[Development] Proposed API change: Change signature of QMessageHandler to use QString

[wolfgang.beck at nokia.com]

Before I would do such a change I would check if there are other projects in QT they install their own messaghandler.
I think they all need to change their code as well.
Maybe we should keep it as it is.

Cheers,
 WB

-----Original Message-----
From: development-bounces+wolfgang.beck=nokia.com at qt-project.org [mailto:development-bounces+wolfgang.beck=nokia.com at qt-project.org] On Behalf Of Koehne Kai (Nokia-MP/Berlin)
Sent: Friday, April 13, 2012 12:41 AM
To: thiago.macieira at intel.com; development at qt-project.org
Subject: Re: [Development] Proposed API change: Change signature of QMessageHandler to use QString


> -----Original Message-----
> From: development-bounces+kai.koehne=nokia.com at qt-project.org
> [mailto:development-bounces+kai.koehne=nokia.com at qt-project.org] On 
> Behalf Of ext Thiago Macieira
> Sent: Thursday, April 12, 2012 3:14 PM
> To: development at qt-project.org
> Subject: Re: [Development] Proposed API change: Change signature of 
> QMessageHandler to use QString
> 
> On quinta-feira, 12 de abril de 2012 08.17.37, kai.koehne at nokia.com wrote:
> > Hi,
> >
> > I'd like to get
> > https://codereview.qt-project.org/#change,22151,patchset=5
> > into 5.0/api_changes branch. It's one more change to the logging 
> > framework, specifically to the signature of QMessageHandler (new in 
> > 5.0, old QtMsgHandler is unchanged):
> >
> > void (*QMessageHandler)(QtMsgType, const QMessageLogContext &,
> const
> > char *);
> >
> > becomes
> >
> > void (*QMessageHandler)(QtMsgType, const QMessageLogContext &,
> const
> > QString &);
> 
> Maybe QChar *begin, int len?
> 
> Or QChar *begin, guaranteed to be NUL-terminated?

What's the advantage of having a QChar * in contrast to a QString? 

> > The reason is to avoid unnecessary string conversions, especially on 
> > Windows. E.g.
> >
> > qDebug() << "Hello World";
> >
> > will right now result in
> >
> > const char * -> QString conversion in QDebug::operator(const char *) 
> > (QString::fromAscii(), shouldn't this be QString::fromLatin1() btw?)
> 
> fromAscii() was correct in the sense of "from whatever the user used 
> in developing source code".

Just realized that nowadays fromAscii==fromLatin1. So it's really just a matter of taste.

> > QString -> const char * conversion in QDebug::~QDebug()
> > (QString::toLocal8Bit())
> > const char *-> QByteArray conversion in
> > qMessageFormatString() for the default message handler a QByteArray 
> > -> QString conversion in qWinMessageHandler() 
> > (QString::fromLocal8Bit)
> >
> > So we're converting from latin1 to utf16 to local8bit to utf16 :) 
> > The patch mitigates this somewhat by passing const QString & as 
> > argument to the message handler, instead of const char *.
> 
> I support this.
> 
> The message handler is new API and this change is not changing 
> compatibility with Qt 4.
>
> I assume you will do a final UTF16-to-local8bit if the user installed 
> a legacy 8- bit message handler.

Yes, that's already part of the patch.

> [...]

> --
> Thiago Macieira - thiago.macieira (AT) intel.com
>   Software Architect - Intel Open Source Technology Center
>      Intel Sweden AB - Registration Number: 556189-6027
>      Knarrarnäsgatan 15, 164 40 Kista, Stockholm, Sweden
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