how to fix linker error in eclipse on linux

micha_eleric

using eclipse on linux
error, i am mostly sure is an eclipse issue, and not a programming issue.

g++ -L/usr/include/qt4 -L/usr/include/qt4/QtSerialPort -L/usr/include/qt4/QtGui -o "GUI2" ./src/CGUI.o ./src/Main.o
/usr/bin/ld: ./src/CGUI.o: in function CGUI::CGUI()': /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference toQMainWindow::QMainWindow(QWidget*, QFlagsQt::WindowType)'
/usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference to vtable for CGUI' /usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference tovtable for CGUI'
/usr/bin/ld: ./src/CGUI.o: in function CGUI::~CGUI()': /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:15: undefined reference tovtable for CGUI'
/usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:15: undefined reference to vtable for CGUI' /usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:15: undefined reference toQMainWindow::~QMainWindow()'
/usr/bin/ld: ./src/Main.o: in function main': /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/Main.cpp:14: undefined reference toQApplication::QApplication(int&, char**, int)'
/usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/Main.cpp:17: undefined reference to QApplication::exec()' /usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/Main.cpp:14: undefined reference toQApplication::~QApplication()'
/usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/Main.cpp:14: undefined reference to `QApplication::~QApplication()'
collect2: error: ld returned 1 exit status
make: *** [makefile:47: GUI2] Error 1

based on https://forum.qt.io/topic/101400/qt-with-eclipse-c/5 , i added QtCore and QtWidgets, even though there were no errors with #include<>. same errors from compile.

https://stackoverflow.com/questions/6478317/eclipse-undefined-reference says it is a linker error

under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->command: g++

under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Libraries->Libraries (-l) [nothing]

under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Libraries->Libraries search path (-L) /usr/include/qt4 /usr/include/qt4/QtWidgets /usr/include/qt4/QtCore /usr/include/qt4/QtSerialPort /usr/include/qt4/QtGui

under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Miscellaneous->Linker flags [nothing]

under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Miscellaneous->Other options (-Xlinker [option]) [nothing]

under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Miscellaneous->Other objects [nothing]

under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Shared Library Settings [nothing][nothing][nothing][nothing]

what is suppose to be added, and where?

if:
under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Libraries->Libraries (-l) /usr/include/qt4/QtGui
error:
/usr/bin/ld: cannot find -l/usr/include/qt4/QtGui

if:
under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Miscellaneous->Other options (-Xlinker [option]) /usr/include/qt4/QtGui
error:
/usr/bin/ld: cannot find /usr/include/qt4/QtGui: file format not recognized

if:
under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Miscellaneous->Other objects /usr/include/qt4/QtGui
error:
/usr/bin/ld: cannot find /usr/include/qt4/QtGui: file format not recognized

if it is a virtual function that has to be defined, then what would it be, other than constructor/destructor?

micha_eleric

@jsulm only "hacking" i am doing, is trying to find the path to the lib

jsulm

@micha_eleric said in how to fix linker error in eclipse on linux:

under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Libraries->Libraries search path (-L) /usr/include/qt4 /usr/include/qt4/QtWidgets

You are again adding include folder as library folder, why?! I already told you before that you need to set folder containing the libraries and we even figured out what it is (/lib/x86_64-linux-gnu). So, please set proper library folder...

micha_eleric

@jsulm

"there are no .h files for QMainWindow under Qt5 anywhere" - of course there is if you installed qtwidgets module, see https://doc.qt.io/qt-5/qmainwindow.html

not an install link

jsulm

@micha_eleric said in how to fix linker error in eclipse on linux:

not an install link

I don't know what this means...
If you installed Qt5 properly there will be QMainWindow header file.
This thread is already 36 posts long. Maybe you should do what was suggested? Like setting proper lib folder?

micha_eleric

@jsulm said in how to fix linker error in eclipse on linux:

@micha_eleric said in how to fix linker error in eclipse on linux:

not an install link

I don't know what this means...
If you installed Qt5 properly there will be QMainWindow header file.
This thread is already 36 posts long. Maybe you should do what was suggested? Like setting proper lib folder?

set proper lib folder is what i have been trying

jsulm

@micha_eleric said in how to fix linker error in eclipse on linux:

set proper lib folder is what i have been trying

But why are you still setting wrong folder?
I repeat it once more: /lib/x86_64-linux-gnu should be the correct one not /usr/include/qt4 /usr/include/qt4/QtWidgets...

micha_eleric

@jsulm said in how to fix linker error in eclipse on linux:

@micha_eleric said in how to fix linker error in eclipse on linux:

set proper lib folder is what i have been trying

But why are you still setting wrong folder?
I repeat it once more: /lib/x86_64-linux-gnu should be the correct one not /usr/include/qt4 /usr/include/qt4/QtWidgets...

because it is the only dir that has .h files

micha_eleric

g++ -L/usr/lib/x86_64-linux-gnu -o "GUI2" ./src/CGUI.o ./src/Main.o

/usr/bin/ld: ./src/CGUI.o: in function `CGUI::CGUI(QWidget*)':

/home/michaeleric/eclipse-workspace/GUI2/Debug/../src
/CGUI.cpp:10: undefined reference to QMainWindow::QMainWindow(QWidget*, QFlags<Qt::WindowType>)' /usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference to vtable for CGUI'

jsulm

@micha_eleric said in how to fix linker error in eclipse on linux:

because it is the only dir that has .h files

Are you joking?
We are talking about folder containing LIBRARIES, not headers!
This tells you clearly that it is about libraries:
"under Properties->C/C++ Build->Settings->Tool Settings->GCC C++ Linker->Libraries->Libraries search path"

Could you please be so kind and set /lib/x86_64-linux-gnu there? Else I give up on this thread...

micha_eleric

g++ -L/usr/lib/x86_64-linux-gnu -L/usr/lib/x86_64-linux-gnu/qt5 -L/usr/lib/qt5 -o "GUI2" ./src/CGUI.o ./src/Main.o

still gives same errors

micha_eleric

g++ -L/usr/lib/x86_64-linux-gnu -L/usr -L/ -L/usr/lib -L/usr/lib/x86_64-linux-gnu/qt5 -L/usr/lib/qt5 -o "GUI2" ./src/CGUI.o ./src/Main.o

gives same errors

i keep wandering if i properly installed qt, keep rechecking sudo install qt, and keep coming back to sites i already went to.

jsulm

@micha_eleric -L is not enough. You also have to tell the linker which libraries exactly you want to link.
This is done using -l parameter followed (without space) by the name of the library but without lib prefix and without .so extension.
Like:

-lQt5Gui

micha_eleric

@jsulm i cant find any qmainwindow, mainwindow, anything close to mainwindow in /usr/lib/x86_64-linux-gnu/
the only place anything close to mainwindow are .h files under qt4

wandering if qt4 .h files is the issue

micha_eleric

g++ -L/usr/lib/x86_64-linux-gnu -L/usr -L/ -L/usr/lib -L/usr/lib/x86_64-linux-gnu/qt5 -L/usr/lib/qt5 -o "GUI2" ./src/CGUI.o ./src/Main.o /usr/lib/x86_64-linux-gnu/libQtGui.so
/usr/bin/ld: ./src/CGUI.o: in function CGUI::CGUI(QWidget*)': /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference to vtable for CGUI'
/usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference to vtable for CGUI' /usr/bin/ld: ./src/CGUI.o: in function CGUI::~CGUI()':
/home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:15: undefined reference to vtable for CGUI' /usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:15: undefined reference to vtable for CGUI'

jsulm

@micha_eleric said in how to fix linker error in eclipse on linux:

i cant find any qmainwindow, mainwindow, anything close to mainwindow in /usr/lib/x86_64-linux-gnu/

Of course not. QMainWindow is part of widgets module as you can easilly see in the documentation: https://doc.qt.io/qt-5/qmainwindow.html (qmake: QT += widgets)
That means you should look for libQt5Widgets.so in /usr/lib/x86_64-linux-gnu.
And "surprisingly" it is there in your own list of libs: /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5

micha_eleric

@jsulm g++ -L/usr/lib/x86_64-linux-gnu -L/usr -L/ -L/usr/lib -L/usr/lib/x86_64-linux-gnu/qt5 -L/usr/lib/qt5 -o "GUI2" ./src/CGUI.o ./src/Main.o /usr/lib/x86_64-linux-gnu/libQtGui.so /usr/lib/x86_64-linux-gnu/libQt5Widgets.so
/usr/bin/ld: ./src/CGUI.o: in function CGUI::CGUI(QWidget*)': /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference to vtable for CGUI'
/usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference to vtable for CGUI' /usr/bin/ld: ./src/CGUI.o: in function CGUI::~CGUI()':
/home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:15: undefined reference to vtable for CGUI' /usr/bin/ld: /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:15: undefined reference to vtable for CGUI'

jsulm

@micha_eleric said in how to fix linker error in eclipse on linux:

/usr/bin/ld: ./src/CGUI.o: in function CGUI::CGUI(QWidget*)': /home/michaeleric/eclipse-workspace/GUI2/Debug/../src/CGUI.cpp:10: undefined reference tovtable for CGUI'

This is now another problem.
Classes which subclass QObject need moc tool (see https://doc.qt.io/qt-5/moc.html for more details). You can of course do that manually somehow.
But I would strongly recommend to use a proper build tool, either qmake or CMake. Both will call moc for your.

micha_eleric

@jsulm thank you

micha_eleric

@jsulm

This is now another problem.
Classes which subclass QObject need moc tool (see https://doc.qt.io/qt-5/moc.html for more details). You can of course do that manually somehow.
But I would strongly recommend to use a proper build tool, either qmake or CMake. Both will call moc for your.

and not part of the install