Exit unending loop with Button

[Roelof]

Good day.

I have created a GUI that uses its buttons to change different states of a system. I want to be able to run a unending loop that reads data over the PCI bus inside of each event of a button. I have the buttons and I have the functions that run the unending loop that reads the PCI bus.
However, when the loop is running inside the event of the button I loose functionality of the gui.

So I basicly want to learn how to run a unending loop in the event of a button and still be able to control the GUI

I will try to explain with code:

void Controller::standby()
{	
               powerDownButton->setEnabled(true);
               standbyButton->setEnabled(false);
 
                int val = 1;
                while (val == 1)
                     {
                            read_data();
 
                         //here I nead something to exit the loop when a button is pressed;
                         //something that I can use to change val to another value and exit the loop
                        }

void Controller::standby()
{	
               powerDownButton->setEnabled(true);
               standbyButton->setEnabled(false);
              
                int val = 1;
                while (val == 1)
                     {
                            read_data();
                         
                         //here I nead something to exit the loop when a button is pressed;
                         //something that I can use to change val to another value and exit the loop
                        }

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Hope this post makes sense.
Thanks to anyone that can help!