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Qt-interest Archive, February 2007
QList erase bug(qt4.2.2 in windows xp, vc 2003)?

Message 1 in thread

hi, all
      when invoking QList::erase, it should return  an iterator to the next item in the list (which may be end())  as document said, but when I run the following code, I don't get the correct result:
  QList<QString> strList;
  strList << "aa" << "bb" << "cc" << "dd";
  QList<QString>::iterator iter = strList.begin();
  QList<QString>::iterator iter_end = strList.end();
  while (iter != iter_end)
  {
    printf("value %s\n", (*iter).toLocal8Bit().data());
    if ( (*iter) == "dd" )
      iter =  strList.erase(iter);
    else
      iter++;
  }
it crashes, when I look at the iterator value, I find the iter value doesn't change when I run over iter = strList.erase(iter); even more, if you change (*iter) == "dd" to (*iter) == "cc", you will find "value dd" ouput twice. but if I use the std::list, everything is fine. 

Reimand
Message 2 in thread

reimand zhu schrieb:
> hi, all
> when invoking QList::erase, it should return an iterator to the next
> item in the list (which may be end()) as document said, but when I run
> the following code, I don't get the correct result:
> QList<QString> strList;
> strList << "aa" << "bb" << "cc" << "dd";
> QList<QString>::iterator iter = strList.begin();
> QList<QString>::iterator iter_end = strList.end();
> while (iter != iter_end)
> {
> printf("value %s\n", (*iter).toLocal8Bit().data());
> if ( (*iter) == "dd" )
> iter = strListerase(iter);
> else
> iter++;
> }
> it crashes, when I look at the iterator value, I find the iter value
> doesn't change when I run over iter = strList.erase(iter); even more, if
> you change (*iter) == "dd" to (*iter) == "cc", you will find "value dd"
> ouput twice. but if I use the std::list, everything is fine.

>From the documentation of QList::iterator:
"Multiple iterators can be used on the same list. However, be aware that
any non-const function call performed on the QList will render all
existing iterators undefined. If you need to keep iterators over a long
period of time, we recommend that you use QLinkedList rather than QList."

Best Regards / Mit freundlichen Grü?en
Rainer Wiesenfarth

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Message 3 in thread

reimand zhu wrote:
> hi, all
> when invoking QList::erase, it should return an iterator to the next 
> item in the list (which may be end()) as document said, but when I run 
> the following code, I don't get the correct result:
> QList<QString> strList;
> strList << "aa" << "bb" << "cc" << "dd";
> QList<QString>::iterator iter = strList.begin();
> QList<QString>::iterator iter_end = strList.end();
> while (iter != iter_end)
> {
> printf("value %s\n", (*iter).toLocal8Bit().data());
> if ( (*iter) == "dd" )
> iter = strListerase(iter);
> else
> iter++;
> }
> it crashes, when I look at the iterator value, I find the iter value 
> doesn't change when I run over iter = strList.erase(iter); even more, if 
> you change (*iter) == "dd" to (*iter) == "cc", you will find "value dd" 
> ouput twice. but if I use the std::list, everything is fine.
> 
> Reimand
When you erase an item, iterators pointing to later entries in the list 
become invalid. If you want to erase more than one item from a list, you 
should start at the end of the list and work forward.

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