C++ std::queue push pop two different objects gets first object - c++

Question

I have following program:
int main(){
std::queue<Stone> Q;
Stone s1=Stone(8,8);
s1.setStoneColor(Color::WHITE);
Q.push(s1);
Stone curr = Q.back();
Q.pop();
Stone s2=Stone(7,7);
s2.setStoneColor(Color::BLACK);
Q.push(s2); //here Q contains x=8,y=8,colour=WHITE...why??
Stone curr2 = Q.back();
Q.pop();
return 0 ;
}
why is in the Queue at the end White stone with coords (x,y)=(8,8) ?
I thought that objects are copied into Queue by value, so there are not any references/pointers.
I also thought that somehow I didnt specified destructor?
Could it be somehow remedied by using smart pointers?
I come from java background so these weird errors are baffling...
Thanks.
I'm using Clion IDE if it helps.
EDIT: I tried the same thing in Xcode and after pushing second stone there was expected 7,7,black...
I believe it is Clion/Cmake/Debugger thing, anyone knowledgable about these?
Classes I'm using are:
enum Color{
BLACK=0,
WHITE=1,
BLANK=2
};
and class
class Stone {
int x = 0;
int y = 0;
bool discovered = false;
Color stoneColor;
public:
Stone(int _x, int _y) {
this->x = _x;
this->y = _y;
this->stoneColor = Color::BLANK;
}
void setDiscovered(bool value){
discovered=value;
}
bool getDiscovered(){
return discovered;
}
//setter
void setStoneColor(Color _stoneColor) {
stoneColor = _stoneColor;
}
//getter
Color getStoneColor()const {
return stoneColor;
}
int getPositionX() const {
return x;
}
int getPositionY() const{
return y;
}
bool operator==(const Stone &other) const {
if(this->x==other.getPositionX()&&this->x==other.getPositionY()&& this->stoneColor==other.getStoneColor()){
return true;
}
else{
return false;
}
}
};

Answer 1

When you do the first Q.pop(), will'd expect Q to be empty at-least before the next push(). Don't know how or why it had white stones. But concerning why you thought the object are copied by value or maybe you felt they were instead copied by reference, in this case they are copied by value and if not for the Q.pop you should expect them to be there cus they were declared in the local scope inside main function and they should persist at-least within this scope except destroyed.