Simple link of Qt6::Core to my libs using qtbase and FetchContent

Mesrine

Hi everyone,
I want to simple link my library to Qt::Core target after i have downloaded qtbase using

find_package(Qt6 QUIET COMPONENTS Core)
if(NOT Qt6_FOUND AND NOT TARGET Qt6::Core)
include(FetchContent)
FetchContent_Declare(
        qtbase
        GIT_REPOSITORY git://code.qt.io/qt/qtbase.git
        GIT_TAG 6.5.0
        )
FetchContent_MakeAvailable(qtbase)
endif()
target_link_libraries(qpow PUBLIC  Qt6::Core )

This work for simple version of libraries that do not need signal and slots.
But if i want my library to have signals and slots i have to add

set(CMAKE_AUTOMOC ON)

The later did not work for shared lib in mac and windows as you can see on the github actions

My question is do i need to have install qt(whatever that means) to be able to link to Qt6::Core(maybe i only need QbyteArray) to my lib in cmake,
or can i use only qtbase?

What is the procedure to be able to link an exported target of qtbase to my lib(without installing qt)?

How to use moc,rcc in my libraries from cmake like exported targets(no after i have installed qt).

Thank you for your time.

Christian Ehrlicher

@Mesrine said in Simple link of Qt6::Core to my libs using qtbase and FetchContent:

The later did not work for shared lib in mac and windows as you can see on the github actions

What does this mean?

If you want to create a shared library you have to properly export your classes you want to use from this library -> https://doc.qt.io/qt-6/sharedlibrary.html

Mesrine

thanks, @Christian-Ehrlicher
For that I am using
set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
I will try to explicitly set that macro.
Although is the ugliest thing i have see on c++ and do not think is the cause the linking is failing.

SGaist

Hi,

Are you sure qtbase is properly built when using FetchContent ?

In any case, it looks like overkill to build it rather than install the existing pre-built binaries.

Mesrine

@SGaist I am not sure, here it worked(the test run ok).

Normally my cmake looks before if Qt components are installed
if not it will download them and install it.
But downloading prebuilt binaries depends on the platform.
Ido not know how to install qt inside my github actions in a secure way. Do you know how to download the prebuilt binaries for the different platforms inside a github action?

SGaist

I haven't used it but there's an existing GitHub action for that.

Mesrine

@SGaist Thanks,
I will try this. But it will be nice to link qt ~~libraries~~ targets from cmake.

SGaist

You still can use cmake to build your project. You just have to point it to the Qt installation.

Mesrine

@Mesrine
This resulted on the same warning when configuring

-- Configuring done (96.9s)
CMake Warning (dev) in CMakeLists.txt:
  AUTOGEN: No valid Qt version found for target qpow.  AUTOMOC disabled.
  Consider adding:

    find_package(Qt6 COMPONENTS Core)

  to your CMakeLists.txt file.

and the same errors when linking for shared in mac and windows

[812/815] Linking CXX shared library lib/QtCore.framework/Versions/A/QtCore
[813/815] Linking CXX shared library _deps/qcurlp81-build/libqcurlp81.dylib
[814/815] Linking CXX shared library _deps/qb1t6-build/libqb1t6.dylib
[815/815] Linking CXX shared library libqpow.dylib
FAILED: libqpow.dylib 
: && /Applications/Xcode_14.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ -DNDEBUG -O2 -isysroot /Applications/Xcode_14.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk -mmacosx-version-min=12.6 -dynamiclib -Wl,-headerpad_max_install_names  -o libqpow.dylib -install_name @rpath/libqpow.dylib CMakeFiles/qpow.dir/qpow.cpp.o -F/Users/runner/work/_temp/build/lib -Wl,-rpath,/Users/runner/work/_temp/build/_deps/qb1t6-build -Wl,-rpath,/Users/runner/work/_temp/build/_deps/qcurlp81-build -Wl,-rpath,/Users/runner/work/_temp/build/lib  _deps/qb1t6-build/libqb1t6.dylib  _deps/qcurlp81-build/libqcurlp81.dylib  lib/QtCore.framework/Versions/A/QtCore  -framework IOKit  -framework DiskArbitration && :
Undefined symbols for architecture x86_64:
  "qiota::qpow::nonceFinder::nonce_found(unsigned long long)", referenced from:
      QtPrivate::QFunctorSlotObject<qiota::qpow::nonceFinder::calculate(QByteArray const&)::$_0, 1, QtPrivate::List<unsigned long long>, void>::impl(int, QtPrivate::QSlotObjectBase*, QObject*, void**, bool*) in qpow.cpp.o
  "qiota::qpow::nonceFinder::nonce_not_found()", referenced from:
      QtPrivate::QFunctorSlotObject<qiota::qpow::nonceFinder::calculate(QByteArray const&)::$_1, 0, QtPrivate::List<>, void>::impl(int, QtPrivate::QSlotObjectBase*, QObject*, void**, bool*) in qpow.cpp.o
  "qiota::qpow::WorkerThread::found_nonce(unsigned long long)", referenced from:
      qiota::qpow::WorkerThread::doWork(unsigned long long const&) in qpow.cpp.o
      qiota::qpow::nonceFinder::calculate(QByteArray const&) in qpow.cpp.o
  "qiota::qpow::WorkerThread::staticMetaObject", referenced from:
      qiota::qpow::nonceFinder::calculate(QByteArray const&) in qpow.cpp.o
  "vtable for qiota::qpow::nonceFinder", referenced from:
      qiota::qpow::nonceFinder::nonceFinder() in qpow.cpp.o
      qiota::qpow::nonceFinder::nonceFinder() in qpow.cpp.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for qiota::qpow::WorkerThread", referenced from:
      qiota::qpow::nonceFinder::calculate(QByteArray const&) in qpow.cpp.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
Error: Process completed with exit code 1.

The missing symbols are classes that inherit from QObject and its signals .
The fact that there is not linking problem on static builds for windows, mac, and for static and shared build for linux, tell me there is no symbol without definition on my code.
And the linking problem is relate with the moc produced object.

SGaist

As suggested above, did you point cmake to your installation of Qt 6 ?

The automoc issue means that the files are not generated for your QObject based classes.

Mesrine

@SGaist I understand what you say, but as initially stated on my question i do not want to install Qt.
I would like to find a pakage using cmake like

find_package(Qt6 QUIET COMPONENTS Core)

If is not present on the system make it available by using

FetchContent_Declare(
        qtbase
        GIT_REPOSITORY git://code.qt.io/qt/qtbase.git
        GIT_TAG 6.5.0
        )
FetchContent_MakeAvailable(qtbase)

This a very reasonable design of cmake packages and targets.
Ideally this will configure moc and rcc and built them at compilation time, to them use the moc executable with the QObject macros in my source code and finaly compile my library.

So again my question is this can be done at the current state of qt6.5.0 or not?
If can be done do anyone have a reference?

Mesrine

@Mesrine
Regarding the warning

-- Configuring done (96.9s)
CMake Warning (dev) in CMakeLists.txt:
  AUTOGEN: No valid Qt version found for target qpow.  AUTOMOC disabled.
  Consider adding:

    find_package(Qt6 COMPONENTS Core)

It seems one needs to set QT_VERSION_ variables to enable autogen according to this
if set

...
FetchContent_MakeAvailable(qtbase)
set_directory_properties(PROPERTIES
                              Qt6Core_VERSION_MAJOR 6
                              Qt6Core_VERSION_MINOR 5
                             Qt6Core_VERSION_PATCH 0)

CMake complains like

CMake Error: AUTOMOC for target qpow: The "moc" executable "/root/build/libexec/moc" does not exist.

Cmake use the moc executable at configuration time?
But the warning also occurs on linux (where it compiles without problems).

SGaist

I don't know how that function builds dependencies so I can't answer that. One of the issues I see is the amount of dependencies required to build Qt itself before building your own application, the fact that you would usually use the configure script to setup the build before using cmake to start the build. And finally, does that part end up in some cache ? Otherwise it means that you will rebuild qtbase everytime your CI runs which seems like a waste of electricity and time.

Mesrine

@SGaist when using the qt install action, windows and mac compiles ok, for ubuntu i get the following error when building my library and the test executable

[1/8] Automatic MOC and UIC for target qb1t6
[2/8] Building CXX object CMakeFiles/qb1t6.dir/qb1t6_autogen/mocs_compilation.cpp.o
[3/8] Building CXX object CMakeFiles/qb1t6.dir/qb1t6.cpp.o
[4/8] Linking CXX shared library libqb1t6.so
[5/8] Automatic MOC and UIC for target tip5
[6/8] Building CXX object tests/CMakeFiles/tip5.dir/tip5_autogen/mocs_compilation.cpp.o
[7/8] Building CXX object tests/CMakeFiles/tip5.dir/tip5.cpp.o
[8/8] Linking CXX executable tests/tip5
FAILED: tests/tip5 
: && /usr/bin/c++ -O3 -DNDEBUG  tests/CMakeFiles/tip5.dir/tip5_autogen/mocs_compilation.cpp.o tests/CMakeFiles/tip5.dir/tip5.cpp.o -o tests/tip5  -Wl,-rpath,/home/runner/work/_temp/build:/home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib  libqb1t6.so  /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0 && :
/usr/bin/ld: warning: libicui18n.so.56, needed by /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0, not found (try using -rpath or -rpath-link)
/usr/bin/ld: warning: libicuuc.so.56, needed by /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0, not found (try using -rpath or -rpath-link)
/usr/bin/ld: warning: libicudata.so.56, needed by /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0, not found (try using -rpath or -rpath-link)
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucol_open_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `UCNV_FROM_U_CALLBACK_SUBSTITUTE_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `u_strToLower_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_getStandardName_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_getToUCallBack_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_cbFromUWriteUChars_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_toUCountPending_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_clone_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `UCNV_TO_U_CALLBACK_SUBSTITUTE_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_getName_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_fromUCountPending_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `uenum_next_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_open_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_setToUCallBack_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucol_setAttribute_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `u_strToUpper_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_setFromUCallBack_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_getTimeZoneDisplayName_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_openCountryTimeZones_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_fromUnicode_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_open_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_openTimeZones_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_inDaylightTime_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `uenum_close_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_close_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_cbToUWriteUChars_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_openTimeZoneIDEnumeration_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_reset_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_getDSTSavings_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_getDefaultTimeZone_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_toUnicode_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_getFromUCallBack_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_setMillis_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucol_strcoll_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_close_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucol_close_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucol_getSortKey_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucnv_getMaxCharSize_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_getTimeZoneTransitionDate_56'
/usr/bin/ld: /home/runner/work/Qb1t6/Qt/6.5.0/gcc_64/lib/libQt6Core.so.6.5.0: undefined reference to `ucal_get_56'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
Error: Process completed with exit code 1.

You can see the Cmakelists.txt here
Do i need to manually install those libraries for every platform?
when trying to install by

sudo apt-get install ninja-build cmake build-essential libgl1-mesa-dev libicu-dev

it says:

libicu-dev is already the newest version (70.1-2).

SGaist

@Mesrine which version of Ubuntu would that be ?

Mesrine

@SGaist Distributor ID: Ubuntu
Description: Ubuntu 22.04.2 LTS
Release: 22.04
Codename: jammy

Mesrine

@Mesrine
I was using the action like

- name: Install Qt
        uses: jurplel/install-qt-action@v3
        with:
          version: '6.5.0'
          archives: 'qtbase'

but if you change to

- name: Install Qt
        uses: jurplel/install-qt-action@v3
        with:
          version: '6.5.0'

it works

SGaist

I suspect that the libraries are installed along another module but I currently don't know which one.