day07_类的声明

声明和实现分离

#pragma once

// 声明 .h 头文件
class Person {
	int m_age;
public:
	Person();
	~Person();
	void setAge(int age);
	int getAge();
};


#include "Person.h"
#include <iostream>
using namespace std;

// ::是域运算符
// 实现 .cpp 源文件
Person::Person() {
	cout << "Person()" << endl;
}

Person::~Person() {
	cout << "~Person()" << endl;
}

void Person::setAge(int age) {
	this->m_age = age;
}

int Person::getAge() {
	return this->m_age;
}

命名空间

命名空间可以用来避免命名冲突

命名空间不影响内存布局

#include <iostream>
#include "Car.h"
#include "Person.h"
//using namespace KP;
using namespace std;

void test() {
	cout << "test()" << endl;
}

namespace FX {
	int g_no;

	class Person {
	public:
		int m_age;
	};

	void test() {
		cout << "FX::test()" << endl;
	}
}
//
namespace KP {
	int g_no;

	class Person {
	public:
		int m_height;
	};

	void test() {
		cout << "KP::test()" << endl;
	}
}

void test1() {
	FX::g_no = 1;
	KP::g_no = 2;

	FX::Person *p1 = new FX::Person();
	p1->m_age = 10;

	KP::Person *p2 = new MJ::Person();
	p2->m_height = 180;

	test();
	FX::test();
	KP::test();
}

namespace KP {
	int g_no;

	class Person {
	public:
		int m_height;
	};

	void test() {
		cout << "MJ::test()" << endl;
	}
}

void test2() {
	/*using namespace MJ;
	g_no = 10;
	Person person;
	test();*/

	/*using MJ::g_no;
	using MJ::Person;
	g_no = 10;
	Person person;*/
}

namespace KP {
	namespace SS {
		int g_no;
		class Person {

		};

		void test() {

		}
	}

	void test() {

	}
}

void test() {

}

void test3() {
	test();
	// 默认的命名空间，没有名字
	::test();

	::KP::SS::g_no = 30;

	KP::SS::g_no = 20;

	using namespace KP;
	SS::g_no = 30;

	using namespace KP::SS;
	g_no = 10;
}

int main() {
	KP::Car car;
	KP::Person person;

	getchar();
	return 0;
}

继承

父类的成员变量在前，子类的成员变量在后

//struct Person {
//	int m_age;
//	void run() {
//		cout << "run()" << endl;
//	}
//};
//
//struct Student : Person {
//	int m_score;
//	void study() {
//		cout << "study()" << endl;
//	}
//};
//
//struct Worker : Person {
//	int m_salary;
//	void work() {
//		cout << "work()" << endl;
//	}
//};

void test() {
	/*Student student;
	student.m_age = 18;
	student.m_score = 100;
	student.run();
	student.study();*/
}

struct Person {
	int m_age;
};

struct Student : Person {
	int m_no;
};

struct GoodStudent : Student {
	int m_money;
};

int main() {
	// 12
	GoodStudent gs;
	gs.m_age = 20;
	gs.m_no = 1;
	gs.m_money = 2000;

	cout << &gs << endl;
	cout << &gs.m_age << endl;
	cout << &gs.m_no << endl;
	cout << &gs.m_money << endl;

	// 4
	Person person;

	// 8
	Student stu;

	cout << sizeof(Person) << endl;
	cout << sizeof(Student) << endl;
	cout << sizeof(GoodStudent) << endl;

	getchar();
	return 0;
}

成员访问权限

• 成员访问权限、继承方式有3种
  • public:公共的，任何地方都可以访问(struct默认)
  • protected:子类内部、当前类内部可以访问
  • prvate:私有的，只有当前类内部可以访问(class默认)
• 子类内部访问父类成员的权限，是以下2项中权限最小的那个
  • 成员本身的访问权限
  • 上一级父类的继承方式
• 开发中用的最多的继承方式是public，这样能保留父类原来的成员访问权限
• 访问权限不影响对象的内存布局

class Person {
public:
	int m_age;
	void run() {

	}
};

class Student : public Person {
	int m_no;
	void study() {
		m_age = 10;
	}
};

class GoodStudent : public Student {
	int m_money;
	void work() {
		m_age = 10;
	}
};

class Person {
private:
	int m_age;
public:
	int m_no;
};

int main() {
	Person person;
	person.m_no = 20;

	getchar();
	return 0;
}