I'm writing a CPP program, and I want to execute a function when the 'X'(shut down) button is pressed.
For example, I have an infinite loop that prints the same thing everytime it iterates, until the 'X' button is pressed, and I want to execute a function before the process ends.
Is there some kind of listener for this matter? Or some other solution maybe (like delaying the process shut down for a few seconds or something)?
Thanks!
If you want to execute something before your process ends, you can register an std::atexit handler. This function will be called before your process exits.
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I am programming a GUI with wxWidgets. I got a button to open a serial port and receive data. In there is a while(1) loop to constantly receive the data.
Now I want to do a "Disconnect" button to stop receiving.
Is there an event handler or a callback function to interrupt the while and jump out of the loop from the first button, when I press another button?
A wxButton sends a message when it is clicked. Create a handler for this message where you do your "interrruption".
Now, a loop can be only exited from its inner guts. I mean, inside the loop you should check a flag, and depending on the value of this flag continue or exit.
My advice is that you create a worker thread. When the button "connect" is clicked then you create the thread that receives data.
This thread checks an extern flag and finishes depending on the value of the flag.
The "disconnect" button click-handler just sets that extern flag to a value that makes the thread exits when it checks that flag.
Take a look at the thread sample provided with wxWidgets sources.
If you have a while(1) loop in the callback function for "button pressed", you will hang the UI. Callback functions must return quickly.
The quickest solution is to put the while(1) loop into a worker thread. That way your GUI won't hang.
The next problem is how to stop the loop. That's quite easy. Change the loop into:
while (keep_going.load()) {
....
where keep_going is of type std::atomic_bool. Then your "stop" button just calls keep_going.store(false).
I have a function that could run in an infinite loop, so I need a way of stopping the function at the press of a button. The problem is that while the function is running, the Qt widgets become unresponsive so I can't just set a stop bool when the button is pressed.
I am unsure of how to do this:
Connect the button signal to a QEventLoop and use that to stop the function (don't know how that would work) or have the function in a separate thread (never done that before)?
Basically exactly what the title says. I would like to update the text that a button contains every 1 second when the user presses that particular button. I have noted that when the program doesn't have focus it works alright and the text refreshes correctly but when I am hovering over the program or when I am trying to click on it's menu Windows inform me that the program is unresponsive and asks me if I want it terminated. When the loop finishes the program returns to its normal state. Also any action I might have done (like moving it around or closing it) while it was Sleep()-ing is executed after the loop. Here is a bit of code:
case ID_BUTTON_START:
// Code executed when pressing Start Button.
char startButtonText[30]; // Storing next loop text
for (int i=5; i>0; i--)
{
sprintf(startButtonText, "Starting in ... %d", i);
SendMessage(hwndButtonStart, WM_SETTEXT, 0, (LPARAM)(startButtonText));
Sleep(1000);
}
Is this normal? If not what's causing this?
The WndProc does not process messages asynchronously within an application which means all messages are expected to be handled quickly and a return value delivered immediately. You must not Sleep in the UI thread since it will block other UI events from being processed. Any heavy work or synchronous requests/jobs which are likely to take a long time should be performed in worker threads. There are at least three viable options:
Create a new (worker thread) for the task.
If the task is likely to be done often, use a thread pool instead.
Set and subscribe to timer events.
I think the call to Sleep() might be keeping you from returning from the WndProc, so your application is not processing the incomming events for 5 secs. I suggest you try to subscribe to 5 timer events in 1s, 2s,..., 5s. Like when the timer message is recieved the button text must change. I don't know a way how to do that off the top of my head.
Basically exactly what the title says. I would like to update the text that a button contains every 1 second when the user presses that particular button. I have noted that when the program doesn't have focus it works alright and the text refreshes correctly but when I am hovering over the program or when I am trying to click on it's menu Windows inform me that the program is unresponsive and asks me if I want it terminated. When the loop finishes the program returns to its normal state. Also any action I might have done (like moving it around or closing it) while it was Sleep()-ing is executed after the loop. Here is a bit of code:
case ID_BUTTON_START:
// Code executed when pressing Start Button.
char startButtonText[30]; // Storing next loop text
for (int i=5; i>0; i--)
{
sprintf(startButtonText, "Starting in ... %d", i);
SendMessage(hwndButtonStart, WM_SETTEXT, 0, (LPARAM)(startButtonText));
Sleep(1000);
}
Is this normal? If not what's causing this?
The WndProc does not process messages asynchronously within an application which means all messages are expected to be handled quickly and a return value delivered immediately. You must not Sleep in the UI thread since it will block other UI events from being processed. Any heavy work or synchronous requests/jobs which are likely to take a long time should be performed in worker threads. There are at least three viable options:
Create a new (worker thread) for the task.
If the task is likely to be done often, use a thread pool instead.
Set and subscribe to timer events.
I think the call to Sleep() might be keeping you from returning from the WndProc, so your application is not processing the incomming events for 5 secs. I suggest you try to subscribe to 5 timer events in 1s, 2s,..., 5s. Like when the timer message is recieved the button text must change. I don't know a way how to do that off the top of my head.
I am working with Qt, Directx 11 and C++. When my widget opens I start an Engine with system->Run(). This function calls every frame a function named Frame() as long as the variable done is set to false.
When the closing event is called in my Qt class, then I want to shutdown the engine. So I made a function named isDone() which sets the variable done to false and then I release all variables I have created with System->Shutdown(). But the problem is that the program crashes because when the closing event is called, the System->Run() function is interrupted as long as the closing event is over, but I want that the Run() function is executed after the call from the function isDone() before the System->Shutdown() function is executed.
Is there any possibility to make an interrupt in the closing event, so that other things in the queue are executed?
Is there any possibility to make an interrupt in the closing event, so that other things in >the queue are executed?
You can call qApp->processEvent in cycle, and wait some flag.