Warning in Qt 5: "Using QCharRef with an index pointing outside the valid range of a QString"

[AitorQt]

There is no error, just an unending list of warning which avoid me focusing in the real errors and warnings.

[Christian Ehrlicher]

@AitorQt said in Warning in Qt 5: "Using QCharRef with an index pointing outside the valid range of a QString":

There is no error

You're using an undocumented behavior which was removed in Qt6 so your app will crash with Qt6 and is using some undefined stuff in Qt5 so fix it. If you don't like it then don't ask how to fix it.

[mrjj]

Hi
Just to be sure I understand.
so this auto-extend feature
https://doc.qt.io/qt-5/qstring.html#operator-5b-5d
was removed and hence the warning ?

[AitorQt]

Now I understand @mrjj .
So, that means that using a so common operation like
QString str;
str[1] == ...
is deprecated? Then how is it supposed to be done? That has to do with the COW string to avoid expensive copies of strings, isn't it?

Thanks for the answer

[JonB]

@AitorQt
I had no idea that str[1] == ... or str[1] = ... beyond the string length was ever allowed, and would never have used it!

For your == question, what is wrong with if (str.length() > 1 && str[1] == ...)?

For =, what about something like str.resize(2, ' '); str[1] = ...;?

[AitorQt]

I have tested it.
Just adding the QString headers create the error. Doing just this.

#include <QString>
#include <QStringList>

int dummy = 1;

I run that and the warning appears 4 times! I suppose that the warning comes from the QStringList.h inside, probably the
library itself is doing it.

[JonB]

@AitorQt
? I have used Qt 5 for years without seeing such a warning, from its own header files? Your warning(s) should give the file/line number? Is that really inside their Qt code?

[AitorQt]

Ok, I have found it.

The error was trying to access an empty QString.

QString str = "";

str[0] == ...
that was the reason for the error

[Christian Ehrlicher]

@AitorQt said in Warning in Qt 5: "Using QCharRef with an index pointing outside the valid range of a QString":

That was the reason for the error

It was a warning, not an error.

Please mark the topic as solved then.

[AitorQt]

Yeah, done!