QListWidget deleting QListWidgetItem causes segmentaion fault - c++

Question

I have a C++ application where I am reading pcap file format and processing usb packets. For each packet, I would like to create a QListWidgetItem to which I am storing some data and then adding it to the QListWidget. Here is where the trouble begins. According to QListWidget documentation, after inserting item :
The list widget will take ownership of the item.
So what I thought is that its on QListWidget to delete all QListWidgetItems. The items are added fine, but when I close my app(I suppose thats when desctructor od QListWidget is called so he is calling desctructor of each QListWidgetItem) I get delete_scalar exception. According to call stack, deletion of some QListWidgetItem triggers it :
Snippet of my code (this function is being called for each packet in pcap file and is responsible for creating and adding items):
void ItemManager::ProcessPacket(QByteArray packetData)
{
const unsigned char* packet = (unsigned char*)packetData.data();
PUSBPCAP_BUFFER_PACKET_HEADER usbh = (PUSBPCAP_BUFFER_PACKET_HEADER)packet;
QListWidgetItem* item = new QListWidgetItem;
//set USBPCAP header to item
QByteArray usbhArray((const char*)packet, sizeof(USBPCAP_BUFFER_PACKET_HEADER));
item->setData(dataHolder->USBPCAP_HEADER_DATA, QVariant(usbhArray));
packet += sizeof(USBPCAP_BUFFER_PACKET_HEADER);
if (usbh->transfer == USBPCAP_TRANSFER_ISOCHRONOUS || usbh->transfer == USBPCAP_TRANSFER_CONTROL) //check for optional header data
{
int additionalDataSize = usbh->headerLen - sizeof(USBPCAP_BUFFER_PACKET_HEADER);
if (additionalDataSize > 0)
{
//set additional header data to item
QByteArray additionalDataArray((const char*)(packet), additionalDataSize);
item->setData(dataHolder->TRANSFER_OPTIONAL_HEADER, QVariant(additionalDataArray));
packet += additionalDataSize;
}
else
{
item->setData(dataHolder->TRANSFER_OPTIONAL_HEADER, QVariant()); //QVariant creates invalid QVariant, later i just need to check with QVariant::isValid()
}
}
else
{
item->setData(dataHolder->TRANSFER_OPTIONAL_HEADER, QVariant());
}
//set leftover data to item
QByteArray leftoverDataArray((const char*)packet, usbh->dataLength);
item->setData(dataHolder->TRANSFER_LEFTOVER_DATA, QVariant(leftoverDataArray));
listWidget->insertItem(listWidget->count(), item);
}
Calling of ProcessPacket function :
void ItemManager::ProcessFile(QString filename, bool liveReading)
{
if (fileReader.OpenNewFile(filename))
{
if (fileReader.ReadFileHeader())
{
while (!stopButtonClicked)
{
while (!fileReader.EndOfFile())
{
QByteArray packetData = fileReader.GetPacket();
if (!pauseButtonClicked)
{
ProcessPacket(packetData);
}
}
parent->Refresh(); //this is just calling QCoreApplication::processEvents();
if (!atBottomOfList)
{
listWidget->scrollToBottom();
}
if (liveReading)
{
Sleep(50);
}
else
{
return;
}
}
}
}
}
EDIT
I found out that this problem is happening only when appending to QListWidget through ItemManager class. In my main Q_OBJECT class USB_Packet_Analyzer(which holds QlistWidget that I am appending to) i have slot on_OpenButton_clicked() which looks like this :
void USB_Packet_Analyzer::on_OpenButton_clicked()
{
QString fil = QFileDialog::getOpenFileName(this, "Select source file", ".", "Pcap files (*.pcap)");
ItemManager manager(ui.listWidget,this);
manager.ProcessFile(fil, ui.liveCaptureRadioButton->isChecked());
}
where in ItemManager class constructor looks like this :
ItemManager::ItemManager(QListWidget* listWidget, USB_Packet_Analyzer* parent)
{
this->stopButtonClicked = false;
this->pauseButtonClicked = false;
this->atBottomOfList = false;
this->listWidget = listWidget;
this->parent = parent;
this->dataHolder = DataHolder::GetDataHolder();
}
Now, if I add items in on_OpenButton_clicked() slot and close the app, everything is fine. But when I create ItemManager instance and append items in that class, the error occurs. Could it be that I am not allowed to pass QListWidget* as parameter ?

Answer 1

You have to create a new item inside your loop. You must not reuse the pointer because no content is copied, only the pointer is stored within the QListWidget

Answer 2

To this day I am not completely sure what caused the error, but it was fixed after I modified USBPCAP structs which I were using. They use all kind of stuff like #pragma pack(1) , #pragma pack(push) and so on. It looks like I was missing some of those, which might result in some undefined behaviour while using them.