The invocation of constructors and destructors in C + + in polymorphic

To do an experiment, look at the structure of member variables, the structure of the parent subclass, and the effect of the virtual function on the call.

1#include <iostream>2 using namespacestd;3 4 classMember5 {6  Public:7Member (intN): M_n1 (n)8     {9cout<<"Member::member ("<<m_n1<<")"<<Endl;Ten     } One~Member () A     { -cout<<"Member::~member ("<<m_n1<<")"<<Endl; -     } the Private: -     Const intm_n1; - }; -  + classBase - { +  Public: ABase (): M_m1 (1) at     { -cout<<"base::base ()"<<Endl; - onconstruct (); -     } -~base ()//This is not a virtual function . -     { incout<<"base::~base ()"<<Endl; - ondistruct (); to     } +     Virtual voidonconstruct () -     { thecout<<"base::onconstruct ()"<<Endl; *     } $     Virtual voidondistruct ()Panax Notoginseng     { -cout<<"base::ondistruct ()"<<Endl; the     } +     Virtual voidFoo1 () A     { thecout<<"base::foo1 ()"<<Endl; +     } -     voidFoo2 () $     { $cout<<"Base::foo2 ()"<<Endl; -     } -  the Private: -Member m_m1;//This is a class object .Wuyi }; the  - classDriveD: PublicBase Wu { -  Public: AboutDriveD (): m_m2 (2) $     { -cout<<"drived::D rived ()"<<Endl; - onconstruct (); -     } A~drived () +     { thecout<<"drived::~drived ()"<<Endl; - ondistruct (); $     } the     Virtual voidonconstruct () the     { thecout<<"drived::onconstruct ()"<<Endl; the     } -     Virtual voidondistruct () in     { thecout<<"drived::ondistruct ()"<<Endl; the     } About     Virtual voidFoo1 () the     { thecout<<"drived::foo1 ()"<<Endl; the     } +     voidFoo2 ()//This is not a virtual function . -     { thecout<<"Drived::foo2 ()"<<Endl;Bayi     } the Private: theMember m_m2;//This is a class object . - }; -  the intMainintargcChar*argv[]) the { thebase* p =Newdrived; theP->Foo1 (); -P->Foo2 (); the     Deletep; the     return 0; the}

The running output of this code is:

1Member::member (1) //The initialization list of the parent class is executed 2 base::base () //Parent class construction 3 the Base::onconstruct ()///parent class will only call functions of the parent class. Parent class constructed 4Member::member (2) //Sub-class construction initialization list 5 drived::D rived () /Sub-class construction 6 drived::onconstruct ()//subclass constructors only call functions of subclasses. Sub-class construction complete 7 drived::foo1 ()//polymorphic, calling subclass overridden function 8 Base::foo2 () //Not polymorphic, calling the parent version of the function 9base::~Base () //Parent class start destructor Ten base::ondistruct ()//Parent class destructors only call functions in the parent class  OneMember::~member (1)//Parent class member anti-initialization

Students can see that the destructor of the subclass is not executed, how can it be executed? Modify the parent class's destructor to virtual:

 -     // This is not a virtual function .

This is done again and you can see the result if (the new output is commented out):

1Member::member (1)2 base::base ()3 base::onconstruct ()4Member::member (2)5 drived::D rived ()6 drived::onconstruct ()7 drived::foo1 ()8 Base::foo2 ()9drived::~drived () //subclass destructor, executed before the parent class Ten drived::ondistruct ()//subclass destructors only call functions of subclasses  OneMember::~member (2) //Sub-class member anti-initialization  Abase::~Base () - base::ondistruct () -Member::~member (1)

Summary:

Implements polymorphism by pointing to a subclass object through the parent class pointer.

When Polymorphic, the parent class destructor is a virtual function to ensure that the subclass destructor is called.

The construction order is: After the Father class subclass (this is the most important process, the latter two are again this premise); The initialization list is executed before the constructor, and the values in the constructor call the functions of this class, whether or not it is a virtual function.

The destructor sequence is: Subclass Stepfather Class (note virtual destruction); Only the functions of this class are called in the destructor; This class is then refactored to initialize the members of the list.

The invocation of constructors and destructors in C + + in polymorphic