[Interest] QDateTime + QXmlStreamWriter on non-UTF8 compatible systems

[Thiago Macieira]

On sexta-feira, 22 de dezembro de 2017 19:30:39 -02 Scott Bloom wrote:
> Completely disagree.  The documentation clearly states the encoding is
> written out, and its not.  That is a problem.  The assumption is that the
> QString will be the final destination, that assumption is not documented,
> and not always true.

What would you have it write?

> If its not true, the client of the call, will potentially have a bug in
> their code, depending on how the QString is used later on.

Right. And hence the problem: if we don't know how you'll encode it, what 
would you have QXmlStreamWriter say the encoding is?

> Which is exactly what happened to me.  There is no explanation why a QBuffer
> vs QString would produce different XML.

There is an explanation. I've already said it multiple times. I understand 
you're frustrated and the documentation can be made clearer, but there is a 
very logical reason.

> For QA purposes, our XML generating classes, always had the internal
> "generate XML to a string" function so that we didn't have to create any IO
> in our unit testing.
> 
> I clearly see, to create proper XML that supports UTF-16 encoding, I needed
> to use a "Generate XML to an QIODevice*" methodology, since QIODevice
> create a proper XML file, and QString does not.. Not a problem, but
> completely undocumented.

Incorrect. The XML that QString generates *is* proper. It just doesn't say 
what the encoding is, since it's already in Unicode and requires no decoding. 
Wh'ats more, even if you convert to 8-bit, it's still valid and proper XML, 
since there is a default encoding for it, which you have to use (UTF-8) or you 
have to provide an external encoding mechanism. Writing that the encoding is 
"utf-8" when it's in QString form would be factually incorrect; writing the 
factually correct "utf-16" would be a hindrance if you tried to save to a file 
as 8-bit.

I repeat: the problem is not QXmlStreamWriter, but how you parsed that 
QString, including any transformations to 8-bit that you may have done. 

If you had fed it directly to QXmlStreamReader or QDomDocument::setContent, it 
should have decoded properly. If that didn't work, we have a bug and it needs 
to be fixed.

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center