Qwt with CMake

[buster]

That got me a bit further, as the libries are now found. However, I get a page full of linking errors, that I cannot make sense of. The order I list the libraries in target_link_libraries doen't seem to make a difference, and the errors are the same whether I compile for Release or Debug:

[100%] Linking CXX executable plottapp
/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<QVariant>::metaType@Qt_6'
/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<bool>::metaType@Qt_6'
/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<QSize>::metaType@Qt_6'
  .
  .
  .
/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<QTime>::metaType@Qt_6'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/plottapp.dir/build.make:591: plottapp] Error 1
make[1]: *** [CMakeFiles/Makefile2:84: CMakeFiles/plottapp.dir/all] Error 2
make: *** [Makefile:136: all] Error 2
*** Failure: Exit code 2 ***

[100%] Linking CXX executable plottapp
/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<QVariant>::metaType@Qt_6'
/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<bool>::metaType@Qt_6'
/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<QSize>::metaType@Qt_6'
  .
  .
  .
/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<QTime>::metaType@Qt_6'
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/plottapp.dir/build.make:591: plottapp] Error 1
make[1]: *** [CMakeFiles/Makefile2:84: CMakeFiles/plottapp.dir/all] Error 2
make: *** [Makefile:136: all] Error 2
*** Failure: Exit code 2 ***

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[d_stranz]

Finding Qt6Widgets is supposed to also bring in the dependencies (Qt6Gui and Qt6Core) but maybe you need to add those. Those errors look like there is a low level Qt library that is not being linked in. Maybe try putting ${QWT} at the beginning of the link libraries list, followed by Charts, Widgets, Gui, and Core. I think that is the correct dependency order.

[buster]

I tried adding Qt6Gui and Qt6Core, and all kinds of reordering, but to no avail. I have no problem using Qt Charts, so the issue must be related to Qwt.

[d_stranz]

Are you sure you are building qwt against your Qt6 installation? Can you successfully use qwt in a project built with QtCreator? (I know these are "Have you checked to see if it is plugged in?" questions, but I've done things like this in the past, where I have had mismatched builds and nothing seems to work).

It is MOC that results in all of the QMetaType references so something could be wrong with your qwt build.

[buster]

I am not absolutely sure I am building Qwt corectly. I built Qwt thus:
/usr/bin/qmake qwt.pro
make
sudo make install

The strange thing is that all the examples supplied with Qwt works perfectly when build by QtCreator.

The file qwtconfig.pri starts of with:
QWT_VER_MAJ = 6
QWT_VER_MIN = 2
QWT_VER_PAT = 0
QWT_VERSION = $${QWT_VER_MAJ}.$${QWT_VER_MIN}.$${QWT_VER_PAT}
which looks correct to me.

I do not know if it is relevant, but qwt.pro has this information at the start:
lessThan(QT_MAJOR_VERSION, 5) {

lessThan(QT_MINOR_VERSION, 8) {
error(Qt >= 4.8 required.)
}
}

include( qwtconfig.pri )

The version 5 here probably refers to Qt 5.15.3 used by Kubuntu 22.04?
qmake --version
returns
QMake version 3.1
Using Qt version 5.15.3 in /usr/lib/x86_64-linux-gnu

I noticed that there is also qmake6, which returns:
qmake6 --version
QMake version 3.1
Using Qt version 6.2.4 in /usr/lib/x86_64-linux-gnu

So I tried:
make clean
/usr/bin/qmake6 qwt.pro
make
sudo make install
but the problem persists.

[d_stranz]

What do you see when you run this?

ldd -d -r libqwt.so

ldd -d -r libqwt.so

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Does it show dependencies on any of the Qt6 libraries?

How about opening the qwt.pro file in QtCreator and ensuring that you are building using a Qt6 kit?

I am afraid I am not really a linux developer, so this is getting to the limits of my knowledge and experience.

[buster]

I see:

ldd: ./libqwt.so: No such file or directory

ldd: ./libqwt.so: No such file or directory

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Q
I then created a link:

ln -s /usr/local/qwt-6.2.0/lib/libqwt.so.6.2.0 libqwt.so

ln -s /usr/local/qwt-6.2.0/lib/libqwt.so.6.2.0 libqwt.so

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but it made no difference. But output like

/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<QVariant>::metaType@Qt_6'

/usr/bin/ld: /usr/local/qwt-6.2.0/lib/libqwt.so: undefined reference to `QtPrivate::QMetaTypeInterfaceWrapper<QVariant>::metaType@Qt_6'

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indicated that the lib is found. It also indicates that qwt v. 6.2.0 is used, as well as Qt6, so it appears that there isn't a version mismatch. Also, I can build the qwt examples with Qt Creator, so libqwt.so seems to be OK.

[d_stranz]

Well. sorry, but I am at the end of my ideas. I think qmake creates a Makefile, right? (I use Visual Studio on Windows for all my development, which does not use Makefiles). Maybe take a look at one of those for your qwt examples and see if there is something in the linking that is missing from your CMakelists file. Otherwise, I don't know what else to suggest.

[buster]

Yes, cmake creates a makefile, but I don't find any clues there. There is a file called CMakeCache.txt, which includes:

Name  Value
QWT  /usr/local/qwt-6.2.0/lib/libqwt.so

Name  Value
QWT  /usr/local/qwt-6.2.0/lib/libqwt.so

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which is the correct path. Anyway, don't spend more time on this problem. I will keep scratching my head though. One thing I haven't thought about before: does qmake use hard-coded paths?

[d_stranz]

cmake creates a makefile

No, I meant qmake. Check the Makefile from that to see if there are any ideas about what could be wrong with the cmake configuration.