[Interest] QVariantMap: constEnd() not equal to end()?

[Harri Porten]

On Fri, 20 Mar 2015, Aleksandr Mezin wrote:

> Table::const_iterator i(table.constFind(name));
> if (i != table.end()) {
>     ...
> }
> 
> Table is a typedef for QHash<...>
> 
> This code doesn't work as I expect with Qt 5.4.1 MSVC 2013.
> The "if" is never entered, even when 'name' isn't found in the table.
> But it starts to work after replacing "end()" with "constEnd()".
> So, I guess, end() isn't equal to constEnd()? Is it an intended behavior?

Let's say it's undefined behavior. end() and constEnd() could return the 
same iterator. But it depends on the implementation as well as the state 
(shared or detached) of the QHash instance. Better don't mix the const and 
non-const iterator functions.

See

  http://doc.qt.io/qt-5/containers.html#implicit-sharing-iterator-problem

(and the whole chapter) for more details.

Harri.