Stop qt application in infinite loop when main window is closed - c++

Question

My main application class is USB_Packet_Analyzer which processes some files, but also supports reading from a file to which somebody still writes. In that case, I have an infinity loop which checks whether something new was written in this file and if so, I continue in processing. In every iteration of loop I am calling QCoreApplication::processEvents();.
The problem is that when I close main window of app, it wont stop the application. If I check QApplication::topLevelWidgets().size() it is still 1, and QApplication::topLevelWidgets().at(0)->isVisible() is false. Why isn't it closing my window? Can I connect some signal to detect whether red cross on window was clicked or not? I know that when getting into this kind of loops i might use QThread, but I'd rather not get this involved. Is there any solution for my problem?

Answer 1

Take a look at the QFileSystemWatcher Class and its fileChanged signal.
#include <QFileSystemWatcher>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
private:
QFileSystemWatcher* fileWatcher;
Ui::MainWindow*ui;
};
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent)
{
createUi();
fileWatcher = new QFileSystemWatcher(this);
connect(fileWatcher, SIGNAL(fileChanged(QString)), this, SLOT(fileChangedSlot(QString)));
QFileInfo file("file_to_watch.txt");
if (file.exists())
{
fileWatcher->addPath(file.absoluteFilePath());
}
}
void MainWindow::fileChangedSlot(const QString &path)
{
if (fileWatcher->files().contains(path))
{
qDebug() << "File changed" << path;
}
}

Answer 2

You can using of system interrupt signal to manage a Boolean to breaking your infinite loop or exiting the application.
e.g:
#include <iostream>
#include <csignal>
using namespace std;
void InterruptSignalHandler(int signal_number) {
cout<< "Signal Number is "<<signal_number<<endl;
exit(signal_number);
}
int main()
{
signal(SIGINT, InterruptSignalHandler);
string a;
while(true)
{
cout<<">";
cin >> a;
}
return 0;
}