returning reference from member function

[hobbycoder2013]

Hello, I am new registered user to this forum although i have browsed before. I already read one related thread from assassinbeast but that did not answer my question. So here is my question. Why doesn't dbl_b in my code on lines 19,20 below return 16 instead of 4? dbl_c works as expected. Thanks!

class data1
{
    int i;
public:
    data1() {i=1;}
    void seti(int ii) {i=ii;}
    void geti() {cout << i << endl;}

    void dbl_a(){i=i*2;}
    data1 dbl_b() {i=i*2;return *this;}
    data1& dbl_c() {i=i*2;return *this;}
};
int main()
{
    data1 d1,d2;
    d1.geti(); //outputs 1
    d1.dbl_a();
    d1.geti(); //outputs 2
    d1.dbl_b().dbl_b().dbl_b();
    d1.geti(); //outputs 4 not 16. Why is that?
    d1.dbl_c().dbl_c().dbl_c();
    d1.geti(); //outputs 32 as expected
}

[cire]

dbl_b() returns a copy of *this.

So, line 19 is equivalent to:

temp = d1.dbl_b() ;
temp2 = temp.dbl_b() ;
temp2.dbl_b() ;

You'll notice the method is only called once on d1, thus the output.

[hobbycoder2013]

That explains it perfectly. Thank you very much. So dbl_b gets called only once on d1.

The key is, as you said, dbl_b returns a copy of *this not the original *this (d1)

Based on what you said I modified the code a bit and now I get 16 on line 19.

class data1
{
    int i;
public:
    data1() {i=1;}
    void seti(int ii) {i=ii;}
    void geti() {cout << i << endl;}

    void dbl_a(){i=i*2;}
    data1 dbl_b() {i=i*2;return *this;}
    data1& dbl_c() {i=i*2;return *this;}
};
int main()
{
    data1 d1,d2;
    d1.geti(); //outputs 1
    d1.dbl_a();
    d1.geti(); //outputs 2
    (d1.dbl_b().dbl_b().dbl_b()).geti(); //now this shows 16
    d1.geti(); //outputs 4 since dbl_b is called only once on d1
    d1.dbl_c().dbl_c().dbl_c();
    d1.geti(); //outputs 32 as expected
}