C++允许用户将使用虚拟函数的运行时多态性的概念用于任何类型的Inheritance。
以下是在所有类型的继承中如何实现运行时多态的方法：
- 单一继承：
// C++ program to demonstrate Run Time // Polymorphism in Single Inheritance #includeusing namespace std; // Base Class class Base { public: // Virtual function virtual void funct1() { cout << "Base::funct1() is called\n"; } // Virtual function virtual void funct2(int x) { cout << "Base's Val of x:" << x << endl; } // Non-Virtual Function void funct3() { cout << "Base is the Parent class!" << endl; } }; // Derived Class or Sub Class class Derived : public Base { private: // Virtual Functions // can also be Private! void funct1() { cout << "Derived::funct1() is called\n"; } void funct2(int x) { cout << "Derived Class's Val of x:" << x << endl; } void funct3() { cout << "It's the Derived class's" << " funct3() called!" << endl; } }; int main() { // Run-Time Polymorphism // in Single Inheritance Base* bptr = new Derived(); // virtual function bptr->funct1(); // virtual function bptr->funct2(12); // Non-virtual function bptr->funct3(); return 0; } 输出：Derived::funct1() is called Derived Class's Val of x:12 Base is the Parent class! - 多重继承：
#includeusing namespace std; // Parent to Derived class class Base1 { public: // Non-Virtual function void funct1() { cout << "Base1::funct1() is called\n"; } // Virtual function virtual void funct2(int x) { cout << "Base1's Val of x:" << x << endl; } // Non-Virtual Function void funct3() { cout << "Base1 is the Parent class!" << endl; } }; // Second Parent to Derived class class Base2 { public: void funct1() { cout << "Base2::funct1() is called\n"; } void funct2(int x) { cout << "Base2's Val of x:" << x << endl; } // Only Virtual Function // in Base2 Parent class virtual void funct3() { cout << "Base2 is Also a Parent class!" << endl; } }; // Derived Class of Base1 and Base2 class Derived : public Base1, public Base2 { private: void funct1() { cout << "Derived::funct1() is called\n"; } void funct2(int x) { cout << "Derived Class's Val of x:" << x << endl; } void funct3() { cout << "Derived::funct3() is called " << "and not Base2::funct3() due" << " to RTP" << endl; } }; int main() { Derived d; // Run-Time Polymorphism // in Multiple Inheritance Base1* b1ptr = &d; // Compile-Time Binding, // Hence Base1::funct1() will be called! b1ptr->funct1(); // virtual function of Base1 // RunTime PolyMorphism b1ptr->funct2(10); // Now Parent Class Base2 // is also pointed to object 'd' // of Derived (to demonstrate RTP) Base2* b2ptr = &d; // virtual function of Base2 // RunTime PolyMorphism b2ptr->funct3(); return 0; } 输出：Base1::funct1() is called Derived Class's Val of x:10 Derived::funct3() is called and not Base2::funct3() due to RTP注意：此处Base1指针和Base2指针都可能指向相同的派生类对象d，但实际上，由于使用了不同的基类指针，编译器在运行时选择了不同的虚函数。
- 多级继承：
// C++ Program to illustrate Run-Time // Polymorphism in multi-level inheritance #includeusing namespace std; // Parent Class class Base1 { public: // Virtual function virtual void funct1() { cout << "Base1::funct1() is called\n"; } // Virtual function virtual void funct2(int x) { cout << "Base1's Val of x:" << x << endl; } // Non-Virtual Function void funct3() { cout << "Base1 is the Parent class!" << endl; } }; // Derived Class of Base1 // but Parent to Base3 class Base2 : public Base1 { // Virtual Functions can be Private! private: void funct1() { cout << "Base2::funct1() is called\n"; } void funct2(int x) { cout << "Base2's Val of x:" << x << endl; } void funct3() { cout << "Base2 is the first " << "Derived class!" << endl; } }; // Derived Class of Base2 // but Parent to Derived class Base3 : public Base2 { private: void funct1() { cout << "Base3::funct1() is called\n"; } void funct2(int x) { cout << "Base3's Val of x:" << x << endl; } void funct3() { cout << "Class Base3 is second " << "Derived class!" << endl; } }; // 3 Levels of Multi-Level Inheritance // and final Child Class class Derived : public Base3 { private: void funct1() { cout << "Derived::funct1() is called\n"; } void funct2(int x) { cout << "Derived Class's Val of x:" << x << endl; } void funct3() { cout << "Class Derived is Final" << " Child class!" << endl; } }; int main() { // Run-Time Polymorphism // in multi-level Inheritance Base1* b1ptr = new Derived; b1ptr->funct1(); b1ptr->funct2(30); // Compile-Time Binding b1ptr->funct3(); return 0; } 输出：Derived::funct1() is called Derived Class's Val of x:30 Base1 is the Parent class!说明：在上面的示例中，Derived类是继承自Base3的最终子类，该子类继承自Base2，后者又再次继承自Base1(父类为Base2)。但是，即使您尝试在Base1类中使用虚拟函数并将其指针指向派生类(这是Base1的曾祖父)，也可以看到运行时多态性。因此，即使在这里，运行时多态也可以根据标准规则进行工作。
- 层次继承：
// C++ Program to illustrate Run-Time // Polymorphism in Hierarchical inheritance #includeusing namespace std; class Base1 { public: // Virtual function of Parent Class virtual void funct1() { cout << "Base1::funct1() is called\n"; } virtual void funct2(int x) { cout << "Base1's Val of x:" << x << endl; } // Non-Virtual Function void funct3() { cout << "Base1 is the Parent class!" << endl; } }; class Base2 : public Base1 { private: void funct1() { cout << "Base2::funct1() is called\n"; } void funct2(int x) { cout << "Base2's Val of x:" << x << endl; } void funct3() { cout << "Base2 is the first" << " Derived class!" << endl; } }; class Base3 : public Base1 { private: void funct1() { cout << "Base3::funct1() is called\n"; } void funct2(int x) { cout << "Base3's Val of x:" << x << endl; } void funct3() { cout << "Class Base3 is second" << " Derived class!" << endl; } }; // Grand-Child_1 of Base1 class class Derived1 : public Base3 { private: void funct1() { cout << "Derived1::funct1() is called\n"; } void funct2(int x) { cout << "Derived1 Class's Val of x:" << x << endl; } void funct3() { cout << "Class Derived1 is Good!!" << endl; } }; // Grand-Child_2 of Base1 class class Derived2 : public Base3 { private: void funct1() { cout << "Derived2::funct1()" << " is called\n"; } void funct2(int x) { cout << "Derived2 Class's Val " << "of x:" << x << endl; } void funct3() { cout << "Class Derived2 is Good!!" << endl; } }; // Run-Time Polymorphism // in Hierarchical Inheritance int main() { // Base1 class's(Parent class's) // pointer points to Derived1 class Base1* b1ptr = new Derived1(); // Run-Time Polymorphism b1ptr->funct1(); Derived2 d2; // Now the Base1 class pointer // points to d2 object(Derived2 class) b1ptr = &d2; // Run-Time Polymorphism b1ptr->funct2(30); // Compile-Time Binding b1ptr->funct3(); return 0; } 输出：Derived1::funct1() is called Derived2 Class's Val of x:30 Base1 is the Parent class!说明：在这里，父级是Base1，其子级是Derived1类和Derived2类。即使在这种情况下，由于虚拟功能(“ VPTR”和“ VTABLE”)，当将Base1类指针指向Derived1对象或Derived2对象时，我们也可以在此处应用运行时多态。
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