Warning "allocating an unneeded temporary container" when getting the index of a QMap key

Donald Duck

I'm trying to get the index of a key in a QMap. I have this code:

map.keys().indexOf(someKey);

This works fine, but I get a warning saying "allocating an unneeded temporary container", which suggests that there is a better way to do this. The warning doesn't say what I should do instead though. If searched for how to get the index of a QMap key, but I haven't found anything interesting.

How do I fix this warning?

JonB

@Donald-Duck
Since your keys are QString you could save yourself some time/hassle with comboBox.setCurrentText(someKey) :)

Christian Ehrlicher

@Donald-Duck said in Warning "allocating an unneeded temporary container" when getting the index of a QMap key:

How do I fix this warning?

By reading the docs. An an index of a map is nothing which you should work with.

Donald Duck

@Christian-Ehrlicher The docs don't seem to have anything to get the index. The method you linked to gives the key of a given value. I already have the key, and I need the index associated with it as a number.

If you need to know why I need this, it's because I have a QComboBox which is supposed to show values corresponding to the keys:

QMap<QString, NotImportant> map;
QComboBox comboBox;
foreach(const QString &key, map.keys()){
    comboBox.addItem(key);
}
comboBox.setCurrentIndex(map.keys().indexOf(someKey));    //This is the line that gives the warning

Since the setCurrentIndex method takes an int, I need the index associated with the key, not the key itself. I could always copy map.keys() into a QList, but that seems unnecessary.

Christian Ehrlicher

Again: you should and must not use an index of a map since this is nothing a map can be described with.
Since you already create a container you can use this:

const auto keys = map.keys();
comboBox.addItems(keys);
comboBox.setCurrentIndex(keys.indexOf(someKey));

JonB

@Donald-Duck
Since your keys are QString you could save yourself some time/hassle with comboBox.setCurrentText(someKey) :)