技術標籤：程式語言c++

從現有物件建立新物件時，是Copy Constructor。 當已初始化的物件從另一個現有物件中分配了新值時，是Assignment Operator。當然,看到這句話,你還是不懂.下面看一下程式碼

#include<iostream> 
#include<stdio.h> 

using namespace std; 

class Test 
{ 
	public: 
	Test() {} 
	Test(const Test &t) 
	{ 
		cout<<"Copy constructor called "<<endl; 
	} 
	
	Test& operator = (const Test &t) 
	{ 
		cout<<"Assignment operator called "<<endl; 
		return *this; 
	} 
}; 

// Driver code 
int main() 
{ 
	Test t1, t2; 
	t2 = t1; //這裡是Assignmeng operator
	Test t3 = t1; //這裡是copy constrctor
	getchar(); 
	return 0; 
} 
 

看到程式碼是不是清楚了些,不過你記得小時候這樣的程式碼

#include<iostream> 
#include<stdio.h> 

using namespace std;

class Test
{
public:
	Test() {}
	int a = 0;
	
};

// Driver code 
int main()
{
	Test t1, t2;
	t1.a = 3;
	t2 = t1;
	cout << t2.a << endl;  //輸出3
	Test t3 = t1;
	cout << t3.a << endl; //輸出3
	getchar();
	return 0;
}
 

你沒有寫copy construct 怎麼也會賦值上,這是因為編譯器偷偷的給你把copy construct和assignment operator寫上去了. 可以這樣搞一下

#include<iostream> 
#include<stdio.h> 

using namespace std;

class Test
{
public:
	Test() {}
	int a = 0;
	Test(const Test &t) = delete;
	

	Test& operator = (const Test &t) = delete;
	
};

// Driver code 
int main()
{
	Test t1, t2;
	t1.a = 3;
	t2 = t1;  //編譯錯誤
	cout << t2.a << endl;
	Test t3 = t1; //編譯錯誤
	cout << t3.a << endl;
	getchar();
	return 0;
}
 

這樣,就相當於你警告編譯器不要多事.