c++ pointers return 0 value - c++

Question

Im pretty new to C++ and I have problem with pointers. Can someone please explain me how does this code return 0 for y, instead of 20?
#include <iostream>
using namespace std;
class Test
{
private:
int x;
int y;
public:
Test (int x = 0, int y = 0) { this->x = x; this->y = y; }
Test setX(int a) { x = a; cout << "hello"; return *this; }
Test setY(int b) { y = b; cout << "world"; return *this; }
void print() { cout << "x = " << x << " y = " << y << endl; }
};
int main()
{
Test obj1;
obj1.setX(10).setY(20);
obj1.print();
return 0;
}
}

Answer 1

Your methods are returning copies of the test object.
Test setX(int a) { x = a; cout << "hello"; return *this; }
Test setY(int b) { y = b; cout << "world"; return *this; }
So obj1.setX(10) applies to the original, but then .SetY(20) applies to the copy.
You need to return by reference:
Test& setX(int a) { x = a; cout << "hello"; return *this; }
Test& setY(int b) { y = b; cout << "world"; return *this; }

Answer 2

You are trying to implement a design called "function chaining". To do this, you must return a reference to the current object, not a brand new object:
Test& setX(int a) { x = a; cout << "hello"; return *this; }
Test& setY(int b) { y = b; cout << "world"; return *this; }
Since you are returning the current object, this will now work. Your example was returning a brand new Test object, which is why you were seeing 0 as the output.

Answer 3

If you want to chain calls to Test, your setters need to return a reference on Test instance.
If you do not return a reference to the object, it is not udpated, a copy of it is updated.
Without the reference what you wrote is equivalent to:
Test tmp = obj1.setX(10);
tmp.setY(20)
obj1.print()
(tmp is a "local" variable created by the compiler)
Fixed code below:
#include <iostream>
using namespace std;
class Test
{
private:
int x;
int y;
public:
Test (int x = 0, int y = 0) { this->x = x; this->y = y; }
Test &setX(int a) { x = a; cout << "hello"; return *this; }
Test &setY(int b) { y = b; cout << "world"; return *this; }
void print() { cout << "x = " << x << " y = " << y << endl; }
};
int main()
{
Test obj1;
obj1.setX(10).setY(20);
obj1.print();
return 0;
}