C++虚函数和多态超详细分析

#include<iostream>
#include<string>
using namespace std;
class MM
{
public:
	//虚函数指针是同一个，所以无论该类中有多少个虚函数，
	//占用的内存就只是一个指针的大小
	virtual void print()
	{
		cout << "我是第一个虚函数" << endl;
	}
	virtual void printData() 
	{
		cout << "我是第二个虚函数" << endl;
	}
protected:
};
class son:public MM
{
public:
	void print() 
	{
		//该函数也是虚函数，
        //父类中同名函数是虚函数
		//所以子类该函数也是虚函数
	}
protected:
};
int main() 
{
	cout << sizeof(MM) << endl;
	cout << "...................." << endl;
	//虚函数表的理解，下面带图解
	MM mm;
	long long** p = (long long**)&mm;
	using Func = void(*)();
	Func f1 = (Func)p[0][0];
	Func f2 = (Func)p[0][1];
	f1();
	f2();
	return 0;
}

#include<iostream>
using namespace std;
class MM
{
public:
	virtual void print() = 0;
};
int main()
{
	//MM mm; //抽象类不能构建对象
	MM* pmm = nullptr;
	return 0;
}

#include<iostream>
using namespace std;
class MM
{
public:
	void print()
	{
		cout << "父类" << endl;
	}
	virtual void printData()
	{
		cout << "MM" << endl;
	}
};
class son :public MM 
{
public:
	void print() 
	{
		cout << "子类" << endl;
	}
	void printData() 
	{
		cout << "son" << endl;
	}
};
int main()
{
	MM* pmm = new son;
	pmm->print();
	pmm->printData();
	return 0;
}

#include<iostream>
#include<string>
using namespace std;
class data
{
public:
	string name;
	int age;
};
class MM
{
public:
	virtual bool empty() = 0;
	virtual int size() = 0;
};
class List:public MM
{
public:
	bool empty()
	{
		return 0;
	}
	int size()
	{
		return NULL;
	}
};
int main()
{
	MM* pmm = new List;
	pmm->empty();
	pmm->size();
}

#include<iostream>
using namespace std;
class MM
{
public:
	virtual ~MM()
	{
		cout << "父类" << endl;
	}
};
class son:public MM
{
public:
	~son()
	{
		cout << "子类" << endl;
	}
};
int main()
{
	MM* pmm = new son;
	delete pmm;
	return 0;
}

#include<iostream>
using namespace std;
class MM
{
public:
	virtual void print() { cout << "MM" << endl; }
};
class son:public MM
{
public:
	void print() { cout << "son" << endl; }
};
class A
{
public:
	virtual void print(){}
};
class B
{
public:
	virtual void print() {}
};
class C:public A,public B
{
public:
	void print()
	{
		cout << "c" << endl;
	}
};
int main()
{
	MM* partent = new MM;
	son* Son = new son;
	//上行转换----->没有必要
	MM* p = static_cast<MM*>(Son);
	MM* pp = dynamic_cast<MM*>(Son);
	MM* ppp = Son;       //可以
	//下行转换
	son* x = dynamic_cast<son*>(partent); //安全，父类没有virtual会报错---->多态
	if(!x)
	{
		printf("error");
	}                           //下行转换不安全，不会申请成功
	A* a = new A;
	B* b = dynamic_cast<B*>(a);
	b->print();
	return 0;
}

#include<iostream>
#include<functional>
using namespace std;
class MM
{
public:
	void print() { cout << "king" << endl; }
	static void printData() { cout << "MM" << endl; }
};
int main()
{
	void(*p)() = &MM::printData;
	p();
	//必须通过对象调用
	void(MM::*pp)() = &MM::print;
	MM mm;
	(mm.*pp)();
	//函数适配器，让函数调用形态可以适用于别的形态
	auto f = bind(&MM::print, &mm);
	f();
	return 0;
}