Qt 6 undefined reference to `qMain(int, char**)'

[HeJianglong]

@Christian-Ehrlicher said in Qt 6 undefined reference to `qMain(int, char**)':

Then simplify your code to a minimal example with a proper pro file.

I can compile correctly in qt6.6.0.

[Christian Ehrlicher]

Sometimes I wonder if people don't know what minimal means...

This works fine for me with Qt6.6.1/MinGW

#include <QApplication>

int main(int argc, char **argv)
{
    QApplication app(argc, argv);    
    return app.exec();
}

TEMPLATE = app
TARGET = tmp
INCLUDEPATH += .
QT += widgets
SOURCES += main.cpp

[HeJianglong]

@Christian-Ehrlicher said in Qt 6 undefined reference to `qMain(int, char**)':

Sometimes I wonder if people don't know what minimal means...

This works fine for me with Qt6.6.1/MinGW

#include <QApplication>

int main(int argc, char **argv)
{
    QApplication app(argc, argv);    
    return app.exec();
}

TEMPLATE = app
TARGET = tmp
INCLUDEPATH += .
QT += widgets
SOURCES += main.cpp

When I use the example you provided is normal.

I don't know how to troubleshoot this problem now, because some of my projects can be compiled, and some have this problem.

[Christian Ehrlicher]

Then simplify your projects until it works - a normal devleoper task.

[HeJianglong]

@Christian-Ehrlicher said in Qt 6 undefined reference to `qMain(int, char**)':

Then simplify your projects until it works - a normal devleoper task.

Thanks, I think I can get rid of the libraries I'm using and try again

[yeontak]

Did you solve it?

[changshou]

The same problem as you. Have you solved it? Please help me

[qt_john_doe]

There's a conflict between your code and a macro #define main qMain defined in include/QtGui/qwindowdefs.h
which is used to avoid a console window in a Qt project (as per https://stackoverflow.com/a/18553402). You can rename any variables in your code named main or reduce/rearrange includes as others have proposed.

[Q74r3wq-]

I have encountered the same error with a library I'm using (SDL2). I don't know whether it is the same library that is causing the issue, but for SDL2 I need to put up a macro to tell it that main() is being handled elsewhere (by QT):

#include <QApplication>
#define SDL_MAIN_HANDLED
#include <SDL2/SDL.h>

Hope it helps!

[QtFriend2024]

** MY SOLUTION **

I had this same issue with my QT Widgets project using Windows 11 host machine. I had upgraded my QT to 6.8.3 and this Error: undefined reference to `qMain(int, char)'** even though this wasn't the actual issue . Following my steps below, Qt Creator was able to highlight the actual issues for me to resolve and successfully build my project.

Steps to Resolve the Issue:

1. Create a new, most simple Qt Widgets project. Use the default mainwindow.h, mainwindow.cpp and mainwindow.ui
   with the project kit that you want to use
2. Run CMake
3. Build the project. It should build successfully
4. Open the CMakeLists.txt file
5. Utilize this new, simple CMakeLists.txt file as a template for your ORIGINAL project.
6. Modify the "template" CMakeLists.txt file to include your original project's resource file names where you see main.cpp, mainwindow.h, mainwindow.cpp, etc.
7. Modify the "template" CMakeLists.txt file to include the QT packages you are using (Core, Gui, or etc.)
8. Modify the "template" CMakeLists.txt file to include the target link libraries (refer to packages in previous step)
9. Build your original project
10. It should give you more specific, helpful errors to resolve (if there are any). For me, one of my *.cpp files #include Qt Serial Bus but I forgot to add it to CMakeLists.txt
11. Resolve errors
12. Rebuild. It built successfully for me.