[C++知识库]C++拷贝构造函数和赋值函数

在定义一个类时，会默认生成拷贝构造函数和赋值

拷贝构造函数

CObject(const CObject& oOBJ);

CObject::CObject(const CObject &oOBJ)
{
	//process data
}

什么时候用拷贝构造函数：

• 初始化对象
• 作为形参
• 作为返回值

赋值函数

CObject& operator=(const CObject& oOBJ);

CObject& CObject::operator=(const CObject &oOBJ)
{
	cout<<"This is operator = function."<<endl;
	if (this != &oOBJ)
	{
		cout << "process data assign." << endl;
	}
	return *this;
}

什么时候用赋值函数：

• 定义完成后的两个对象赋值时

示例

#include <iostream>
using namespace std;

class CObject
{
public:
	CObject();
	~CObject();
	CObject(const CObject& oOBJ);

	CObject& operator=(const CObject& oOBJ);
};

CObject::CObject()
{
	cout<<"This is construct function."<<endl;
}

CObject::~CObject()
{
	cout<<"This is destruct function."<<endl;
}
CObject::CObject(const CObject &oOBJ)
{
	cout<<"This is copy-construct function."<<endl;
}

CObject& CObject::operator=(const CObject &oOBJ)
{
	cout<<"This is operator = function."<<endl;
	if (this != &oOBJ)
	{
		cout << "process data assign." << endl;
	}
	return *this;
}

void test1(CObject oObj)
{

}

CObject test2(CObject oObj)
{
	return oObj;
}

int main(int argc, char* argv[])
{
	cout<<"**************use construct create oObjA**************************" << endl;
	CObject oObjA;
	cout << endl;

	cout << "**************use copy-construct create oObjB**************************" << endl;
	CObject oObjB = oObjA;
	cout << endl;

	cout << "**************use construct create oObjc**************************" << endl;
	CObject oObjC;
	cout << "**************copy data from oObjA to oObjc**************************" << endl;
	oObjC = oObjA;
	cout << endl;

	cout << "**************use copy-construct in parameter**************************" << endl;
	test1(oObjB);
	cout << endl;

	cout << "**************use copy-construct in return**************************" << endl;
	test2(oObjB);
	cout << endl;

	cout << "**************end **************************" << endl;
	return 0;
}

运行结果：