copy constructor

Objects of the same class have complete structure in memory , If copying or copying as a whole is completely feasible . This copy process only needs to copy data members , And function members are shared （ There is only one copy ）. When creating an object, another object of the same class can be used to initialize the storage space of the object , The constructor used in this case is called copy constructor .

When initializing one object with another , Will call the copy constructor .

If there is no copy constructor , The system will give a default copy constructor .

The following program creates several objects ：（ A total of 5 Objects ）

#include<iostream>
using namespace std;

class Object
{
private:
	int value;
public:
	Object() { cout << "Object::Object " << this << endl; }// Default constructor 
	Object(int x) :value(x) { cout<<"Object::Object:  " << this << endl; }// Constructor with parameters 
	~Object() { cout << "Object::~Object  " << this << endl; }// Destructor 
	void SetValue(int x) { value = x; }
	int Getvalue() const{ return value; }
	Object(const Object &obj):value(obj.value)
	{
		cout << "Copy Creat" << endl;
	}// copy constructor 
	
};
Object fun(Object obj)//3.objx  initialization obj, Create an object 
{
	int val = obj.Getvalue();
	Object obja(val);//4. Building an object 
	return obja;// When function returns , Give a copy to a temporary quantity （ Dead value ）,5. Build a dead value object 
}
int main()
{
	Object objx(0);//1. Create an object , Constructors 
	Object objy(0);//2. Create an object constructor 
	objy = fun(objx);// call fun() function 

	return 0;
}

Construct the dead value in the stack frame of the main function , If the function is built in the stack , function return After the end , There will be no dead value . 

If you want to create fewer objects ,

1.2. Using a reference

Object fun(Object &obj)// If you don't want the reference to change the original object , Add const ,Object fun(const Object &obj)
{
	int val = obj.Getvalue();
	Object obja(val);
	return obja;
}

 2. Reference return

Reference return , Build dead values into functions .