build problems with Qt and opencv on Windows

Question

I would like to create a gui application with Qt, using opencv on Windows XP. I used both Qt and opencv before, but never together. Long story short, I'm unable to get opencv work with Qt.

As on all the forums I searched there are just little pieces of information scattered around, usually with no answer, I summarize here all the steps I've taken.

1. Downloaded the Qt SDK (4.6.3) for Windows, and used it for some time, successfully.
2. Downloaded the opencv 2.3.1 megapack for Windows, complete with binaries. I managed to compile my Qt project including opencv successfully, but any opencv function call resulted in a crash. I read on some forums that the binaries in the Windows megapack don't support Qt, and I have to build opencv myself
3. I downloaded the latest version of CMake (2.8).
4. I downloaded the source of opencv from here: http://code.opencv.org/svn/opencv/branches/2.3/
5. I downloaded the source for the version of Qt I had (4.6.3)
6. I found my old version of visual Studio 2005
7. I created a VS2005 project with CMake, checking the support for Qt. (WITH_QT checked)
8. I built opencv in VS2005. It created most of the libraries, but not all. Highgui was among the failed ones. The problem: Qt\4.6.3\src\corelib\global\qconfig.h was not found. There was no qconfig.h at all in the source I downloaded! I found some templates qconfig-large.h, qconfig-small.h etc., so I renamed one of them to qconfig.h. Now I got a screen full of linker errors.
9. I downloaded the latest Qt source instead (4.8.1). Now there is a source file qbenchmark.h that includes QtTest/qbenchmarkmetric.h which cannot be found.
10. I gave up, and tried MinGW.
11. I downloaded the latest MinGW (2011.11.18)
12. I set CMake to generate a MinGW makefile, but I got the following error:

.

CMake Error at C:/Program Files/CMake 2.8/share/cmake-2.8/Modules/Platform/Windows-g++.cmake:1 (INCLUDE):
  include could not find load file:
C:/Program Files/CMake 2.8/share/cmake-2.8/Modules/Platform/Windows-gcc.cmake
Call Stack (most recent call first):
C:/Program Files/CMake 2.8/share/cmake-2.8/Modules/CMakeCXXInformation.cmake:59 (INCLUDE)

True, there is a Windows-g++.cmake file in the Modules/Platform directory, but it references Windows-gcc.cmake which does not exist!

Is there anyone who managed to build opencv with Qt support on Windows, and if yes, how?

Edit:

The problem is definitely with the Qt source. I managed to generate a MinGW makefile, and the build went all OK until it stopped in src/testlib/qtestsystem.h because there was an include for QtCore/qelapsedtimer.h which file is in a completely different directory! Does Qt release incomplete sources, or did I do something wrong?

Edit2

My torment continues. I cleaned everything and started anew. This time without even trying Visual Studio.

1. I downloaded the latest Qt libs with source (4.8.1)
2. I downloaded the latest MinGW (2011.11.18)
3. With CMake I successfully created a Makefile, and built it with MinGW. I got some shiny new libs (libopencv_core231, etv.). I was very happy, but how wrong I was to celebrate that soon!!
4. I downloaded the latest Qt SDK (strangely, it was 4.8.0, so I set Qt Creator to use the 4.8.1) and created a test program without opencv to see if it works. It worked!
5. I tried using opencv, just reading and displaying an image. It didn't work. exited with code -1073741511
6. I tried running the .exe directly, outside of Qt Creator. It complained of a missing libstdc++-6.dll
7. I did a search for it, and found on in my MinGW install (c:\mingw\bin, 958 KB), and one in my Qt install (c:\qt\mingw\bin, 793 KB) - this mingw came bundled with Qt.
8. I tried both, by copying them in the same folder where my .exe is, but neither worked. I got "The procedure entry point _ZNSt9exceptionD2Ev could not be located in the dynamic link library libstdc++-6.dll." with both. This was in debug, so I tried release, and I got a similar error, with some other entry point not found.
9. I searched the forums, and I found suggestions that I should link libstdc++ statically. I inserted -static-libgcc -static-libstdc++ at the lines QMAKE_LFLAGS = and QMAKE_LFLAGS_DEBUG = in the file c:\Qt\mkspecs\win32-g++\qmake.conf. This had no effect at all, even after restarting Qt Creator and rebuilding. If I don't copy the libstdc++-6.dll, it still requires it.

Of course, my simple test program without opencv runs from the exe without needing any libstdc++-6.dll, so that means my opencv build is responsible? I wanted to build opencv anew, but I cannot find any CMake settings referring to libstdc++ !

It might be a clue: When using one of the libstdc++-6.dll files, the error about a missing entrypoint mentions QtGui4.dll. I have a debug build, so it should be QtGui*d*4.dll, shouldn't it? Are there different libstdc++s for debug and release? Either way, I tried to build release, but it didn't work either, same error

Is there no single person on this planet who tried using Qt with QtCreator and opencv 2.3 together on Windows xp, and succeeded? From searching all the forums and Qt archives, I could not find anyone. I'm ready to do the development in Linux, but I'll need a Windows release sooner or later anyway.

_{I'm trying to resist the temptation of the dark side, which whispers into my ears to forget Qt, MinGW, g++, opencv and try to hack together something in Visual Basic. Oh, the horrors!}

Answer 1

Just FYI, I went basically through the same nightmare of combining Qt and OpenCV. This was my experience:

1. I downloaded the Qt SDK 4.7.4 with Qt Creator 2.4.1 and installed it, no problem.
2. I downloaded and installed OpenCV 2.4.2 and not knowing that it already came with MinGW...
3. I downloaded the MinGW compiler which of course had a different version than the one which came already with Qt
4. This completely messed up my CMake, even when I explicitly told CMake to use the Qt gcc.exe and g++.exe it also used some stuff from my freshly installed MinGW. Probably because I eagerly added every directory to my PATH variable. What a fool I was!
5. CMake was not able to generate any useful files, so I gave up and installed the OpenCV superpack, hoping this would make things easier. 6.I spent hours wondering, why Qt and OpenCV from the superpack didnt work properly together. I never quite understood. I had the same errors that other users describe here, like console programs crashing as soon as some OpenCV was included. The strange thing is, that I could start the executable manually from FileExplorer (I added all .dlls you could think of to the project folder: opencv_core242.dll, opencv_highgui242.dll, QtCore4.dll, QtGui4.dll and so on...) BUT I could not launch my little test program from within the Qt Creator environment.
6. I analysed if there was a problem with my DLLs using depends.exe and found out that even though I configured everything to be in DEBUG using the MinGW compiler, my program still tried to use QtCore4.dll and not QtCore4d.dll... So my best guess was, that it was mixing debug and release version.
7. I gave up using the superpack and again tried to use CMAKE first and then build OpenCV using the Qt MinGW version AND making sure to setup everything for Debug mode and enable the QT option. But no luck with that so far
8. I stopped using MinGW and switched over to MSVC2010, which works better. However I am still not able to debug the program since the MSVC2010 debugger engine seems to be missing. I dont really know how to manually add this but I am still working on it

So what I can definitely tell is that using Qt and OpenCV for somebody who has little experience is far from trivial!

Answer 2

You might have an easier time configuring Qt Creator with OpenCV. This post shows how to achieve that, step-by-step! It displays several screenshots to aid in the process too.

Answer 3

You should build OpenCV from source, as you already did, it is no hassle. Note that recent versions of OpenCV can be built with and w/o Qt. Highgui optionally uses Qt! It is your choice if you build with or without Qt.

I used Qt libraries together with OpenCV for long time now. I never went for the SDK, instead I used the libs which are built for corresponding VS version. See here: http://qt.nokia.com/downloads/downloads#qt-lib

You can have it for VS2008 and VS2010, but earlier versions are also available built for VS2005. Old versions of Visual Studio suck so hard, why use them anyway.

Then I never had problems pulling it together in a CMake project. It goes along the lines of:

find_package(OpenCV)
find_package(Qt4 ${VOLE_MINIMUM_QT_VERSION} COMPONENTS QtCore QtGui)
find_package(Qt4 ${VOLE_MINIMUM_QT_VERSION} COMPONENTS QtOpenGL)

...

qt4_wrap_cpp(moc_sources ${vole_module_moc_sources})
qt4_wrap_ui(uic_sources ${vole_module_ui_sources})
qt4_add_resources(rcc_sources ${vole_module_rcc_sources})

You know, the usual stuff.

Five man weeks later you may probably get it run under Windows, while under GNU/Linux it is three commands in the shell.