是指一個程序模塊、代碼之間互相關(guān)聯(lián)的過程。 靜態(tài)聯(lián)編(Static Binding)：是指程序的匹配、連接在編譯階段，即程序運(yùn)行之前完成，也稱為早期匹配。重載函數(shù)使用靜態(tài)聯(lián)編。 動態(tài)聯(lián)編(Dynamic Binding) ：是指程序聯(lián)編推遲到運(yùn)行時進(jìn)行，所以又稱為晚期聯(lián)編。繼承和虛函數(shù)使用的是動態(tài)聯(lián)編。8.6 聯(lián)編(Binding)普通成員函數(shù)重載可表達(dá)為兩種形

2、式：1. 在一個類說明中重載例如：Show ( int , char ) ;Show ( char * , float ) ;8.7 靜態(tài)聯(lián)編普通成員函數(shù)重載可表達(dá)為兩種形式：1. 在一個類說明中重載例如：Show ( int , char )； 與Show ( char * , float )； 不是同一函數(shù)，編譯能夠區(qū)分2. 基類的成員函數(shù)在派生類重載。有 3 種編譯區(qū)分方法：（1）根據(jù)參數(shù)的特征加以區(qū)分8.7 靜態(tài)聯(lián)編普通成員函數(shù)重載可表達(dá)為兩種形式：1. 在一個類說明中重載2. 基類的成員函數(shù)在派生類重載。有 3 種編譯區(qū)分方法：（1）根據(jù)參數(shù)的特征加以區(qū)分例如：A : Show (

3、)；有別于B : Show ( )；（2）使用“ : ”加以區(qū)分8.7 靜態(tài)聯(lián)編普通成員函數(shù)重載可表達(dá)為兩種形式：1. 在一個類說明中重載2. 基類的成員函數(shù)在派生類重載。有 3 種編譯區(qū)分方法：（1）根據(jù)參數(shù)的特征加以區(qū)分（2）使用“ : ”加以區(qū)分例如：Aobj . Show ( )調(diào)用A : Show ( )Bobj . Show ( )調(diào)用B : Show ( )（3）根據(jù)類對象加以區(qū)分8.7 靜態(tài)聯(lián)編 冠以關(guān)鍵字 virtual 的成員函數(shù)稱為虛函數(shù) 實(shí)現(xiàn)運(yùn)行時多態(tài)的關(guān)鍵首先是要說明虛函數(shù)，另外，必須 用基類指針調(diào)用派生類的不同實(shí)現(xiàn)版本8.8 虛函數(shù)和動態(tài)聯(lián)編 基類指針雖然獲取派生類

4、對象地址，卻只能訪問派生類從基類繼承的成員8.8.1 虛函數(shù)和基類指針#includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d

5、 : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針#includeclass Base public : Base(

6、char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : F

7、irst_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_obj#includeclass Base public : Base(char xx) x = xx; void who() cout Base class:

8、 x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Sec

9、ond derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp定義基類指針#includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class Firs

10、t_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ;

11、p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx,

12、 char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - w

13、ho() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout

14、First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) -

15、 who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: c

16、har y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_

17、objF_objS_objp#includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d pub

18、lic : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : B

19、ase(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz )

20、 : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : Base(char xx) x = xx; void who() cout Base c

21、lass: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cou

22、t Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class First

23、_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p

24、 = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objpvoid who() cout First derived class: x , y n ; #includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: char x; ;class F

25、irst_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who()

26、 ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objpvoid who() cout First derived class: x , y n ; 通過對象調(diào)用成員函數(shù)#includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected: ch

27、ar x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x

28、 , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objpvoid who() cout Second derived class: x , y , z n ; #includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; prot

29、ected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived

30、 class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objpvoid who() cout Second derived class: x , y , z n ; 基類指針做類型轉(zhuǎn)換#includeclass Base public : Base(char xx) x = xx; void who() cout Base

31、 class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() c

32、out Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp通過基類指針只能訪問從基類繼承的成員 #includeclass Base public : Base(char xx) x = xx; void who() cout Base class: x n ; protected:

33、 char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class

34、: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp修改程序定義虛函數(shù)#includeclass Base public : Base(char xx) x = xx; virtual void who() cout Base class: x n ; protected: char x; ;class First_d :

35、public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F

36、_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針基類定義虛函數(shù)#includeclass Base public : Base(char xx) x = xx; virtual void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(x

37、x) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who

38、() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針派生類的重定義版本默認(rèn)為虛函數(shù)#includeclass Base public : Base(char xx) x = xx; virtual void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived clas

39、s: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動

40、8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_obj#includeclass Base public : Base(char xx) x = xx; virtual void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;cla

41、ss Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_o

42、bjp#includeclass Base public : Base(char xx) x = xx; virtual void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public

43、 : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : Base

44、(char xx) x = xx; virtual void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char

45、 zz ) : First_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : Base(char xx) x = xx; virtual void who(

46、) cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; v

47、oid who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objpvoid who() cout First derived class: x , y n ; #includeclass Base public : Base(char xx) x = xx; virtu

48、al void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy

49、 ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objvoid who() cout First derived class: x , y n ; p#includeclass Base public : Base(char xx) x

50、 = xx; virtual void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : Fir

51、st_d( xx, yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp#includeclass Base public : Base(char xx) x = xx; virtual void who() cout Base

52、 class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz; void who() c

53、out Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objpvoid who() coutSecond derived class: x, y, zn ; #includeclass Base public : Base(char xx) x = xx; virtual void wh

54、o() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx, yy ) z = zz;

55、 void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objvoid who() coutSecond derived class: x, y, zn ; p#includeclass Base public : Base(char xx) x = xx; vi

56、rtual void who() cout Base class: x n ; protected: char x; ;class First_d : public Base public : First_d(char xx, char yy):Base(xx) y = yy; void who() cout First derived class: x , y n ; protected: char y; ;class Second_d : public First_d public : Second_d( char xx, char yy, char zz ) : First_d( xx,

57、 yy ) z = zz; void who() cout Second derived class: x , y , z who() ; p = &F_obj ; p - who() ; p = &S_obj ; p - who() ; F_obj.who() ; ( ( Second_d * ) p ) - who() ;演示基類指針的移動 8.8.1 虛函數(shù)和基類指針ATOENDxyzB_objF_objS_objp由于who()的虛特性隨著p指向不同對象，執(zhí)行不同實(shí)現(xiàn)版本 注意： 一個虛函數(shù)，在派生類層界面相同的重載函數(shù)都保持虛特性 虛函數(shù)必須是類的成員函數(shù)，不能是全局函數(shù)和靜態(tài)函數(shù)

58、不能將友元說明為虛函數(shù)，但虛函數(shù)可以是另一個類的友元 析構(gòu)函數(shù)可以是虛函數(shù)，但構(gòu)造函數(shù)不能是虛函數(shù) 動態(tài)聯(lián)編只能通過指針或引用來操作虛函數(shù)，如果采用其他標(biāo)識對象來操作虛函數(shù)，將采用靜態(tài)聯(lián)編方式調(diào)用虛函數(shù)。8.8.1 虛函數(shù)和基類指針 在派生類中重載基類的虛函數(shù)要求函數(shù)名、返回類型、參數(shù) 個數(shù)、參數(shù)類型和順序完全相同 如果僅僅返回類型不同，C+認(rèn)為是錯誤重載 如果函數(shù)原型不同，僅函數(shù)名相同，丟失虛特性 8.8.2 虛函數(shù)的重載特性void g ( ) derived d ; base * bp = & d ; / 基類指針指向派生類對象 bp - vf1 ( ) ; / 調(diào)用 derived :

59、 vf1 ( ) bp - vf2 ( ) ; / 調(diào)用 base : vf2 ( ) bp - f ( ) ; / 調(diào)用 base : f ( ) ; 例：class base public : virtual void vf1 ( ) ; virtual void vf2 ( ) ; virtual void vf3 ( ) ; void f ( ) ; ;class derived : public base public : void vf1 ( ) ;/ 虛函數(shù) void vf2 ( int ) ;/ 重載，參數(shù)不同，虛特性丟失 char vf3 ( ) ;/ error，僅返回類型

60、不同 void f ( ) ;/ 非虛函數(shù)重載 ;8.8.2 虛函數(shù)的重載特性 構(gòu)造函數(shù)不能是虛函數(shù)。建立一個派生類對象時，必須從類 層次的根開始，沿著繼承路徑逐個調(diào)用基類的構(gòu)造函數(shù) 析構(gòu)函數(shù)可以是虛的。虛析構(gòu)函數(shù)用于指引 delete 運(yùn)算符正 確析構(gòu)動態(tài)對象 8.8.3 虛析構(gòu)函數(shù)#includeclass A public: A() cout A:A() is called.n ; ;class B : public A public: B() cout B:B() is called.n ; ;void main() A *Ap = new B ; B *Bp2 = new B ; c