虚函数问题 | 易学教程

虚函数多态（装箱调用）只能通过指针和引用实现

#include<iostream>
#include<windows.h>
using namespace std;
class A {
public:
 A() { cout << "Constructing class A\n"; }
 virtual void m() { cout << "invoking f from class A.\n"; }
};
class B : public A {
public:
 B() { cout << "Constructing class B\n"; }
  void m() { cout << "invoking f from class B.\n"; }
};
class C :public B {
public:
 C() { cout << "Constructing class C\n"; }
     void m() { cout << "invoking f from class C.\n"; }
};
class D :public C {
public:
 D() { cout << "Constructing class D\n"; }
 void m() { cout << "invoking f from class D.\n"; }
};
void p(A &a)
{
 a.m();
}
int main()
{
 D d;
 p(d);
 system("pause");
 return 0;
}

例如这里的p()，函数，主函数把D的对象d作为参数传进p()中，在里面调用m（）函数。因为m（）为虚函数，所以结果如下：
运行结果
2.
普通象是会创建基类对象的拷贝
子类那部分没了所以子类的虚函数重写也没了
例如：

#include<iostream>
#include<windows.h>
using namespace std;
class A {
public:
 A() { cout << "Constructing class A\n"; }
 virtual void m() { cout << "invoking f from class A.\n"; }
};
class B : public A {
public:
 B() { cout << "Constructing class B\n"; }
  void m() { cout << "invoking f from class B.\n"; }
};
class C :public B {
public:
 C() { cout << "Constructing class C\n"; }
     void m() { cout << "invoking f from class C.\n"; }
};
class D :public C {
public:
 D() { cout << "Constructing class D\n"; }
 void m() { cout << "invoking f from class D.\n"; }
};
void p(A a)
{
 a.m();
}
int main()
{
 D d;
 p(d);
 system("pause");
 return 0;
}

运行结果如下：

来源：CSDN

作者：金色飞贼.

链接：https://blog.csdn.net/qq_43593646/article/details/103643309

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虚函数