[CMake] Linker problems with compiling static QT lib with cmake

[Eric Noulard]

2010/7/29 Balske at t-online.de <Balske at t-online.de>:
>
> Hello,
>
> I am trying to compile a simple QT HelloWorld.cxx with cmake. I have a statically compiled qt installed as well as a non static version.
> What I want is a statically compiled HelloWorld. Cmake allows me to choose my static build of QT (using cmake-gui) by choosing the qmake
> binary in the static qt lib folder. When I do this it automatically changes the other entries like QT_LIBRARY_DIR to the static version. Looks great
> so far.
> Here the problems begin though:
> If I just generate my Makefile and make without adding CMAKE_EXE_LINKER_FLAGS "-static", everything seems to work and my HelloWorld binary ist beeing created. ldd reveals though that it has been linked against the shared version of the lib:
>
>> ldd ./HelloWorld
>> libQtGui.so.4 => /usr/lib/libQtGui.so.4 (0x00110000)
>> ...
>> ...
>
> This struck me as strange, as all entries in my generated CMakeCache.txt point to my static install of QT which certanly is nowhere near /usr/lib (in /usr/lib my nonstatic qt is installed). The result is, I have compiled a working HelloWorld binary which is linked against my nonstatic version of QT which cmake shouldn t even know about after changing the qmake binary path in the cmake configure process.
>
> This is not the real problem though, since I want to compile it with CMAKE_EXE_LINKER_FLAGS "-static". If I generate my Makefile with -static option, make throws the following linker error:
>
> canning dependencies of target HelloWorld
> [100%] Building CXX object CMakeFiles/HelloWorld.dir/HelloWorld.cxx.o
> Linking CXX executable HelloWorld
> /usr/bin/ld: cannot find -lQtGui
> collect2: ld returned 1 exit status
> make[2]: *** [HelloWorld] Error 1
> make[1]: *** [CMakeFiles/HelloWorld.dir/all] Error 2
> make: *** [all] Error 2
>
> Somehow the linker cannot find the QtGui module, which is in my statically compiled folder of QT under lib/libQtGui.a.
> Any ideas/solutions? I really have no idea at this point since everything looks fine in the cmake config/generation process.
> My CMakeLists.txt looks like this:
>
>
> PROJECT(HelloWorld)
>
> cmake_minimum_required(VERSION 2.6)
>
> FIND_PACKAGE(Qt4)
>
> IF(QT4_FOUND)
>        INCLUDE(${QT_USE_FILE})
> ELSE(QT4_FOUND)
> MESSAGE(FATAL_ERROR
> "Qt4 not found. Please set QT4_DIR.")
> ENDIF(QT4_FOUND)
>
> ADD_EXECUTABLE(HelloWorld HelloWorld.cxx )
> TARGET_LINK_LIBRARIES(HelloWorld QtGui)

Shouldn't you use:

TARGET_LINK_LIBRARIES(HelloWorld ${QT_QTGUI_LIBRARY})

note that from the FindQt4 module one can read:

"      Typical usage could be something like:

          find_package(Qt4 4.4.3 COMPONENTS QtCore QtGui QtXml REQUIRED )
          include(${QT_USE_FILE})
          add_executable(myexe main.cpp)
          target_link_libraries(myexe ${QT_LIBRARIES})"


more information with

cmake --help-module FindQt4


-- 
Erk
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