C++ Object variables in list don't update during iteration

Question

When iterating through a list, the variables of the object in the list won't update, with debugging it looked like the variables only updated temporarily until the loop ended. Why is this? I've been looking for a very long time.

for (std::list<GUI>::iterator it = allguis.begin(); it != allguis.end(); ++it) {
    GUI gui = *it;
    speed = 5
   if (gui.activated) {
    gui.position.x = gui.position.x + gui.distanceX * speed;
    gui.position.y = gui.position.y + gui.distanceY * speed;
           }
   }                

And the GUI class:

class GUI
{
public:
    sf::Vector2f position = sf::Vector2f(0,0);
    int sizex;
    int sizey;
    bool activated;
    float rotation;
    int damage;
    float distanceX;
    float distanceY;

};

Answer 1

GUI gui = *it; creates a local variable initialized with a copy of the value stored in container. You should use a refence instead:

GUI & gui = *it;

Or you can use C++11-style loop:

speed = 5; // no point in updating it on every iteration
for(auto & gui: allguis)
{
    if(gui.activated)
    {
        gui.position.x = gui.position.x + gui.distanceX * speed;
        gui.position.y = gui.position.y + gui.distanceY * speed;
    }
}