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I have a Qt project that uses OpenGL and compiles fine with Qt 5.4.0. Today I upgraded my Qt to 5.5.0 and my project stopped compiling. It throws a lot of unresolved external symbol errors as you can see here:

link /NOLOGO /DYNAMICBASE /NXCOMPAT /DEBUG /SUBSYSTEM:WINDOWS "/MANIFESTDEPENDENCY:type='win32' name='Microsoft.Windows.Common-Controls' version='6.0.0.0' publicKeyToken='6595b64144ccf1df' language='*' processorArchitecture='*'" /MANIFEST:embed /OUT:debug\UI.exe @C:\Users\DWilches\AppData\Local\Temp\UI.exe.376.5500.jom
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glBegin@4 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::paintGL(void)" (?paintGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glClearDepth@8 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::initializeGL(void)" (?initializeGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glColor3f@12 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::paintGL(void)" (?paintGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glColor4f@16 referenced in function "private: void __thiscall UIOpenGLVisualizer::PaintScene(void)" (?PaintScene@UIOpenGLVisualizer@@AAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glEnd@0 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::paintGL(void)" (?paintGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glFrustum@48 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::paintGL(void)" (?paintGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glInitNames@0 referenced in function "public: void __thiscall UIOpenGLVisualizer::NewSelectionPerformed(void)" (?NewSelectionPerformed@UIOpenGLVisualizer@@QAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glLineStipple@8 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::initializeGL(void)" (?initializeGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glLoadIdentity@0 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::initializeGL(void)" (?initializeGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glLoadName@4 referenced in function "public: void __thiscall UIOpenGLVisualizer::NewSelectionPerformed(void)" (?NewSelectionPerformed@UIOpenGLVisualizer@@QAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glMatrixMode@4 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::initializeGL(void)" (?initializeGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glOrtho@48 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::initializeGL(void)" (?initializeGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glPointSize@4 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::initializeGL(void)" (?initializeGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glPushName@4 referenced in function "public: void __thiscall UIOpenGLVisualizer::NewSelectionPerformed(void)" (?NewSelectionPerformed@UIOpenGLVisualizer@@QAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glRenderMode@4 referenced in function "public: void __thiscall UIOpenGLVisualizer::NewSelectionPerformed(void)" (?NewSelectionPerformed@UIOpenGLVisualizer@@QAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glRotatef@16 referenced in function "public: void __thiscall UIOpenGLVisualizer::NewSelectionPerformed(void)" (?NewSelectionPerformed@UIOpenGLVisualizer@@QAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glScalef@12 referenced in function "public: void __thiscall UIOpenGLVisualizer::NewSelectionPerformed(void)" (?NewSelectionPerformed@UIOpenGLVisualizer@@QAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glSelectBuffer@8 referenced in function "public: void __thiscall UIOpenGLVisualizer::NewSelectionPerformed(void)" (?NewSelectionPerformed@UIOpenGLVisualizer@@QAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glTranslatef@12 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::paintGL(void)" (?paintGL@UIOpenGLVisualizer@@UAEXXZ)
UIOpenGLVisualizer.obj : error LNK2019: unresolved external symbol __imp__glVertex3f@12 referenced in function "public: virtual void __thiscall UIOpenGLVisualizer::paintGL(void)" (?paintGL@UIOpenGLVisualizer@@UAEXXZ)
debug\UI.exe : fatal error LNK1120: 20 unresolved externals
jom: C:\Users\DWilches\Desktop\3DIA\VolumeSelector\VVSIT\build-VVSIT-Desktop_Qt_5_5_0_MSVC2013_32bit-Debug\UI\Makefile.Debug [debug\UI.exe] Error 1120
jom: C:\Users\DWilches\Desktop\3DIA\VolumeSelector\VVSIT\build-VVSIT-Desktop_Qt_5_5_0_MSVC2013_32bit-Debug\UI\Makefile [debug] Error 2
21:35:43: The process "C:\ProgramFiles\Qt\Qt5.5.0\Tools\QtCreator\bin\jom.exe" exited with code 2.
Error while building/deploying project VVSIT (kit: Desktop Qt 5.5.0 MSVC2013 32bit)
When executing step "Make"

I have not modified the .pro files between one and other version of Qt. And my .pro also has the line that says:

QT += opengl

What could be wrong ?

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    You need to pass opengl32.lib to link. You're using a response file, so you'll want to put it there instead of the command-line, and I don't know how to use your particular tool to control the response file, but opengl32.lib is the import library where those functions are found. Commented Jul 26, 2015 at 3:42
  • Yes, thanks, I added -lopengl32 and now it works. I wonder why now it is necessary with this new version of Qt, while before it seemed to be done automatically by: QT += opengl. Could you add this as an answer ? Commented Jul 26, 2015 at 3:48
  • I have no clue what QT += opengl does or doesn't do in the different versions, so any answer I write wouldn't be very complete. Why don't you write a self-answer showing how/where you added that -lopengl32 to make it play nicely with the Qt build process? Commented Jul 26, 2015 at 3:49

1 Answer 1

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13

As exposed by @Ben-Voigt in the comments above, I had to explicitly instruct Qt to link against opengl32, so I added the following in my .pro:

LIBS += -lopengl32

I'm not sure why there is a change in behaviour in Qt 5.5.0 as that line was unnecessary in previous versions, but well, it solves the problem.

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5 Comments

If I had to guess, there was a hard coded check inside qt to replace opengl with the proper system-specific library, and somehow that got broken in 5.5. However I don't use qt (or opengl) so it's just a guess. I'd report this as a bug on their forums.
@Blindy: There's no such thing as a system specific library, when it comes to OpenGL (yes I do know, that in Linux the vendor proprietary drivers install their own libGL.so). The ABIs of the OSs where OpenGL is supported pinned down and any DLL/SO that follows those ABIs will link at runtime with your program just fine (assuming the program itself adheres to the ABI as well).
@Blindy: I think something like what you said is what happened, check this: blog.qt.io/blog/2015/07/01/qt-5-5-released , specially: Using OpenGL on Windows has always been somewhat problematic as good drivers are not available in all installations by default. Qt 5.5 helps solve this problem by switching dynamically between using the OpenGL driver or the ANGLE emulation layer implementing OpenGL on top of DirectX.
@datenwolf, not sure what your point is -- Linux typically uses libGL, Windows opengl32.lib, those are system-specific names. Of course you're probably just arguing to hear yourself speak so you can ignore that. @Mondkin yeah it kinda made sense. That's good, it means that chances are good it will be fixed in a patch or the next version.
@Blindy: Oh, I took your comment as "in Linux every OpenGL driver brings his how libGL.so" and some people mistake that for that programs must be linked to that specific libGL.so or use dlopen/dlsym to resolve the symbols (in ancient times this was indeed the case, but then the LSB pinned down the ABI requirements and ever since this has not been a problem). Anyway, when we're at system specifics, then there's -framework OpenGL on MacOS X; however all of that should be abstracted away in Qt's qmake (it definitely is in CMake's FindOpenGL.cmake module).

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