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

HeJianglong

I came across a problem and I have no idea what is causing it.

I have a project with some library + a number of example apps and tests linking to it and I'm using QMake as build system.
When I'm using the combo:

Qt 6.6.1
MinGW compiler

I get undefined reference to `qMain(int, char**)' when building the applications.
Any idea what I am doing wrong here?

error: D:\Qt\6.6.1\mingw_64\lib\libQt6EntryPoint.a(qtentrypoint_win.cpp.obj):C:/Users/qt/work/qt/qtbase/src/entrypoint/qtentrypoint_win.cpp:50: undefined reference to `qMain(int, char**)'

Christian Ehrlicher

Please show your main.cpp and CMakeLists.txt

HeJianglong

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

Please show your main.cpp and CMakeLists.txt

The main function looks like this:

I'm using .pro files, which are a lot of stuff

Christian Ehrlicher

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

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.

A '.pro' file looks like this :

QT += core gui network serialport xml concurrent sql multimedia multimediawidgets qml svg printsupport

greaterThan(QT_MAJOR_VERSION, 5){
QT += core5compat
}

greaterThan(QT_MAJOR_VERSION, 4){
QT += widgets
TARGET_ARCH=$${QT_ARCH}
}else{
TARGET_ARCH=$${QMAKE_HOST.arch}
}

lessThan(QT_MAJOR_VERSION, 6) {
win32 {
QT += axcontainer
}
}

DEFINES += QT_DEPRECATED_WARNINGS

CONFIG += c++17 warn_off debug_and_release object_parallel_to_source

CONFIG += resources_big

QMAKE_CXXFLAGS += -Wa,-mbig-obj

qtHaveModule(opengl): QT += opengl

TEMPLATE = app
MOC_DIR = $${OUT_PWD}/temp/moc
RCC_DIR = $${OUT_PWD}/temp/rcc
UI_DIR = $${OUT_PWD}/temp/ui
OBJECTS_DIR = $${OUT_PWD}/temp/obj

DESTDIR = $${INSTALL_PATH}

TRANSLATIONS += uc_zh_CN.ts
TRANSLATIONS += uc_en_US.ts

Default rules for deployment.

qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

resources file

RESOURCES += ../x3res.qrc

win32:LIBS += -lwinmm

#####################################################

3rd-party

#####################################################

ads

#INCLUDEPATH += ../3rd-party/ads
#DEPENDPATH += ../3rd-party/ads

acss

#INCLUDEPATH += ../3rd-party/acss
#DEPENDPATH += ../3rd-party/acss
DEFINES += "STYLES_DIR=$$PWD/../styles"

quazip

INCLUDEPATH += $$PWD/../3rd-party/quazip/include
DEPENDPATH += $$PWD/../3rd-party/quazip/include
DEFINES += QUAZIP_STATIC

LIBS += -L$$PWD/../3rd-party/quazip/lib -lquazip

#protobuf
#DEFINES += PROTOBUF_USE_DLLS
LIBS += -L$$PWD/../3rd-party/protobuf/lib -llibprotobuf
INCLUDEPATH += $$PWD/../3rd-party/protobuf/include
DEPENDPATH += $$PWD/../3rd-party/protobuf/include

#Log4Qt
DEFINES += LOG4QT_STATIC #静态编译的LOG4QT必须定义该宏才能正常使用
LIBS += -L$$PWD/../3rd-party/Log4qt/lib -llog4qt
INCLUDEPATH += $$PWD/../3rd-party/Log4qt/include
DEPENDPATH += $$PWD/../3rd-party/Log4qt/include

FFMPEG

LIBS += -L$$LIBRARY_PATH -lavutil -lavformat -lavcodec -lavdevice -lavfilter -lswresample -lswscale
INCLUDEPATH += $$PWD/../3rd-party/ffmpeg/include
DEPENDPATH += $$PWD/../3rd-party/ffmpeg/include

fft

LIBS += -L$$PWD/../3rd-party/fftw/lib -lfftw3
INCLUDEPATH += $$PWD/../3rd-party/fftw/include
DEPENDPATH += $$PWD/../3rd-party/fftw/include

QZXing3

DEFINES += ENABLE_ENCODER_GENERIC

LIBS += -L$$PWD/../3rd-party/qzxing3/lib -lQZXing3
INCLUDEPATH += $$PWD/../3rd-party/qzxing3/include
DEPENDPATH += $$PWD/../3rd-party/qzxing3/include

windows {
# MinGW
-g++ {
QMAKE_LFLAGS_WINDOWS += -Wl,--stack,16777216
}
# MSVC
-msvc {
QMAKE_LFLAGS += /STACK:16777216
}
}

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:

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
Run CMake
Build the project. It should build successfully
Open the CMakeLists.txt file
Utilize this new, simple CMakeLists.txt file as a template for your ORIGINAL project.
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.
Modify the "template" CMakeLists.txt file to include the QT packages you are using (Core, Gui, or etc.)
Modify the "template" CMakeLists.txt file to include the target link libraries (refer to packages in previous step)
Build your original project
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
Resolve errors
Rebuild. It built successfully for me.