C++ 拷贝构造函数与赋值的区别

#include<iostream>
using namespace std;
class date
{
public:
	date(int year=0, int month=0, int day=0)
	{
		_year = year;
		_month = month;
		_day = day;
	}
	date(const date& d)//拷贝构造函数
	{
		this->_year = d._year;
		this->_month = d._month;
		this->_day = d._day;
	}
	void print()
	{
		cout << _year << "-" << _month << "-" << _day << endl;
	}
private:
	int _year;
	int _month;
	int _day;
};

int main()
{
	date d1(20244, 4, 24);
	date d2=d1;
	date d3;
	d3= d1;//编译器会自动将其转化为d3(d1);
	return 0;
}

#include<iostream>
using namespace std;
class date
{
public:
	date(int a=1,int b=1)
	{
		_a = a;
		_b = b;
	}
	date(const date& d)
	{
		_a = d._a;//成员变量简单的赋值
		_b = d._b;
	}
	void print()
	{
		cout << _a << ',' << _b << endl;
	}
	~date()
	{
		cout << "~date" << endl;
	}
private:
	int _a;
	int _b;
};


int main()
{
	date d1(2,5);
	date d2(d1);
	d2.print();
	return 0;
}

#include<iostream>
using namespace std;
class date
{
public:
	date(int b=1)
	{
		_a =new int[4];
		_b = b;
	}
	date(const date& d)
	{
		_a = d._a;
		_b = d._b;
	}
	void print()
	{
		cout << _a << ',' << _b << endl;
	}
	~date()
	{
		free(_a);//拷贝后两个成员变量都指向同一块空间,会造成多次析构
		cout << "~date" << endl;
	}
private:
	int* _a;
	int _b;
};


int main()
{
	date d1(5);
	date d2(d1);
	d2.print();
	return 0;
}

#include<iostream>
using namespace std;
class date
{
public:
	date(int b=1)
	{
		_a =new int[4];
		_a[0] = 10;
		_b = b;
	}
	date(const date& d)
	{
		_a = new int[4];
		memcpy(_a, d._a, sizeof(int) * 4);//将d2的数据拷贝过来
		_b = d._b;
	}
	void print()
	{
		cout << _a[0] << ',' << _b << endl;
	}
	~date()
	{
		free(_a);
		cout << "~date" << endl;
	}
private:
	int* _a;
	int _b;
};


int main()
{
	date d1(5);
	date d2(d1);
	d2.print();
	return 0;
}