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!