Const pointer Map and Hash issue

astoffregen

I have a problem understanding QMap and QHash. I have already read that QMap provides a copy of the content and not a pointer / reference.

QMap<int, TextItem> items;
items.insert(0, TextItem());
items.insert(1, TextItem());

Do I still get a pointer to the content that I can use with this statement - it gives no compiler error?

TextItem a = items.value(0);
TextItem* b = &a;

This not

TextItem* c = &items.value(0);

Error is - a value from type const TextItem* could not use to initialize a entity of type TextItem*.

It works with QList, it must be a special feature of QMap.

Christian Ehrlicher

@astoffregen said in Const pointer Map and Hash issue:

TextItem* c = &items.value(0);

Apart from a possible compiler error this will result in a dangling pointer as the returned object is destroyed after the semicolon.

Wrt the error I would guess you use Qt5 where QMap::value() returns a const object as you can see in the documentation: https://doc.qt.io/qt-5/qmap.html#value