Quit, Exit qApp (program) if error?

[Arsenic]

I am trying to figure out how to properly exit and destroy all my classes if say an error happens.

Trying to make like a close the application if this message box pops up.

Doing this:

qApp->exec();
		return;

qApp->exec();
		return;

To copy to clipboard, switch view to plain text mode 

Works, but it leaves the Process in Task Manager alive just the window doesn't show up.

[JimDaniel]

exec() starts the event loop, its called in main normally.

You probably want qApp->quit();

[Arsenic]

If I use quit(), the error message comes up and then the program starts up anyway. It is suppose to quit the whole program and destroy everything.

I mean how do people put like a File > Exit ?? What do they connect() to "exit"?

[JimDaniel]

Your situation sounds to me like a situation I've had before, where you need to do a test in the main window/widget constructor, and if it fails you need to exit the program, but as this is being called before app.exec() in main(), it doesn't work properly. My solution was a hack, but it should work.

QTimer::singleShot(250, qApp, SLOT(quit()));

QTimer::singleShot(250, qApp, SLOT(quit()));

To copy to clipboard, switch view to plain text mode 

Probably someone here with more experience should step in and suggest a more correct solution. I would like to know myself.

[Arsenic]

Thanks, it seems to work. I think my main problem was I was trying to use it in my class (QMainWindow):

I tried
qApp->quit();

that didn't do anything.

I tried
close(); (because QMainWindow has a close function)
but apparently, your singleShot timer works awesome, thanks I had forgotten about that.

[aamer4yu]

Just a thought -...
Wont it be better if we use some kind of factory for the objects ??
The factory may return a valid object if the parameters meet the condition, or else it returns null.

[JimDaniel]

Its been bothering me I suggested so clearly a hackish method of solving the problem. I realized today a better solution. Not sure why it didn't occur to me before:

int main(int argc, char * argv[])
{
     QApplication app(argc, argv);
     QWidget myWidget;
 
     bool passed_test = myWidget.testForSomething();
     if(passed_test)
     {
         myWidget.show();
         return app.exec();
     }
     else
     {
         return 1;
     }
}

int main(int argc, char * argv[])
{
     QApplication app(argc, argv);
     QWidget myWidget;
     
     bool passed_test = myWidget.testForSomething();
     if(passed_test)
     {
         myWidget.show();
         return app.exec();
     }
     else
     {
         return 1;
     }
}

To copy to clipboard, switch view to plain text mode 

[jpn]

Calling QApplication::quit() indeed doesn't have any effect if one later calls QApplication::exec().

[MarkoSan]

Well, I have following chunk of code:

{
    // sets up database paramaters
    m_Database=QSqlDatabase::addDatabase(db_type);
    m_Database.setHostName(db_host);
    m_Database.setUserName(db_username);
    m_Database.setPassword(db_password);
    m_Database.setDatabaseName(db_name);
    // tries to connect to database
    m_bConnectionEstablished=m_Database.open();
    if(!m_bConnectionEstablished)
    {
        //qFatal("Failed to connect to database. Aborting.");
/*
        int ret=QMessageBox::critical(0,
                                      tr("Critical Error"),
                                      tr("Failed to connect to database. Aborting."));
*/
        QString errorString(m_Database.lastError().databaseText());
 
        errorString.append(": ");
        errorString.append(m_Database.lastError().driverText());
        int ret=QMessageBox::critical(0,
                                      tr("Critical Error"),
                                      errorString);
 
        qApp->quit();    // terminates application, does not work?!
    }

{
    // sets up database paramaters
    m_Database=QSqlDatabase::addDatabase(db_type);
    m_Database.setHostName(db_host);
    m_Database.setUserName(db_username);
    m_Database.setPassword(db_password);
    m_Database.setDatabaseName(db_name);
    // tries to connect to database
    m_bConnectionEstablished=m_Database.open();
    if(!m_bConnectionEstablished)
    {
        //qFatal("Failed to connect to database. Aborting.");
/*
        int ret=QMessageBox::critical(0,
                                      tr("Critical Error"),
                                      tr("Failed to connect to database. Aborting."));
*/
        QString errorString(m_Database.lastError().databaseText());

        errorString.append(": ");
        errorString.append(m_Database.lastError().driverText());
        int ret=QMessageBox::critical(0,
                                      tr("Critical Error"),
                                      errorString);

        qApp->quit();    // terminates application, does not work?!
    }

To copy to clipboard, switch view to plain text mode 

What I want to achieve, if database connection fails, application must terminate immediately. qApp->quit() does not work, are there any other ideas?

[jpn]

When does this chunk of code get executed? Before entering to the event loop (ie. before calling QCoreApplication::exec())?

[MarkoSan]

Here is code:

eROSystem w; 
    w.showMaximized();
    pIntroWindow->finish(&w);    // sets splash window closing time
    delete pIntroWindow;    // deletes pIntroWindow
    a.connect(&a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()));
    return a.exec();

eROSystem w; 
    w.showMaximized();
    pIntroWindow->finish(&w);    // sets splash window closing time
    delete pIntroWindow;    // deletes pIntroWindow
    a.connect(&a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()));
    return a.exec();

To copy to clipboard, switch view to plain text mode 

Database code is executed in following line:

eROSystem w;

eROSystem w;

To copy to clipboard, switch view to plain text mode 

. This is the first line of this code chunk.

[jpn]

So, first in the eROSystem constructor you call QCoreApplication::quit() and then later in main() you call QCoreApplication::exec(). That won't make the application quit. First you tell it to exit the event loop, then you tell it to enter the event loop.