一起来学习C++的构造和析构

#include <iostream>
using namespace std;
class MM 
{
public:
	//MM() = delete;     删掉默认的构造函数
	MM(string mmName, int mmAge) 
	{
		name = mmName;
		age = mmAge;
		cout << "带参构造函数" << endl;
	}
	//MM() 
	//{
	//	cout << "无参构造函数" << endl;
	//}
	MM() = default;  //使用的是默认无参构造函数
	void print() 
	{
		cout << name << " " << age << endl;
	}
protected:
	string name="Lisa";
	int age=18;
};
//为了能够构造不同长相的对象，我们会给构造函数缺省处理
class Boy
{
public:
	//Boy(string mname="", int mage=19) 
	//{
	//	name = mname;
	//	age = mage;
	//}
	//上面函数 等效可以实现下面三个函数的功能
	Boy() {}
	Boy(string mName) { name = mName; }
	//出错：没有与之匹配的构造函数
	Boy(string mName, int mage) { name = mName; age = mage; }
protected:
	string name;
	int age;
};
//初始化参数列表的写法
string girlName = "Baby";
class  Student 
{
public:
	Student(string mname="", int mage=18) :name(mname), age(mage) 
	{
		cout << "初始化参数列表" << endl;
		//继承和类的组合必须采用初始化参数列表写法
	}
	Student(int mage) :name(girlName), age(mage) {}
protected:
	string name;
	int age;
};
//构造函数可以调用另一个构造函数初始化数据
class TT 
{
public:
	TT(string name, int age) :name(name), age(age) {}
	//委托构造：允许构造函数调用另一个构造函数
	TT():TT("默认",18) {}     //没有给数据初始化
	void print() 
	{
		cout << name << "\t" << age << endl;
	}
protected:
	string name;
	int age;
};
int main() 
{
	//MM mm;     构造无参的对象，需要无参构造函数
	MM mm("mm", 28);
	mm.print();
	MM girl;
	girl.print();
	Boy boy1;
	Boy boy2("流浪之子");
	Boy boy3("王子", 18);
	TT  tt;
	tt.print();
	return 0;
}

#include <iostream>
#include <string>
using namespace std;
class MM 
{
public:
	MM() = default;
	MM(string name, int age) :name(name), age(age) {}
	void print() 
	{
		cout << name << "\t" << age << endl;
	}
	//拷贝构造
	MM(const MM& mm)			 //MM girl(mm);
	{
		name = mm.name;  //girl.name=mm.name
		age = mm.age;	 //girl.age=mm.age
		cout << "拷贝构造" << endl;
	}

protected:
	string name;
	int age;
};
void printData(MM mm)   //MM mm=实参;
{ 
	mm.print();
}
void printData2(MM& mm) //不存在拷贝本
{
	mm.print();
}
int main() 
{
	MM mm("mm", 18);
	mm.print();
	//显示调用调用
	cout << "显示调用调用" << endl;
	MM girl(mm);        //通过一个对象创建另一个对象
	girl.print();
	//隐式调用
	cout << "隐式调用" << endl;
	MM girl2 = mm;		//拷贝构造
	girl2.print();
	MM girl3;
	girl3 = mm;			//运算符重载
	girl3.print();		
	//函数传参
	cout << "第一种调用形态" << endl;
	printData(mm);
	cout << "第二种调用形态" << endl;
	printData2(mm);
	//无名对象 匿名对象
	MM temp;
	temp = MM("匿名", 18);
	temp.print();
	//匿名对象创建对象时候，拷贝构造一定要用const修饰
	MM temp2 = MM("匿名", 199);
	return 0;
}

#include<iostream>
#include <cstring>
#include <string>
using namespace std;
class MM 
{
public:
	MM(const char* mname, int age) :age(age)
	{
		name = new char[strlen(mname) + 1];
		strcpy_s(name, strlen(mname) + 1, mname);
	}
	void print() 
	{
		cout << name << "\t" << age << endl;
	}
	MM(const MM& object) 
	{
		//name = object.name;
		name = new char[strlen(object.name) + 1];
		strcpy_s(name, strlen(object.name) + 1, object.name);
		//name = object.name;
		age = object.age;
	}
	~MM() 
	{
		delete[] name;
	}
protected:
	char* name;
	int age;
};
int main() 
{
	{
		MM mm("baby", 19);
		MM girl(mm);
		MM gm = mm;
		mm.print();
		girl.print();
		gm.print();
	}
	return 0;
}

#include <iostream>
#include <string>
using namespace std;
class MM 
{
public:
	MM(string name="x") :name(name) {
		cout << name;
	}
	~MM(){
		cout << name;
	}
protected:
	string name;
};
int main() 
{
	{
		MM mm1("A");			//A
		static MM mm2("B");		//B   程序关闭时候才死亡，最后析构
		MM* p3 = new MM("C");	//C
		MM mm4[4];				//xxxx
		delete p3;				//C  delete 直接调用析构
		p3 = nullptr;
								//xxxxAB
	}
	//ABCxxxxCxxxxAB
	return 0;
}

#include <iostream>
#include <string>
using namespace std;
struct MM 
{
	//默认为公有属性
	//类中默认属性是私有属性
//protected:
	string name;
	int age;
public:
	MM(string name) :name(name) 
	{
		cout << "构造函数" << endl;
	}
	MM(const MM& object) 
	{
		name = object.name;
		age = object.age;	
		cout << "拷贝构造" << endl;
	}
	~MM() 
	{
	}
};
int main() 
{
	//采用创建时候赋值的方式，也是调用构造函数
	//MM object = { "lisa",19 };  错误，因为没有两个参数的构造函数
	MM  object = { "lisa" };
	cout << object.name << "\t" << object.age << endl;
	//C++结构体一旦写了构造函数，就必须按照C++类的方式的去用
	MM mm(object);
	cout << mm.name << "\t" << mm.age << endl;
	return 0;
}

class Boy
{
public:
	Boy() {}
	void print() 
	{
		cout << a << "\t" << b << "\t" << c << endl;
	}
protected:
	int a;
	int b;
	int c;
};
int main()
{
    return 0;
}