类型兼容性的解决心方法

待我称王封你为后i 2022-06-07 22:55 125阅读 0赞

#include <iostream>
    using namespace std;
    class parent{
    public:
    	parent(int a)
    	{
    		this->va = a;
    	}
    	virtual void print(void)
    	{
    		cout << "基类的a" <<this->va<< endl;
    	}
    private:
    	int va;
    };
    class child : public parent{
    public:
    	child(int a) : parent(100)
    	{
    		this->a = a;
    	}
    	virtual void print(void)
    	{
    		cout << "派生类的a" <<this->a<< endl;
    	}
    private:
    	int a;
    };
    int main()
    {
    	child oop(10);
    	parent oop1(20);
    	parent* p = NULL;
    	p = &oop;
    	p = &oop1;
    	parent &pt = oop;
    	p->print();
    	pt.print();
    	system("pause");
    	return 0;
    }

\* 父类指针可以直接指向子类对象

\* 父类引用可以直接指向子类对象

上述结论不管是父类指针还是引用指向子类对像，调用的print都是父类的print，这种解决办法是在print的实现前面加上virtual关键字

实例：

#include <iostream>
    using namespace std;
    class parent{
    public:
    	parent(int a)
    	{
    		this->va = a;
    	}
    	virtual void print(void)
    	{
    		cout << "基类的a" <<this->va<< endl;
    	}
    private:
    	int va;
    };
    class child : public parent{
    public:
    	child(int a) : parent(100)
    	{
    		this->a = a;
    	}
    	virtual void print(void)
    	{
    		cout << "派生类的a" <<this->a<< endl;
    	}
    private:
    	int a;
    };
    void test1(parent* p)
    {
    	p->print();
    }
    
    void test2(parent & pt)
    {
    	pt.print();
    }
    int main()
    {
    	child oop(10);
    	parent oop1(20);
    	parent* p = NULL;
    	p = &oop;
    	p = &oop1;
    	parent &pt = oop;
    	p->print();
    	pt.print();
    	test1(&oop);
    	test1(&oop1);
    	test2(oop);
    	test2(oop1);
    	system("pause");
    	return 0;
    }

这样就可执行到子类的print了，这里的virtual也可以只加载父类的virtual前，这也是一种多态的调用案例