C++继承的赋值转换与菱形虚拟继承深入详解

class person{
protected:
	string _name;
	int _age;
};
class student :public person
{
public:
	int _No;
};
void test01()
{
	student sobj;
	//1.子类对象可以赋值给父类对象/指针/引用
	person pobj = sobj;
	person* pp = &sobj;
	person& rp = sobj;
	//2.基类对象不可以赋值给派生类对象
	//sobj = pobj;
	//3.基类的指针可以通过强制类型转换赋值给派生类的指针
	pp = &sobj;
	student* ps1 = (student*)pp;//这种情况是可以的
	ps1->_No = 10;
	pp = &pobj;
	student* ps2 = (student*)pp;//这种情况转换时虽然可以，但存在越界访问的问题
	ps2->_No = 10;
}

class Base {
public:
	Base(){
		m_A = 100;
	}
	void func(){
		cout << "Base - func()调用" << endl;
	}
	void func(int a){
		cout << "Base - func(int a)调用" << endl;
	}
public:
	int m_A;
};
class Son : public Base {
public:
	Son(){
		m_A = 200;
	}
	//当子类与父类拥有同名的成员函数，子类会隐藏父类中所有版本的同名成员函数
	//如果想访问父类中被隐藏的同名成员函数，需要加父类的作用域
	void func()
	{
		cout << "Son - func()调用" << endl;
	}
public:
	int m_A;
};
void test01()
{
	Son s;
	cout << "Son下的m_A = " << s.m_A << endl;
	cout << "Base下的m_A = " << s.Base::m_A << endl;
	s.func();
	s.Base::func();
	s.Base::func(10);
}

class Base {
public:
	static void func()
	{
		cout << "Base - static void func()" << endl;
	}
	static void func(int a)
	{
		cout << "Base - static void func(int a)" << endl;
	}
	static int m_A;
};
int Base::m_A = 100;
class Son : public Base {
public:
	static void func()
	{
		cout << "Son - static void func()" << endl;
	}
	static int m_A;
};
int Son::m_A = 200;
//同名成员属性
void test01()
{
	//通过对象访问
	cout << "通过对象访问： " << endl;
	Son s;
	cout << "Son  下 m_A = " << s.m_A << endl;
	cout << "Base 下 m_A = " << s.Base::m_A << endl;
	//通过类名访问
	cout << "通过类名访问： " << endl;
	cout << "Son  下 m_A = " << Son::m_A << endl;
	cout << "Base 下 m_A = " << Son::Base::m_A << endl;
}
//同名成员函数
void test02()
{
	//通过对象访问
	cout << "通过对象访问： " << endl;
	Son s;
	s.func();
	s.Base::func();
	cout << "通过类名访问： " << endl;
	Son::func();
	Son::Base::func();
	//出现同名，子类会隐藏掉父类中所有同名成员函数，需要加作作用域访问
	Son::Base::func(100);
}

class person
{
public:
	person()
	{
		_count++;
	}
protected:
	string _name;
public:
	static int _count;//统计人数
};
int person::_count = 0;
class student:public person
{
protected:
	int _stuNum;
};
class graduate :public student
{
protected:
	string course;
};
void test()
{
	student s1;
	student s2;
	student s3;
	graduate s4;
	cout << "人数" << person::_count << endl;
	student::_count = 0;
	cout << "人数" << person::_count << endl;
}

class person
{
public:
	person(const char* name = "pxl")
		:_name(name)
	{}
	person(const person& p)
		:_name(p._name)
	{}
	person& operator=(const person& p)
	{
		if (this != *p){
			_name = p._name;
		}
		return *this;
	}
	~person()
	{}
protected:
	string _name;
};
class student :public person
{
public:
	student(const char* name, int num)
		:person(name)//显示调用基类的构造函数初始化基类成员
		, _num(num)
	{}
	student(const student& s)
		:person(s)//注意这里有个隐式的切片操作 person& p = s;
		, _num(s._num)
	{}
	student& operator=(const student& s)
	{
		if (this != &s){
			person::operator=(s);//调用基类的operator=完成基类的赋值
			_num = s._num;
		}
		return *this;
	}
	~student()
	{
		cout << "~student()" << endl;
		//注意这里会自动调用父类析构
	}
protected:
	int _num;
};
void test()
{
	student s1("ppp", 20);
	student s2(s1);
	student s3("xxx", 30);
	s1 = s3;
}

class A{
public:
	int _a;
};
class B:public A
{
public:
	int _b;
};
class C :public A
{
public:
	int _c;
};
class D :public B, public C
{
public:
	int _d;
};
int main()
{
	D d;
	d.B::_a = 1;
	d.C::_a = 2;
	d._b = 3;
	d._c = 4;
	d._d = 5;
	system("pause");
	return 0;
}