C++基类与派生类的函数调用情况

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在定义了基类的指针与派生类的对象，或者是派生类指针与基类的对象。

在函数调用的时候，如果该函数在基类中被定义为虚函数，那么在调用的时候看该指针（包括基类指针和派生类指针）所指向的对象，如果是派生类的对象就调用派生类中重写的函数，如果是基类的对象就调用基类中的函数。如果该函数为非虚函数，那么看该指针的类型，如果是基类的指针就调用基类中的函数，如果是派生类的指针就调用派生类中的函数。这种情况是非多态的情况，函数没有实现重写，而只是进行了覆盖。

#include "iostream"  using namespace std;    #include<iostream>  using namespace std;    class Base  {  public:      virtual void f(float x)      {          cout<<"Base::f(float)"<< x <<endl;      }      void g(float x)      {          cout<<"Base::g(float)"<< x <<endl;      }  };    class Derived : public Base  {  public:      virtual void f(float x)      {          cout<<"Derived::f(float)"<< x <<endl;   //多态、覆盖      }      void g(int x)      {          cout<<"Derived::g(int)"<< x <<endl;     //隐藏      }  };    int main(void)  {      //定义子类的对象      Derived d;      // 基类的指针指向子类对象      Base *pb = &d;      //子类指针指向子类对象      Derived *pd = &d;        //虚函数，是调用所指向对象的函数      pb->f(3.14f);   // Derived::f(float) 3.14      pd->f(3.14f);   // Derived::f(float) 3.14        // 非虚函数，根据指针属于基类或子类调用      pb->g(3.14f);   // Base::g(float)  3.14      pd->g(3.14f);   // Derived::g(int) 3         Base a;//定义基类的对象      Derived *ptr = (Derived *)&a;//子类的指针        ptr->f(3.14f);  // Base::f(float)  3.14      ptr->g(3.14f); // Derived::g(int) 3         return 0;  }

#include <iostream>using namespace std;class Contained1 {public:Contained1() {cout << "Contained1 constructor." << endl;}~Contained1(){cout << "Contained1 destructor." << endl;}};class Contained2 {public:Contained2() {cout << "Contained2 constructor." << endl;}~Contained2(){cout << "Contained2 destructor." << endl;}};class Contained3 {public:Contained3() {cout << "Contained3 constructor." << endl;}~Contained3(){cout << "Contained3 destructor." << endl;}};class BaseContainer {public:BaseContainer() {cout << "BaseContainer constructor." << endl;}// virtual destructor is very important here, or will cause resources leak.virtual ~BaseContainer(){cout << "BaseContainer destructor." << endl;}private:Contained1 c1;Contained2 c2;};class DerivedContainer : public BaseContainer {public:DerivedContainer(){cout << "DerivedContainer constructor." << endl;}~DerivedContainer(){cout << "DerivedContainer destructor." << endl;}private:Contained3 c3;};int main() {DerivedContainer dc;cout << "+++++++++++++" << endl;BaseContainer *p = new DerivedContainer();cout << "*************" << endl;/** If baseContainer destructor is not virtual, delete p has undefined behaviour.* In most implementations, the call to the destructor will be resolved like any non-virtual code,* meaning that the destructor of the base class will be called but not the one of the derived class,* resulting in a resources leak.* Refer to:* http://stackoverflow.com/questions/461203/when-to-use-virtual-destructors*/delete p;cout << "-------------" << endl;return 0;// Here dc is destroyed normally no matter whether the base class's destructor is virtual or not.}

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