Move constructor problem

[Lio]

If I dont include the move constructor(line 30) ,if I do include it --reference to local var temp returned(enabled by default

#include <iostream>
using namespace std;
class MyObj
{
public:
    MyObj()
        :varI(0),varD(0)
    {
    }

    MyObj(int MyObj,double b)
        :varI(MyObj),varD(b)
    {
    }
    void print()
    {
        cout<<"int:"<<varI<<" double:"<<varD<<endl;
    }
    MyObj& operator+(MyObj &o)
    {
        MyObj temp;
        temp.varI=varI;
        temp.varD=varD;
        temp.varI+=o.varI;
        temp.varD+=o.varD;
        return temp;
    }
    int getVarI()  {return varI;}
    int getVarD()  {return varD;}
    MyObj (MyObj && o)//MOve constructor
    {
        varI=o.varI;
        varD=o.varD;
    }
private:
    int varI;
    double varD;
};
ostream& operator<<(ostream& out,MyObj & o)
{
    out<<o.getVarI()<<" "
    <<o.getVarD()<<endl;
    return out;
}
int main()
{
    MyObj o1(3,33.33);
    MyObj o2(2,22.22);
    MyObj o3=o1+o2;    //reference to local var temp returned(enabled by default
    o3.print();
    MyObj o4;
    cout<<o4;
    MyObj  o5(move(o1));
}

[Peter87]

When you declare a move constructor the implicitly defined copy constructor will be deleted.
There is no reason why you should define a move constructor for MyObj because it will do the same as the copy constructor anyway.

[Lio]

Thanks,I am learning C++ now ,and it was explained that if our object is big is better to use move instead of copy.
Can you explaine why implicitly defined copy constructor will be deleted

[Peter87]

Lio wrote:

Can you explaine why implicitly defined copy constructor will be deleted

Because the standard says so

_{C++11 §12.8/7}

If the class definition declares a move constructor or move assignment operator, the implicitly declared copy constructor is defined as deleted;

If there is a reason do define a move constructor the default copy constructor will almost certainly don't work. I guess that is the reason for this rule.

[Lio]

Thanks
I though,that I dont have copy constructor declare,could you point where is the copy constructor

[guestgulkan]

You should get that reference to local var temp returned(enabled by default whether or not
you have the move contructor - because the operator+ function does return a reference to a local variable...

Lio wrote:

Thanks,I am learning C++ now ,and it was explained that if our object is big is better to use move instead of copy.

Who said that - or what book did you read that from??
That is totally incorrect!