How to get rid of segmentation fault in the following code ?

Ahti

When I call 'on_smartModeExitButton_triggered()' function first time ( that is in the if statement of 'on_startcaringButton_clicked' function through 'showSmartModeEnabled()' function) it runs perfectly fine but when I try to call it again from the else part I get segmentation fault. why ?

My Header File:

QMessageBox *smartMode ;
QTimer *notClosed ;

My Code:

void EyeCare::on_smartModeExitButton_triggered(){

   smartMode->hide() ;
   notClosed->stop() ;
}

void EyeCare::messageDisplayTime(){

    notClosed = new QTimer(this) ;
    connect(notClosed,SIGNAL(timeout()),this,SLOT(on_smartModeExitButton_triggered(smartMode))) ;
    notClosed->start(2000) ;
}

void EyeCare::showSmartModeEnabled(){

    smartMode = new QMessageBox(this) ;
    smartMode->setWindowFlags(Qt::FramelessWindowHint);
    smartMode->setMaximumSize(100,100);
    smartMode->setMinimumSize(100,100);
    smartMode->setText("Smart Mode Enabled");
    smartMode->setStyleSheet("font: 75 bold 12pt Arial; background-color:#D2D2D2;");
    smartMode->setGeometry(370,300,100,100);
    smartMode->setStandardButtons(QMessageBox::NoButton);
    smartMode->show();
    messageDisplayTime() ;
}

void EyeCare::on_startcaringButton_clicked()
{

    if (startcaringButtonClickedFlag){

         startcaringButtonClickedFlag = 0 ;          
         showSmartModeEnabled() ;
}else{

        QString style = smartMode->text() ;
        style.replace(11,7,"Disabled") ;
        smartMode->setText(style);
        smartMode->show();
        messageDisplayTime() ; // here in this function i  get segmentation fault at the first line of code ( that is at 'smartMode->hide()' )
    }
}

how can i fix it ?

VRonin

connect(notClosed,SIGNAL(timeout()),this,SLOT(on_smartModeExitButton_triggered(smartMode))) ; this won't work, it should be connect(notClosed,SIGNAL(timeout()),this,SLOT(on_smartModeExitButton_triggered())) ;

SGaist

Hi,

To add to @VRonin, you're not doing any checks for smareMode's validity. It will only be valid once you called showSmartModeEnabled. So you are likely accessing a dangling pointer.

You are also leaking memory since each time you call showSmartModeEnabled it will create a new QMessageBox and the same for messageDisplayTime and QTimer.

Ahti

@VRonin
i know that was a mistake i removed that argument
and it still doesn't work i am getting segmentation fault

Ahti

@SGaist

okay by adding these two lines will i be able to get rid of memory leak ?

in the ' on_smartModeExitButton_triggered() ' function i added this at end:

notClosed = NULL ;

and in the else part ( in 'on_startcaringButton_clicked()' function ) i added this in the end:

smartMode = NULL ;

would adding those two lines stop memory leak ?? and how could i show the same messagebox in the else part without creating another one ( if you say its a dangling pointer how could i fix it ) ?

Ahti

@SGaist

i did this:

void EyeCare::on_smartModeExitButton_triggered(int value){

   if (value){
       if (test != smartMode)
           smartMode = test ;
       smartMode->setVisible(false); ;
   }else
       smartMode->setVisible(false); ;

   notClosed->stop() ;
   notClosed = NULL ;
}

the value is set to zero if you call it from if part otherwise its one and i created another variable of type QMessageBox namely test that stores the address of smartMode before calling messageDisplayTime() function in the else part ( because in else part it does successfully show the messagebox with smartMode pointer which means its not corrupted until then ) okay now after all this set i don't get any segmentation problem but the smartMode->hide() doesn't work now it doesn't hide the messagebox after every 2 seconds why ?

This is in the else part:

...
test = smartMode ;  // test is declared as QMessageBox 
messageDisplayTime(1) ;
...

And this is in the if part:

...
 messageDisplayTime(0) ;
...

Ahti

@SGaist

I fixed the problem and here is my new code :

...
}else{
       QString style = smartMode->text() ;
        style.replace(11,7,"Disabled") ;
        smartMode->setText(style);
        smartMode->show();
// I replaced messageDisplayTime() function with this
        notClosed->start(1500);  
}

I fixed the problem but there will still be memory leak right ?
because when user again clicks on the startcaringButton my code will create a new messagebox ( in if part ) and will also create a new timer ??????
i tried to destroy and delete the messagebox in the else part after 'notClosed' timer but i can't as the parent of messagebox is my app itself. So how can i just delete it ? in the else part ? i know i can set no parent to messagebox but that will add extra code right ? so i there any way that i can get rid of memory leak ?

SGaist

You can build both the timer and dialog only once and re-use them for example.

Ahti

@SGaist
What example i don't see any. Btw you still hiring programmer ? :D

SGaist

"for example" in this case means "is one of the possibilities to solve your problem".

You misunderstood my signature ;-)