comments on KDE performance tips

[Simon Hausmann]

On Sat, Jan 18, 2003 at 02:16:42AM +0100, Roger Larsson wrote:
> 	Note: there will be only one string constant "hallo" stored in the program
> 	due to g++ option '-fmerge-constants' (default with -O2)
> That is why we have QConstString, as a bonus space is saved and that
> reduces time too. Less cache/pages misses.
> 	if (QConstString("hallo") == QConstString("hallo")) ... 
> 	// cheap constructors, no copy, comp ares only string storage location,
> 	// cheap destructors
> 
> 	const QConstString bye = "bye";  // cheap constructor with no copy
> 	if (bye == bye) ...  // only compares string storage location

Neither of these two QConstString usages do work nor are they
intended to work, because it expects raw QChar data and does not
provide a == operator because it privately inherits from QString.

If you operate on a raw array of QChar data like this you could use
it:

QChar *blah = ...
uint blahLength = ...
QChar *blubb = ...
uint blubbLength = ...

if ( QConstString( blah, blahLength ).string() == 
     QConstString( blubb, blubbLength ).string() ) {

But this is equal to a pointer comparison, except that it's slower,
for the temporary objects being created.

Simon