How to get rid of displaying the same QMessageBox twice in the following c++ code ?

[Ahti]

...
if (stopTime == 50){

        bufferTimer->stop();
        configMonitor() ;
        if (!GetMonitorBrightness(handle,&defaultMinBrightnessLevel,
                                  &defaultCurBrightnessLevel,
                                  &defaultMaxBrightnessLevel)){

            showErrorMessage->setWindowTitle("Error");  // showErrorMessage is a point to QMessageBox 
            showErrorMessage->setIcon(QMessageBox::Critical);
            showErrorMessage->setStandardButtons(QMessageBox::Ok);
            showErrorMessage->setText("Failed to get DDC/CI, please check if DDC/CI is Enabled.");
            showErrorMessage->exec();
            this->~EyeCare(); // EyeCare is the QMainWindow
}
...
void EyeCare::on_closeButton_clicked()
{ 
if (bufferTimer->isActive())
        stopTime = 50 ;
    if (!closeButtonClickedForTheFirstTime){

        closeButtonClickedForTheFirstTime = true ;

        if (startcaringButtonClickedForTheFirstTime)
            changeBrightness();
        else{
            if (GetMonitorBrightness(handle,&minBrightnessLevel,
                                     &curBrightnessLevel,&maxBrightnessLevel)){                
                showErrorMessage->setWindowTitle("Conform");
                showErrorMessage->setIcon(QMessageBox::Question);
                showErrorMessage->setText("Do you want to set brightness to default or leave it to Eye Care ? ");
                showErrorMessage->setStandardButtons(QMessageBox::Cancel);
                showErrorMessage->addButton(tr("Default"),QMessageBox::ActionRole);
                QPushButton *EyeCare = showErrorMessage->addButton(tr("EyeCare"),QMessageBox::ActionRole);
                showErrorMessage->setDefaultButton(EyeCare);
            }else{

                showErrorMessage->setWindowTitle("Error");
                showErrorMessage->setIcon(QMessageBox::Critical);
                showErrorMessage->exec();
                closeAnimation();
                this->close() ;
            }
        }
...
}
...

I show error message when ' GetMonitorBrightness()' windows api functions fails by returning false.

so I get the same error message twice why ? shouldn't my app close when it encounters this line:
" this->~EyeCare() ; "
is it because they both run as a separate thread ? if yes then how can i terminate the second thread ( on_closeButton_clicked() ) in the first thread so that i can get that error message only once ?

[kshegunov]

@Ahti
Please read how C++ manages objects' lifetimes.

For the FAQ:
https://isocpp.org/wiki/faq/dtors#dont-call-dtor-on-obj-allocd-via-new