Computer _ virtual function table memory distribution (Chen Hao's)

Original article link: Workshop. Lab

Class base {public: Virtual void F () {cout <"base: F ()" <Endl;} virtual void g () {cout <"base :: G () "<Endl;} virtual void H () {cout <" base: H () "<Endl;} protected: Private :}; class base2 {public: Virtual void F () {cout <"base2: F ()" <Endl;} virtual void g () {cout <"base2 :: G () "<Endl;} virtual void H () {cout <" base2: H () "<Endl;} protected: Private :}; // No overwrite. In this case, the virtual function will append the original virtual function table to the class derived: public base {public: Virtual void F1 () {cout <"derived: F1 ()" <Endl;} virtual void G1 () {cout <"derived: G1 ()" <Endl ;} virtual void H1 () {cout <"derived: H1 ()" <Endl ;}; // if so, the same function overwrites class derived_cover: public base {public: Virtual void F () {cout <"derived_cover: F ()" <Endl;} virtual void G1 () {cout <"derived_cover :: g1 () "<Endl ;}virtual void H1 () {cout <" derived_cover: H1 () "<Endl ;}; // multiple inheritance, no overwrite class multiplederived: public base, public base2 {public: Virtual void F1 () {cout <"multiplederived: F1 ()" <Endl;} virtual void G1 () {cout <"multiplederived: G1 ()" <Endl ;}; // multi-inheritance, with overwrite class multiplederivedcover: public base, public base2 {public: virtual void F () {cout <"multiplederivedcover: F ()" <Endl;} virtual void G1 () {cout <"multiplederivedcover: G1 () "<Endl ;}}; typedef void (* Fun) (void); // test the storage relationship between the virtual function and the virtual function table void test1 () {Base B; fun pfun = NULL; cout <"virtual function table address" <(int *) * (int *) (& B) <Endl; cout <"first function address of the virtual function table" <(int *) * (int *) (& B) <Endl; cout <"virtual function table second function address" <(int *) * (int *) (& B) + 1) <Endl; cout <"virtual function table third function address" <(int *) * (int *) (& B) + 2) <Endl; // directly access the function content in the virtual function table through the pointer pfun = (fun) (int *) * (int *) (& B ); pfun (); pfun = (fun) (int *) * (int *) (& B) + 1); pfun (); pfun = (fun) (int *) * (int *) (& B) + 2); pfun ();} // if the test does not cover the function, add void Test2 () {Base B; derived derive; fun pfun = NULL to the end of the original virtual function table; cout <"virtual function table address" <(int *) * (int *) (& B) <Endl; cout <"virtual function table address" <(int *) * (int *) (& derive) <Endl; cout <"first function address of the virtual function table" <(int *) * (int *) (& B) <Endl; cout <"first function address of the virtual function table" <(int *) * (int *) (& derive) <Endl; cout <"virtual function table second function address" <(int *) * (int *) (& B) + 1) <Endl; cout <"virtual function table second function address" <(int *) * (int *) (& derive) + 1) <Endl; cout <"virtual function table third function address" <(int *) * (int *) (& B) + 2) <Endl; cout <"virtual function table third function address" <(int *) * (int *) (& derive) + 2) <Endl; // print out the virtual function content pfun = (fun) (int *) * (int *) (& derive); pfun (); pfun = (fun) (int *) * (int *) (& derive) + 1); pfun (); pfun = (fun) (int *) * (int *) (& derive) + 2); pfun (); pfun = (fun) (int *) * (int *) * (int *) (& derive) + 3); pfun (); pfun = (fun) (int *) * (int *) (& derive) + 4); pfun (); pfun = (fun) (int *) * (int *) (& derive) + 5 ); pfun ();} // overwrite the original function, and the void test3 () {Base B; derived_cover derive; fun pfun = NULL; cout <"virtual function table address" <(int *) * (int *) (& B) <Endl; cout <"virtual function table address" <(int *) * (int *) (& derive) <Endl; cout <"first function address of the virtual function table" <(int *) * (int *) (& B) <Endl; cout <"first function address of the virtual function table" <(int *) * (int *) (& derive) <Endl; cout <"virtual function table second function address" <(int *) * (int *) (& B) + 1) <Endl; cout <"virtual function table second function address" <(int *) * (int *) (& derive) + 1) <Endl; cout <"virtual function table third function address" <(int *) * (int *) (& B) + 2) <Endl; cout <"virtual function table third function address" <(int *) * (int *) (& derive) + 2) <Endl; // print out the virtual function content pfun = (fun) (int *) * (int *) (& derive ); // F overwrites F of the parent class pfun (); pfun = (fun) (int *) * (int *) (& derive) + 1); pfun (); pfun = (fun) (int *) * (int *) (& derive) + 2); pfun (); pfun = (fun) (int *) * (int *) (& derive) + 3); // pfun (); pfun = (fun) (int *) * (int *) (& derive) + 4); pfun (); cout <"if the function implemented by the subclass is called directly through the parent class Pointer" <Endl; base * newbase = new derived_cover; newbase-> F (); newbase-> G (); newbase-> H ();} // test the Memory Distribution of the Multi-inherited virtual function table, there should be two virtual function tables, // pointing to base and base2 respectively, without overwriting void test4 () {cout <"Multi-inheritance Memory Distribution" <Endl; multiplederived mymultiple; fun pfun = NULL; cout <"Multi-inherited virtual function 1 Address" <(int *) * (int *) (& mymultiple) <Endl; cout <"Multi-inherited virtual function 2 address" <(int *) * (int *) (& mymultiple) + 1) <Endl; cout <"virtual function table 1 should be a function not covered by base function + subclass" <Endl; pfun = (fun) (int *) * (int *) * (int *) (& mymultiple); // fun1 base: F () pfun (); pfun = (fun) (int *) * (int *) * (int *) (& mymultiple) + 1); // The fun2 base of the ALI group: G () pfun (); pfun = (fun) (int *) * (int *) (& mymultiple) + 2); // fun3 base: H () pfun (); pfun = (fun) (int *) * (int *) (& mymultiple) + 3); // fun4 multiplederived: F1 () pfun (); pfun = (fun) (int *) * (int *) (& mymultiple) + 4); // fun4 multiplederived: G1 () pfun (); cout <"virtual function table 2" <Endl; pfun = (fun) (int *) * (int *) (& mymultiple) + 1); pfun (); pfun = (fun) (int *) * (int *) (& mymultiple) + 1) + 1); pfun () ;}// test that multiple inheritance types include void test5 () {cout <"multiple inheritance types include override" <Endl; multiplederivedcover D; base * D1 = & D; base2 * D2 = & D; D1-> F (); D2-> F (); D1-> G (); d2-> G () ;}int main () {test1 (); Test2 (); test3 (); test4 (); test5 (); Return 0 ;}