[Qt-interest] How qt version sensitive are qt applications?

[Arnold Krille]

Hi,

On Saturday 27 March 2010 18:43:11 Robert Hairgrove wrote:
> Andreas Pakulat wrote:
> > On 27.03.10 16:09:16, Kārlis Repsons wrote:
> >> Considering the problem, lets say, Qt application was built for Qt
> >> version N1, but on the host system there is Qt version N2 -- in general,
> >> for what N1 and N2 will that application run on host? Is it really that
> >> N1==N2 for running?
> > Qt/Nokia guarantees that an app compiled with Qt4.x executes with
> > Qt4.x+1, that is it will start up and will generally work, but you may
> > find behavioural differences sometimes. In what way those affect your
> > app depends on which classes you've used.

Actually they say that an app compiled with Qt4.x works with libraries from 
Qt4.(x+y) where y is an unsigned int.

> > The other direction is only possible within patchlevel releases, so
> > compiling your app with Qt4.x.y and running it on Qt4.x.y-1 is possible,
> > but not running it on Qt4.x-1.
> This would mean that if I want my app to work with ANY Qt4 version, I
> must compile it with 4.0.0.

Yes.

> I thought that all major releases were
> backwards compatible?

Backwards compatible means that apps compiled/linked against the old lib from 
way back runs with the new version of the lib without a recompile.

> I.e., if someone had Qt 4.5.x installed, and I
> compiled my app with Qt 4.6.x, it should still work OK under the lesser
> 4.5.x but not under Qt 3.x.

No, not necessarily. New releases incorporate new classes and modules, how 
would you use a class introduced in Qt4.6 with a Qt installation of 4.2?
You can however make sure that your app works with all Qt4 version by using 
only Qt4.0.x on your developing (and linking) machine. But don't complain 
about missing features and un-fixed bugs...

Have fun,

Arnold
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