Qt QEventLoop Error: 'Cannot be used without QApplication' - Solution and Explanation

The QEventLoop is a class in the Qt framework used for processing events in a non-blocking manner. It's commonly employed in GUI applications to maintain responsiveness while waiting for user input or other events.

However, the QEventLoop requires a QApplication instance to be created before it can be used. This is because QApplication initializes the Qt event loop and provides the main event loop for the application.

If you encounter the error message 'QEventLoop: Cannot be used without QApplication', it indicates that you're attempting to use QEventLoop without first initializing QApplication.

To resolve this error, ensure you create an instance of QApplication before utilizing QEventLoop. Here's an example of how to create a QApplication instance:

#include <QApplication>  
  
int main(int argc, char *argv[]) {  
    QApplication app(argc, argv);  
  
    // Your code here  
  
    return app.exec();  
}  

By creating a QApplication instance at the beginning of your code, you can then employ QEventLoop to process events non-blockingly.