查看“C++ 虚函数”的源代码

虚函数是应在派生类中重新定义的成员函数。 当使用指针或对基类的引用来引用派生的类对象时，可以为该对象调用虚函数并执行该函数的派生类版本。

如果声明的类不提供 PrintBalance 函数的重写实现，则使用基类 Account 中的默认实现。

可通过使用范围解析运算符 (::) 显式限定函数名称来禁用虚函数调用机制。


 #include <iostream>
 using namespace std;
 
 class Base {
 public:
 	virtual void NameOf();   // Virtual function.
 	void InvokingClass();   // Nonvirtual function.
 };
 
 // Implement the two functions.
 void Base::NameOf() {
 	cout << "Base::NameOf\n";
 }
 
 void Base::InvokingClass() {
 	cout << "Invoked by Base\n";
 }
 
 class Derived : public Base {
 public:
 	void NameOf();   // Virtual function.
 	void InvokingClass();   // Nonvirtual function.
 };
 
 // Implement the two functions.
 void Derived::NameOf() {
 	cout << "Derived::NameOf\n";
 }
 
 void Derived::InvokingClass() {
 	cout << "Invoked by Derived\n";
 }
 
 int main() {
 	// Declare an object of type Derived.
 	Derived aDerived;
 
 	// Declare two pointers, one of type Derived * and the other
 	//  of type Base *, and initialize them to point to aDerived.
 	Derived* pDerived = &aDerived;
 	Base* pBase = &aDerived;
 
 	// Call the functions.
 	pBase->NameOf();           // Call virtual function.
 	pBase->InvokingClass();    // Call nonvirtual function.
 	pBase->Base::NameOf();
 
 	pDerived->NameOf();        // Call virtual function.
 	pDerived->InvokingClass(); // Call nonvirtual function.
 }


 Derived::NameOf
 Invoked by Base
 Base::NameOf
 Derived::NameOf
 Invoked by Derived