Why does not QListWidget sort correctly?

[Qingshui Kong]

Hi everybody,

Could somebody give me some help?
I want to use QListWidget sortItems() function. I enabled sortingEnable. But I don't think the result is correct.
If I input items 1, 2, 1152, the result will be 1, 1152, 2. But I think the result should be 1, 2, 1152.

And if I test this code,
if("1" == "1152")
{
qDebug() << "'1' == '1152'";
}
else if("1" > "1152")
{
qDebug() << "'1' > '1152'";
}
else
{
qDebug() << "'1' < '1152'";
}
if("2" == "1152")
{
qDebug() << "'2' == '1152'";
}
else if("2" > "1152")
{
qDebug() << "'2' > '1152'";
}
else
{
qDebug() << "'2' < '1152'";
}
The output is
'1' < '1152'
'2' < '1152'

I think this is right.

So could somebody give me some advice?
Thanks in advance.

[Bonnie]

Do you know that you are comparing their memory addresses?
If you want to test the comparing, you should write like this

if(QString("1") == QString("1152"))

And the result is

'1' < '1152'
'2' > '1152'

That is how string comparision works.
It will not compare the number value...

One workaround to this is that do not use setText, but

item->setData(Qt::DisplayRole, 1151);

[Qingshui Kong]

@Bonnie Thank you very much.
You explained how string comparision works. That is correct. And I tested as you said. But in my opinion, I still think they should compare the length of each string. Let it alone.

At first my code is
ui->listWidget->addItem(QString::number(nNum));
ui->listWidget->sortItems();
It works. I can see the num in the listwidget.

But after I changed the code to
QListWidgetItem item;
item.setData(Qt::DisplayRole, nNum);
ui->listWidget->addItem(&item);
ui->listWidget->sortItems();
It doesn'tt work. I can't see anything.

[VRonin]

@Qingshui-Kong said in Why does not QListWidget sort correctly?:

But after I changed the code to
QListWidgetItem item;
item.setData(Qt::DisplayRole, nNum);
ui->listWidget->addItem(&item);
ui->listWidget->sortItems();

You were very close to the solution, you just have to create the QListWidgetItem on the heap instead of the stack otherwise it gets destroyed:

auto item = new QListWidgetItem;
item->setData(Qt::DisplayRole, nNum);
ui->listWidget->addItem(item);
ui->listWidget->sortItems();

[JonB]

@Qingshui-Kong said in Why does not QListWidget sort correctly?:

But in my opinion, I still think they should compare the length of each string.

Then you had better let the C++/Qt designers know you don't agree with the way string comparisons work.

[Qingshui Kong]

@VRonin Thanks. After I responded. I tried that. It worked.

[Qingshui Kong]

@JonB Maybe I just made a mistake. I just think I saw something like that.