crash when delete QTreeWidgetItem*

[evgenM]

my code:

QList<QTreeWidgetItem*>::iterator itd = itemsToDelete.begin();
while (itd != itemsToDelete.end())
{
  QTreeWidgetItem* twi_ = *itd;
  if (!twi_->childCount())
  {
     cout <<twi_<<"-"<<twi_->childCount()<<endl; //log1
     cout <<twi_->text(0).toStdString()<<endl; //log2
     delete twi_;
     twi_ = 0;
     //twi_->setText(0, "ChangeText"); //if comment "delete twi_;" this line work
     cout <<"ok"<<endl;
     itd = itemsToDelete.erase(itd);
     cout <<"from List ok"<<endl;
   }
   else
       ++itd;
}

QList<QTreeWidgetItem*>::iterator itd = itemsToDelete.begin();
while (itd != itemsToDelete.end())
{
  QTreeWidgetItem* twi_ = *itd;
  if (!twi_->childCount())
  {
     cout <<twi_<<"-"<<twi_->childCount()<<endl; //log1
     cout <<twi_->text(0).toStdString()<<endl; //log2
     delete twi_;
     twi_ = 0;
     //twi_->setText(0, "ChangeText"); //if comment "delete twi_;" this line work
     cout <<"ok"<<endl;
     itd = itemsToDelete.erase(itd);
     cout <<"from List ok"<<endl;
   }
   else
       ++itd;
}

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now program log:
log1: 0x41617880-0 //normal - no children
log2: itemText // it's right too;

on line "delete twi_;" program crash (debugger mark this line too)
why it can be possible?

P.S my qt version 4.1.4
more precise: crashing only for non topLevelItems

[jacek]

QList<QTreeWidgetItem*>::iterator itd = itemsToDelete.begin();
...
QTreeWidgetItem* twi_ = *itd;
...
delete twi_;
...
itd = itemsToDelete.erase(itd); // <-- !

*itd points to a deleted object.

[evgenM]

*itd points to a deleted object.

so what? its not a problem (its just mean (*itd)=0).
btw log from "cout <<"ok"<<endl;" is not appear
and debugger said program crash on "delete twi_;"

[jacek]

so what? its not a problem

Well... yes, it doesn't matter in this case.

its just mean (*itd)=0.

No, it won't be set to 0.

debugger said program crash on "delete twi_;"

The problem is when you delete an item, you delete also all of its children, so some entries in itemsToDelete might become invalid and deleting a deleted pointer might cause a crash.

[evgenM]

The problem is when you delete an item, you delete also all of its children, .

if u check my code u will see the line
if (!twi_->childCount())
{
}
its special for this case

[jacek]

if u check my code u will see the line [...] its special for this case

True, I missed that.

How do you populate itemsToDelete?

[evgenM]

its not important
my list.count() == 1

i have found - it crash when destructor call twi_->parent();
its bug of inheritance (versions 4.1.1-4.1.4)

with 4.2.2 it work right (no crashing)

but i still have a problem because i need it under 4.1.4

[jacek]

i have found - it crash when destructor call twi_->parent();
its bug of inheritance (versions 4.1.1-4.1.4)

Is there a task tracker entry for that? I couldn't find anything relevant.

but i still have a problem because i need it under 4.1.4

Maybe you can use takeChild() or takeChildren() before deleting them to avoid the crash? As the last resort, you can always switch to QTreeView and a custom model.

[evgenM]

if u have a 4.1.4 version
u can try this:

QTreeWidgetItem* parent = new QTreeWidgetItem(treeWidget);
QTreeWidgetItem* child = new QTreeWidgetItem(0);
parent->addChild(child);
/////
now:
parent->child(0) == child;
but
child->parent() == 0;

//if QTreeWidgetItem* child = new QTreeWidgetItem(parent); --- its work right
--------------------------------------------------------------------------------------------

about takeChild();
yes i have trying
child->parent()->takeChild(child->parent()->indexOfChild(child));
same result

[jacek]

I've created a small test application and it doesn't crash (I use Qt 4.1.5).