Test the C ++ virtual function table

/* Goal, C ++ virtual function table test, test part, other circumstances will have the opportunity to learn again. Date, 2013-3-7http: // empty <iostream> Using STD: cout; Using STD: Endl; typedef void (* voidfun) (); // an empty class, see what information can be mined to compare it with other situations. Class A1 {}; // class A2 with a non-virtual function {public: void F () {cout <"A2: F () "<Endl ;}; // class A3 {public: Virtual void F () {cout <" A3: F () with one virtual function () "<Endl ;};// class A4 {public: Virtual void F2 () {cout <" A4: F2 () with two virtual functions () "<Endl;} virtual void F1 () {cout <" A4: F1 () "<Endl ;}; // single inheritance, do not overwrite the base class virtual function class A5: Public A3 {public: Virtual void g () {cout <"A5: G ()" <Endl ;}}; // single inheritance, does not cover basic class virtual functions, Level 3 class A51: Public A5 {Public: Virtual void H () {cout <"A51: H ()" <Endl ;}; // a single inheritance that covers the base class virtual function class A6: public A3 {public: Virtual void g () {cout <"A6: G ()" <Endl;} virtual void F () {cout <"A6 :: F () "<Endl ;};// multi-inheritance, does not overwrite the base class virtual function class A7: Public A3, public A4 {public: Virtual void G1 () {cout <"A7: G1 ()" <Endl;} virtual void g () {cout <"A7: G () "<Endl ;}}; // multi-inheritance, covering the class A8: Public A3, public A4 {public: Virtual void F1 () {Cout <"A8: F1 ()" <Endl;} virtual void F () {cout <"A8: F ()" <Endl ;} virtual void g () {cout <"A8: G ()" <Endl ;}}; int main () {// pointer to the table of the virtual function table. It points to the table of a virtual function table, and the element in the table points to the virtual function table. // The virtual function table consists of the virtual function addresses of the class. Int ** pvtable; // A1 A1 in case of empty classes; // although there is nothing, the size of the empty class object is 1. Why is it not 0, but 1 rather than 2? // I do not know the specific details. For the empty Class Object array a [10], the space of the empty class can be distinguished by a [0], a [1]. Cout <"Empty Class A1 size:" <sizeof (A1) <Endl; cout <"A1's virtual function table address:" <(int *) (& A1) <Endl; cout <Endl; // class A2 with a non-virtual function; // because there is no data member, the size is still 1, the member functions are stored elsewhere. Cout <"Size of a non-virtual function class A2:" <sizeof (A2) <Endl; cout <"A2's virtual function table address: "<(int *) (& A2) <Endl; cout <" Address of the 1st functions in the A2 virtual function table: "<(int *) * (int *) (& A2) <Endl; // this class has no virtual function table because no virtual function exists, therefore, an error occurs when using the following statement (the value at the unknown // address is obtained ). // (Voidfun) * (int *) (& A2) (); cout <Endl; // class A3 A3 with one virtual member function; // because of the virtual member function, one virtual function table address Member is added with a size of 4. Cout <"size of class A3 with 1 virtual function:" <sizeof (A3) <Endl; cout <"A3's virtual function table address: "<(int *) (& A3) <Endl; pvtable = (INT **) & A3; cout <" Address of the 1st functions in the A3 virtual function table: "<& pvtable [0] [0] <Endl; (voidfun) pvtable [0] [0]) (); // cout <"the address of the 2nd functions in the A3 virtual function table:" <& pvtable [0] [1] <Endl; // The call fails. // (Voidfun) pvtable [0] [1]) (); the last element of the cout <"A3 virtual function table is: "<pvtable [0] [1] <Endl; // as shown in the preceding figure, what is the content of the last element of the virtual function table? Why is it not 0? Cout <Endl; // class A4 A4 with two virtual member functions; // size or 4 cout <"class A4 with two virtual functions: "<sizeof (A4) <Endl; cout <" A4 virtual function table address: "<(int *) (& A4) <Endl; pvtable = (INT **) & A4; cout <"Address of the 1st functions in the A4 virtual function table:" <& pvtable [0] [0] <Endl; (voidfun) pvtable [0] [0]) (); Address of the 2nd functions in the cout <"A4 virtual function table: "<& pvtable [0] [1] <Endl; (voidfun) pvtable [0] [1]) (); cout <"the last element of the A4 virtual function table is:" <pvtable [0] [2] <Endl; // It is found from the above that the virtual function is really a table and is based on the class In the virtual function declaration sequence. Cout <Endl; // single inheritance, does not cover the A5 A5; cout <"single inheritance, does not cover the A5 size of the base class virtual function: "<sizeof (A5) <Endl; cout <" A5 virtual function table address: "<(int *) (& A5) <Endl; pvtable = (INT **) & A5; cout <"Address of the 1st functions in the A5 virtual function table:" <& pvtable [0] [0] <Endl; (voidfun) pvtable [0] [0]) (); Address of the 2nd functions in the virtual function table of cout <"A5: "<& pvtable [0] [1] <Endl; (voidfun) pvtable [0] [1]) (); cout <"the last element of the A5 virtual function table is:" <pvtable [0] [2] <Endl; // from the virtual function table that is sent to the derived class, the virtual function of the base class is derived Class virtual function front cout <Endl; // single inheritance Level 3, does not cover the base class virtual function A51 A51; cout <"single inheritance Level 3, the size of class A51 does not cover the basic class virtual functions: "<sizeof (A51) <Endl; cout <" A51 virtual function table address: "<(int *) (& A51) <Endl; pvtable = (INT **) & A51; cout <" Address of the 1st functions in the A51 virtual function table: "<& pvtable [0] [0] <Endl; (voidfun) pvtable [0] [0]) (); cout <"Address of the 2nd functions in the virtual function table of A51:" <& pvtable [0] [1] <Endl; (voidfun) pvtable [0] [1]) (); cout <"Address of the 3rd functions in the virtual function table of A51: "<& pvtable [0] [2] <Endl; (voi Dfun) pvtable [0] [2]) (); cout <"the content of the last element of the virtual function table of A51 is: "<pvtable [0] [3] <Endl; // The virtual function table from the derived class, the virtual function of the base class is cout <Endl; // a single inheritance before the virtual function of the derived class, covering the base class virtual function A6 A6; cout <"single inheritance, the size of the A6 class that overrides the base-class virtual functions: "<sizeof (A6) <Endl; cout <" A6's virtual function table address: "<(int *) (& A6) <Endl; pvtable = (INT **) & A6; Address of the 1st functions in the cout <"A6 virtual function table: "<& pvtable [0] [0] <Endl; (voidfun) pvtable [0] [0]) (); cout <"A6 address of the 2nd functions in the virtual function table:" <& pvtable [0] [1] <End L; (voidfun) pvtable [0] [1]) (); the last element of the virtual function table of cout <"A6 is: "<pvtable [0] [2] <Endl; // a derived class overwrites the virtual function of the base class to replace the location of the base class's virtual function cout <Endl; // multi-inheritance, without overwriting the basic class virtual function A7 A7; // because two classes are inherited, there are two virtual function tables, so the size is 8. Cout <"Multi-inheritance, does not overwrite the A7 size of the class of the base class virtual function:" <sizeof (A7) <Endl; cout <"A7 virtual function table address:" <(int *) (& A7) <Endl; pvtable = (INT **) & A7; cout <"A7 virtual function table 1's 1st function addresses:" <& pvtable [0] [0] <Endl; (voidfun) pvtable [0] [0]) (); the address of the 2nd functions in the virtual function table 1 of cout <"A7: "<& pvtable [0] [1] <Endl; (voidfun) pvtable [0] [1]) (); cout <"A7 virtual function table 1's 3rd function addresses:" <& pvtable [0] [2] <Endl; (voidfun) pvtable [0] [2]) (); the content of the last element of cout <"A7's virtual function table 1 is :" <Pvtable [0] [3] <Endl; cout <"A7 virtual function table 2 contains the addresses of the 1st functions: "<& pvtable [1] [0] <Endl; (voidfun) pvtable [1] [0]) (); cout <"the address of the 2nd functions in table 2 of the A7 virtual function:" <& pvtable [1] [1] <Endl; (voidfun) pvtable [1] [1]) (); the last element of cout <"A7's virtual function table 2 is: "<pvtable [1] [2] <Endl; // It is found that the derived class inherits several classes with virtual functions, and there are several virtual function tables. // The sequence of the table is the same as the declaration it inherits. // Place the virtual function of the derived class in the virtual function table corresponding to its first parent class. Cout <Endl; // multi-inheritance, covering the A8 A8 of the basic class virtual function; // because the two classes are inherited, there are two virtual function tables, so the size is 8. Cout <"Multi-inheritance, covering the A8 size of the base class virtual function:" <sizeof (A8) <Endl; cout <"A8 virtual function table address: "<(int *) (& A8) <Endl; pvtable = (INT **) & A8; cout <"A8 virtual function table 1's 1st function addresses:" <& pvtable [0] [0] <Endl; (voidfun) pvtable [0] [0]) (); cout <"A8 virtual function Table 1 contains the address of the 2nd functions: "<& pvtable [0] [1] <Endl; (voidfun) pvtable [0] [1]) (); cout <"A8 virtual function table 1's 3rd function addresses:" <& pvtable [0] [2] <Endl; (voidfun) pvtable [0] [2]) (); the content of the last element of cout <"A8's virtual function table 1 is:" <<Pvtable [0] [3] <Endl; cout <"A8 virtual function table 2 contains the address of the 1st functions: "<& pvtable [1] [0] <Endl; (voidfun) pvtable [1] [0]) (); cout <"A8 virtual function table 2's 2nd function addresses:" <& pvtable [1] [1] <Endl; (voidfun) pvtable [1] [1]) (); the last element of cout <"A8's virtual function table 2 is: "<pvtable [1] [2] <Endl; // It is found that all the virtual functions that the derived class overwrites the base class are stored in Table 1 of the virtual function, place them in the declared inheritance order. Cout <Endl; return 0;}/* does not copy the result. Analyze the results by yourself based on the main program. */