error LNK2001: unresolved external symbol "public: static struct QMetaObject .. from lib template

[kshegunov]

Three possibilities (in order of commonality):

1. You haven't specified the library for linking, or it is not found. See @SGaist's request and provide the project file so we can inspect it.
2. You and/or the library you're using is missing __declspec(dllimport) and/or __declspec(dllexport) for some reason. Make sure when compiling the library that the relevant macros are defined and list the symbols from the dll so you can make sure they're exported.
3. You're mixing incompatible compilers - the library is compiled with something e.g. mingw while you're trying to link with msvc (also versions matter).

[OPit]

This post is deleted!

[OPit]

myStream lib

TARGET = myStream
DESTDIR = D:/Dev/Programme/myLibs/myStream/lib/ms
TEMPLATE = lib
CONFIG += static thread
QT += widgets avwidgets

UI_HEADERS_DIR = build/ms/h
OBJECTS_DIR = build/ms/o
RCC_DIR = build/ms/qrc
MOC_DIR = build/ms/moc
INCLUDEPATH = D:/Dev/Programme/3rdparty/ms/include
LIBS = -LD:/Dev/Programme/3rdparty/ms/lib -lavformat

HEADERS += \
    ../../src/inputstream.h \
    ../../src/dateparser.h \
    ../../src/inputstreammanager.h \
    ../../src/inputstreamcontrol.h \
    ../../src/inputscenecontrol.h \
    ../../src/inputstreamvideo.h \
    ../../src/inputstreampegasus.h \
    ../../src/inputstreaminfo.h \
    ../../src/inputstreamimages.h \
    ../../src/stabilizer.h \
    ../../src/inputstreampreviewslider.h \
    ../../src/inputstreampreview.h
 

SOURCES += \     
    ../../src/inputstream.cpp \
    ../../src/dateparser.cpp \
    ../../src/inputstreammanager.cpp \
    ../../src/inputstreamcontrol.cpp \
    ../../src/inputscenecontrol.cpp \
    ../../src/inputstreamvideo.cpp \
    ../../src/inputstreampegasus.cpp \
    ../../src/inputstreamimages.cpp \
    ../../src/stabilizer.cpp \
    ../../src/inputstreampreviewslider.cpp \
    ../../src/inputstreampreview.cpp

Application .pro

QT += network widgets printsupport sql concurrent xml multimedia
QT += webenginewidgets
QT += avwidgets

TEMPLATE = app
DESTDIR = D:/Dev/Programme/AppTest/bin/ms
VERSION = 4.0

TARGET = AppTest
DEFINES += TARGET_NAME=\\\"$$TARGET\\\"

RC_FILE = ../../qrc/app.rc

UI_HEADERS_DIR = h
OBJECTS_DIR = o
RCC_DIR = qrc
MOC_DIR = moc

INCLUDEPATH = D:/Dev/Programme/3rdparty/ms/include

LIBS = -LD:/Dev/Programme/3rdparty/ms/lib \
        -lmyGUI \
        -lmyCharts \
        -lmyObject \
        -lmyStyleSheet \
        -lmyScene \
        -lmyStream -lswscale -lavformat -lavcodec -lavutil -lswresample -lws2_32 -lsecur32 \
        -lmyGraphics \
        -lmyCore \
        -lopencv_core400 \
        -lopencv_flann400 -ltbb -lzlib \
        -lgandalf \
        -lexiv2 -llibexpat \
        -llibcrypto \
        -lSMTPEmail \
        -lproj_5_2 \
        -lquazip

RESOURCES += \
    ../../qrc/resource.qrc

SOURCES += \
    ../../src/main.cpp \
    ../../src/core/interface.cpp \
    ../../src/core/core.cpp \
    ../../src/gui/maingui.cpp \
    ../../src/view/playerwidget.cpp \
    ../../src/view/sectionview.cpp \
    ../../src/view/inputstreampreview.cpp

HEADERS += \
    ../../src/core/interface.h \
    ../../src/core/core.h \
    ../../src/gui/maingui.h \
    ../../src/view/playerwidget.h \
    ../../src/view/sectionview.h \
    ../../src/view/frame.h \
    ../../src/view/inputstreampreview.h

[OPit]

@kshegunov

1. QtAV is imported in Qt config, so I think all is good for that (just add QT += avwidgets)
2. I have thinking about this problem but I don't know how to see if it's OK are not.
3. I've checked, and it's ok about that.

[kshegunov]

@OPit said in error LNK2001: unresolved external symbol "public: static struct QMetaObject .. from lib template:

1. QtAV is imported in Qt config, so I think all is good for that (just add QT += avwidgets)

Did you build that module yourself?

2. I have thinking about this problem but I don't know how to see if it's OK are not.

Firstly, use dependency walker to find out what the module links against, from there you could also see what kinds of symbols are exported. Then you can do the same for your library and see if everything matches.

3. I've checked, and it's ok about that.

How did you check? Where did you get the qtav module from, or did you compiled it yourself?

[OPit]

@kshegunov Yes, I've built myself the QtAv lib (because the last precompile binaries not use the last version of QtAv).
I've checked which compiler was used during compilation, and it was the same for each module.

NB : if I link the moc_inputstreampreview.obj file directly in my app, it works ?!?

LIBS += path/of/file/moc_inputstreampreview.obj

[OPit]

If I open QtAvWidget1.dll, I found the function :

?metaObject@VideoPreviewWidget@QtAV@@UEBAPEBUQMetaObject@@XZ

I can't read .lib file from dependency walker, how can I check these files ?

[SGaist]

In your build output, can you see whether the QtAV libraries are currently getting linked to your application ?

[OPit]

Hi,
I'm using QtCreator with visual studio compiler and I don't have a lot of informations during linking :

link /NOLOGO /DYNAMICBASE /NXCOMPAT /INCREMENTAL:NO /SUBSYSTEM:WINDOWS "/MANIFESTDEPENDENCY:type='win32' name='Microsoft.Windows.Common-Controls' version='6.0.0.0' publicKeyToken='6595b64144ccf1df' language='*' processorArchitecture='*'" /VERSION:4.0 /MANIFEST:embed /OUT:..\..\bin\ms\L2R_Video.exe @c:\Temp\L2R_Video.exe.4652.31672.jom
myStream.lib(moc_inputstreampreview.obj) : error LNK2001: symbole externe non résolu "public: static struct QMetaObject const QtAV::VideoPreviewWidget::staticMetaObject" (?staticMetaObject@VideoPreviewWidget@QtAV@@2UQMetaObject@@B)
..\..\bin\ms\L2R_Video.exe : fatal error LNK1120: 1 externes non résolus

But in my Makefile.Release file, the QtAv libs are well written :

LIBS          = /LIBPATH:D:\Dev\Programme\3rdparty\ms\lib 
D:\Dev\Programme\3rdparty\ms\lib\myStream.lib 
D:\Dev\Programme\3rdparty\ms\lib\swscale.lib 
D:\Dev\Programme\3rdparty\ms\lib\avformat.lib 
D:\Dev\Programme\3rdparty\ms\lib\avcodec.lib 
D:\Dev\Programme\3rdparty\ms\lib\avutil.lib 
D:\Dev\Programme\3rdparty\ms\lib\swresample.lib 
secur32.lib 
D:\Dev\Programme\3rdparty\ms\lib\myGraphics.lib 
ws2_32.lib shell32.lib advapi32.lib gdi32.lib User32.lib 
/LIBPATH:D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5WebEngineWidgets.lib 
D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5PrintSupport.lib 
D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5AVWidgets.lib 
D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5OpenGL.lib 
D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5Widgets.lib 
D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5Multimedia.lib 
D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5WebEngineCore.lib 
D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5Quick.lib 
D:\Dev\Environnement\ms\Qt\5.12.0\msvc2017_64\lib\Qt5AV.lib 
...

[SGaist]

Might be a silly question but are linking to libraries of the same type ? Meaning matching debug/release builds.

[OPit]

@SGaist said in error LNK2001: unresolved external symbol "public: static struct QMetaObject .. from lib template:

silly

Sadly it's not the problem ...

[aha_1980]

@OPit And both have the same architecture, i.e. 32 vs. 64 bit?

[kshegunov]

This:

@OPit said in error LNK2001: unresolved external symbol "public: static struct QMetaObject .. from lib template:

?metaObject@VideoPreviewWidget@QtAV@@UEBAPEBUQMetaObject@@XZ

Is very different from this:

?staticMetaObject@VideoPreviewWidget@QtAV@@2UQMetaObject@@B

The former is a method, the latter is a (global) variable. Please try again. Could you also provide the content of the moc file in question (the one that fixes the issue if linked with)?

[OPit]

@aha_1980 yes, the same architecture

@kshegunov this is a link to download the file (I can't upload from the forum) :
https://we.tl/t-bhEPIToZV2

Thanks.

[hskoglund]

Hi, perhaps it's a namespace problem, you could try changing to a using statement in your InputStreamPreview.h:

#include <QtAVWidgets/VideoPreviewWidget.h>

using namespace QtAV;

class InputStreamPreview : public VideoPreviewWidget
{
Q_OBJECT
...

[kshegunov]

@OPit said in error LNK2001: unresolved external symbol "public: static struct QMetaObject .. from lib template:

this is a link to download the file (I can't upload from the forum)

I'm sorry I wasn't clear. I meant the generated moc_XXX.cpp file. I have no tools to inspect the object file even if I wanted to because I work exclusively on Linux.

@hskoglund said in error LNK2001: unresolved external symbol "public: static struct QMetaObject .. from lib template:

Hi, perhaps it's a namespace problem, you could try changing to a using statement in your InputStreamPreview.h

A decent idea, but I don't think that's it. moc, while not too smart, does recognize namespaces and generates code accordingly. I do use them and everything links fine.

[OPit]

@kshegunov oh sorry, this is the cpp file.

https://we.tl/t-NXhNCGkSmc

[hskoglund]

Hi, do you have a moc_VideoPreviewWidget.cpp that's compiled using Qt 5.12? (The one in the link is built with Qt 5.9.1)

[OPit]

@hskoglund yes of course : https://we.tl/t-Uhhsre7Vzm

the problem is the same with version 5.9.1 or 5.12 (and also VS2017 or VS2015)

[hskoglund]

Hi, if you look in the .pro files above for your application and myStream.lib, both .pro files have a inputstreampreview.cpp and a inputstreampreview.h included. They are not located in the same directory (one pair is in ../../src/ and the other pair is in ../../src/view/) but if they have the same contents then maybe the linker gets confused when you build your app (together with your myStream.lib).

If they do not have the same contents (i.e. just a stroke of bad luck with the naming of your files) then rename one of the pairs. Otherwise, you could try building your app again but with only of the pairs, for example commenting out ../../src/view/inputstreampreview.cpp from the SOURCES section in your Application.pro file.