老生常谈C++ 中的继承

#include <iostream>
#include <string>

using namespace std;

class Person
{
public:
	void Print()
	{
		cout << "name:" << _name << endl;
		cout << "age:" << _age << endl;
	}
protected:
	string _name = "peter"; // 姓名
	int _age = 18;
};
class Student : public Person
{
protected:
	int _stuid;
};
int main()
{
	Person p;
	Student s;
	p.Print();
	s.Print();
	return 0;
}

#include <iostream>
#include <string>
using namespace std;

class Person
{
public:
	    // 缺省
		string _name = "陈志浩"; // 姓名
		string _sex = "男"; // 性别
		int _age = 25; // 年龄
};
class Student : public Person
{
public:
	int _No = 2019124084; // 学号
};

void Test()
{
	Person pobj;
	Student sobj;
	// 修改子类的成员变量方便演示
	sobj._name = "chenzhiiao";
	sobj._age = 23;
}
int main()
{
	Test();
	return 0;
}

#include <iostream>
using namespace std;

class A {
public:
	void fun()
	{
		cout << "func()" << endl;
	}
};
class B : public A {
public:
	void fun(int i)
	{
		cout << "func(int i)->" << i << endl;
	}
};
void Test()
{
	// B中的fun和A中的fun不是构成重载，因为不是在同一作用域
	// B中的fun和A中的fun构成隐藏，成员函数满足函数名相同就构成隐藏。
	B b;
	b.fun(10);
	b.A::fun();//可以使用 基类::基类成员 显示访问
};
int main()
{
	Test();
	return 0;
}

#include <iostream>
#include <string>
#include <ostream>
using namespace std;
class Person
{
public:
	friend ostream& operator<<(ostream& out, const Person& p);
	Person(const char* name = "peter")
		: _name(name)
	{
		cout << "Person()" << endl;
	}

	Person(const Person& p)
		: _name(p._name)
	{
		cout << "Person(const Person& p)" << endl;
	}

	Person& operator=(const Person& p)
	{
		cout << "Person& operator=(const Person& p)" << endl;
		if (this != &p)
			_name = p._name;

		return *this;
	}

	~Person()
	{
		cout << "~Person()" << endl;
	}
protected:
	string _name; // 姓名
};
ostream& operator<<(ostream& out, const Person& p)
{
	out << "name : " << p._name << endl;
	return out;
}
class Student : public Person{
public:
	friend ostream& operator<<(ostream& out, const Student& s);
	Student(const char* name = "chenzhiao", int no = 2019)
		:Person(name)
		,_no(no)
	{
		cout << "Student()" << endl;
	}
	
	~Student()
	{
		cout << "~Student()" << endl;
	}

protected:
	int _no;
};
ostream& operator<<(ostream& out, const Student& s)
{
	out << "name : " << s._name << ",no : " << s._no << endl;
	return out;
}

void Test()
{
	Student s1;	
	cout << s1;
};
int main()
{
	Test();
	return 0;
}

Student(const Student& s)
		: Person(s), _no(s._no)
	{
		cout << "Student(const Student& s)" << endl;
	}

Student& operator=(const Student& s)
	{
		if (this != &s)
		{
			Person::operator=(s); 
			//这里必须要用类名指定，否则子类的operator=会把父类的
			//的operator=隐藏掉，导致无限递归调用子类的operator=导致栈溢出
			_no = s._no;
		}
		return *this;
	}

~Student()
	{
		cout << "~Student()" << endl;
		Person::~Person(); 
		//C++的编译器保证了这个代码默认会执行，但是必须要放在最后一行才符合规则
		//不能让程序员去手动指定Person::~Person();必须要放在最后一行
		//万一程序员不小心放在了第一行，会导致一些不可预料的错误，所以不要显示调用
		//这和上面3个默认成员的规则不一样，需要多注意
	}

#include <iostream>
#include <string>
using namespace std;

class Person
{
public:
	Person() { ++_count; }
protected:
	string _name; // 姓名
public:
	static int _count; // 统计人的个数。
};
int Person::_count = 0;
class Student : public Person
{
protected:
	int _stuNum; // 学号
};
class Graduate : public Student
{
protected:
	string _seminarCourse; // 研究科目
};
void TestPerson()
{
	Student s1;
	Student s2;
	Student s3;
	Graduate s4;
	Person s5;
	cout << " 人数 :" << Person::_count << endl;
	Student::_count = 0;
	cout << " 人数 :" << Person::_count << endl;
}
int main()
{
	TestPerson();
	return 0;
}

#include <iostream>
#include <string>
using namespace std;

class Person{
public:
	string _name;
};
class Student : public Person{
protected:
	int _stuId;
};
class Teacher : public Person{
protected:
	int _teaId;
};
class Assistant : public Student, public Teacher{
protected:
	string _majorCourse;
};
void Test()
{

	Assistant a;
	//a._name = "chenzhiao"; 这样会有二义性无法明确知道访问的是哪一个

	// 需要显式指定访问哪个父类的成员可以解决二义性的问题，但是数据冗余的问题还是无法解决

	a.Student::_name = "xxx";
	a.Teacher::_name = "yyy";
	
}
int main()
{
	Test();
	return 0;
}

#include <iostream>
#include <string>
using namespace std;

class Person{
public:
	string _name;
};
class Student : virtual public Person{
protected:
	int _stuId;
};
class Teacher : virtual public Person{
protected:
	int _teaId;
};
class Assistant : public Student, public Teacher{
protected:
	string _majorCourse;
};
void Test()
{

	Assistant a;
	a._name = "chenzhiao";
	
}
int main()
{
	Test();
	return 0;
}
// 在菱形继承的“肩膀处”添加完 virtual 关键字，完成虚拟继承，可以解决数据的二义性和冗余问题。我们来看一下监视窗口

#include <iostream>
#include <string>
using namespace std;

class A {
public:
	int _a;
};
// class B : public A
class B : public A {
public:
	int _b;
};
// class C : public A
class C : public A {
public:
	int _c;
};
class D : public B, public C {
public:
	int _d;
};

void Test()
{
	D d;
	cout << sizeof(d) << "字节" << endl;
	d.B::_a = 1;
	d.C::_a = 2;
	d._b = 3;
	d._c = 4;
	d._d = 5;
	
}
int main()
{
	Test();
	return 0;
}