how to fix linker error in eclipse on linux

[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

[jsulm]

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

and not part of the install

Do you mean moc? If you properly installed Qt development packages then it should be there.
On my Ubuntu: /usr/bin/moc

[micha_eleric]

@jsulm using eclipse

[micha_eleric]

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

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

[JonB]

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

@JonB for me, find /usr/lib -name'*Qt5 *', anr find /usr/lib -name *Qt5 * had same results. [note] no space between 5 and *

Not if you did as I carefully stated and had any file with Qt5 in its name in the directory where you were when you typed in that find command, as I explained.....
@JonB said in how to fix linker error in eclipse on linux:

P.S.
If anyone does not believe me: before running the command do a touch Qt5 in the directory you run find /usr/lib -name '*Qt5*' versus find /usr/lib -name *Qt5* from., and compare the results...

Did you do that touch or not?

[micha_eleric]

@JonB touch did something different, but not touch *Qt5 *, and touch '*Qt5 *'