[Interest] My experience porting to Qt5 (on OS X)

Konrad Rosenbaum konrad at silmor.de
Wed Sep 12 21:16:47 CEST 2012


On Wednesday 12 September 2012 19:16:29 Till Oliver Knoll wrote:
> Am 12.09.2012 um 17:47 schrieb Stephen Kelly <stephen.kelly at kdab.com>:
> > On Wednesday, September 12, 2012 16:20:01 Nikos Chantziaras wrote:
> >> Note that if you just do:
> >>   #include <Whatever>
> >> 
> >> then you can build with both Qt4 and Qt5.
> > 
> > If you do this, you also avoid mysterious linking errors resulting from
> > #include <QtWidgets/QWidget>
> Uhm... are you implying that when I
>   #include <QWidget>
> that qmake automagically figures out that it needs to link with
> "qtwidgets.dll" (or whatever the name), even I /don't/ have QT += widgets?
> Whereas when I
>   #include <QtWidgets/QWidget>
> it doesn't?!

No. It implies that with #include<QWidget> you get an outright compiler error 
when you miss QT+=widgets while the project can still be compiled with Qt4 
where it would be #include<QtGui/QWidget>.

> As for the "compile with Qt 4/5" part: I simply created a "qt5" Git branch.
> Once everything is stable there I merge everything back to "master". Works
> like a charm.

Another technique that I use:

To make the project link correctly to both Qt4 and Qt5 in the *.pro:
contains(QT_MAJOR_VERSION,"5") {
 QT += widgets printsupport

And in the rare cases that APIs changed in *.cpp files:
  QString subject=mycert.subjectInfo(QSslCertificate::CommonName)
#if QT_VERSION >= 0x50000

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