Unit 13Polymophism Virtual Functions课件.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Calls up the chain You can still call the overridden function: void Derived::func() { cout In Derived::func!; Base::func(); // call to base class } This is a common way to add new functionality No need to copy the old stuff! * Overloading and virtuals Overloading adds multiple signatures class Base { public: virtual void func(); virtual void func(int); }; If you override an overloaded function, you must override all of the variants! Cant override just one If you dont override all, some will be hidden * overloading overriding #//virtual functions restrict overloading #include iostream #include string using namespace std; class Base{ public: virtual int f() const{ coutBase::int f()\n; return 1; } virtual void f(string) const {coutBase::void f(string)\n; } virtual void g() const{} }; class Derived1:public Base{ public: void g() const{} }; class Derived2:public Base{ public: int f() const{ coutDerived2::int f()\n; return 2; } }; class Derived3:public Base{ public: void f() const{ coutDerived3::void f()\n;} }; class Derived4:public Base{ public: int f(int) const{ coutDerived4::int f(int)\n; return 4; } }; Just change return type * #//virtual functions restrict overloading #include iostream #include string using namespace std; class Base{ public: virtual int f() const{ coutBase::int f()\n; return 1; } virtual void f(string) const {coutBase::void f(string)\n; } virtual void g() const{} }; class Derived1:public Base{ public: void g() const{} }; class Derived2:public Base{ public: int f() const{ coutDerived2::int f()\n; return 2; } }; class Derived3:public Base{ public: void f(int) const{coutDerived3::void f(int)\n;} }; class Derived4:public Base{ public: int f(int) const{ coutDerived4::int f(int)\n; return 4; } }; void main(){ string s(hello); Derived1 d1; int x=d1.f(); d1.f(s); Derived2 d2; x=d2.f(); //!d2.f(s); Derived3 d3; d3.f(1); //!x=d3.f(); //!d3.f(s);