Re: QCString construction

On Saturday 10 February 2007 01:43, David Faure wrote:
> I was debugging today the memory consumption by kmail
(qt3) when sending
> signed emails with large attachments. Among other
things, I noticed many
> QCString(const char*) constructions in kmail, like:
QCString
> KMMessage::asString() const {
>    return asDwString().c_str();
> }
> and
> messagecomposer.cpp: mEncodedBody =
dwPart->AsString().c_str();

The fastest string copy is not doing it at all...
Why is code like this necessary? Why returning a low level
c_str?
If it is why does it have to be in a hot path?

I have been guilty of optimizing code that is rarely used
resulting in
- less readable code
- more prone to errors
- harder to optimize later
- for very little real world gain...

(I will check your patches)

/RogerL
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On Saturday 10 February 2007, Roger Larsson wrote:
> On Saturday 10 February 2007 01:43, David Faure wrote:
> > I was debugging today the memory consumption by
kmail (qt3) when sending
> > signed emails with large attachments. Among other
things, I noticed many
> > QCString(const char*) constructions in kmail,
like: QCString
> > KMMessage::asString() const {
> >    return asDwString().c_str();
> > }
> > and
> > messagecomposer.cpp: mEncodedBody =
dwPart->AsString().c_str();
> 
> The fastest string copy is not doing it at all...
I know that. And I'm considering making more use of DwString
in the affected kmail code,
to avoid going via QCString.

> Why is code like this necessary? 
Because of the use of mimelib in kmail.

> Why returning a low level c_str? 
That's what I fixed.

> If it is why does it have to be in a hot path?
What do you want me to say? kmail mixes two string classes
because of the use of mimelib.

> I have been guilty of optimizing code that is rarely
used resulting in
Rarely used?? I'm only looking at the places where I found
kmail to spend a lot
of time while sending large emails. I know all about the
dangers of premature
or misguided optimization, this is really about making the
bottlenecks faster, not just
any string copying I found.

-- 
David Faure, faurekde.org, sponsored by Trolltech to work on
KDE,
Konqueror (http://www.konqueror.org
), and KOffice (http://www.koffice.org).
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