How start compiler in Ubuntu 20

JonB

@Mikeeeeee
You need to do just what @mrjj stated:

Open a console/terminal.
Type: export QT_DEBUG_PLUGINS=1
Type the path to the Qt Creator executable to run it.

Because it has been run from a shell with that environment variable exported, you will get debug output showing you where it's looking for what, to diagnose your problem.

Mikeeeeee

@JonB said in How start compiler in Ubuntu 20:

export QT_DEBUG_PLUGINS = 1

this

export QT_DEBUG_PLUGINS = 1

return errors:

bash: export: «=»: this is an invalid identifier
bash: export: «1»: this is an invalid identifier

JonB

@Mikeeeeee said in How start compiler in Ubuntu 20:
I just copied what @mrjj typed. Correct is to remove the spaces:

export QT_DEBUG_PLUGINS=1

If it had been me, I would have typed man bash and searched for export for myself:

export [-fn] [name[=word]] ...

Mikeeeeee

I write this in folder "Qt", but qt did not issue any new errors. Still, maybe this is because the installer might not have downloaded the files?

JonB

@Mikeeeeee
Prior to the qt.qpa.plugin: Could not load ... error message, because of the environment variable you should have output (in the terminal) on where it looked for plugin xcb but failed to find it.

Mikeeeeee

It doesn't issue any more errors.
I have only this build log:

/home/admin1/Qt/5.15.0/gcc_64/bin/uic ../test/mainwindow.ui -o ui_mainwindow.h
g++ -c -pipe -g -std=gnu++11 -Wall -Wextra -D_REENTRANT -fPIC -DQT_DEPRECATED_WARNINGS -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../test -I. -I../../Qt/5.15.0/gcc_64/include -I../../Qt/5.15.0/gcc_64/include/QtWidgets -I../../Qt/5.15.0/gcc_64/include/QtGui -I../../Qt/5.15.0/gcc_64/include/QtCore -I. -isystem /usr/include/libdrm -I. -I../../Qt/5.15.0/gcc_64/mkspecs/linux-g++ -o main.o ../test/main.cpp
g++ -pipe -g -std=gnu++11 -Wall -Wextra -dM -E -o moc_predefs.h ../../Qt/5.15.0/gcc_64/mkspecs/features/data/dummy.cpp
g++ -c -pipe -g -std=gnu++11 -Wall -Wextra -D_REENTRANT -fPIC -DQT_DEPRECATED_WARNINGS -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../test -I. -I../../Qt/5.15.0/gcc_64/include -I../../Qt/5.15.0/gcc_64/include/QtWidgets -I../../Qt/5.15.0/gcc_64/include/QtGui -I../../Qt/5.15.0/gcc_64/include/QtCore -I. -isystem /usr/include/libdrm -I. -I../../Qt/5.15.0/gcc_64/mkspecs/linux-g++ -o mainwindow.o ../test/mainwindow.cpp
/home/admin1/Qt/5.15.0/gcc_64/bin/moc -DQT_DEPRECATED_WARNINGS -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB --include /home/admin1/QtProjects/build-test-Desktop_Qt_5_15_0_GCC_64bit-Debug/moc_predefs.h -I/home/admin1/Qt/5.15.0/gcc_64/mkspecs/linux-g++ -I/home/admin1/QtProjects/test -I/home/admin1/Qt/5.15.0/gcc_64/include -I/home/admin1/Qt/5.15.0/gcc_64/include/QtWidgets -I/home/admin1/Qt/5.15.0/gcc_64/include/QtGui -I/home/admin1/Qt/5.15.0/gcc_64/include/QtCore -I. -I/usr/include/c++/9 -I/usr/include/x86_64-linux-gnu/c++/9 -I/usr/include/c++/9/backward -I/usr/lib/gcc/x86_64-linux-gnu/9/include -I/usr/local/include -I/usr/include/x86_64-linux-gnu -I/usr/include ../test/mainwindow.h -o moc_mainwindow.cpp
g++ -c -pipe -g -std=gnu++11 -Wall -Wextra -D_REENTRANT -fPIC -DQT_DEPRECATED_WARNINGS -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../test -I. -I../../Qt/5.15.0/gcc_64/include -I../../Qt/5.15.0/gcc_64/include/QtWidgets -I../../Qt/5.15.0/gcc_64/include/QtGui -I../../Qt/5.15.0/gcc_64/include/QtCore -I. -isystem /usr/include/libdrm -I. -I../../Qt/5.15.0/gcc_64/mkspecs/linux-g++ -o moc_mainwindow.o moc_mainwindow.cpp
g++ -Wl,-rpath,/home/admin1/Qt/5.15.0/gcc_64/lib -o test main.o mainwindow.o moc_mainwindow.o   /home/admin1/Qt/5.15.0/gcc_64/lib/libQt5Widgets.so /home/admin1/Qt/5.15.0/gcc_64/lib/libQt5Gui.so /home/admin1/Qt/5.15.0/gcc_64/lib/libQt5Core.so -lGL -lpthread

JonB

@Mikeeeeee
I don't understand. Your output now shows a compilation. I thought your problem as reported by you was when you tried to start an application:

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start ....

I have not seen you reproduce that error message with the environment variable switched on.

Mikeeeeee

This error persists. The error was always there and never changed.

SGaist

That's why we are asking you to start your application with the QT_DEBUG_PLUGINS environment variable set so that it provides more information at run time about what is happening to the xcb plugin.

Mikeeeeee

I started using QT_DEBUG_PLUGINS, but nothing has changed. QT_DEBUG_PLUGINS need to be registered in the "Qt" folder?

SGaist

How are you using exactly ?

Mikeeeeee

I write in folder "Qt" in console

export QT_DEBUG_PLUGINS=1

SGaist

The folder has no influence on that environment variable. And are you starting your application from the same terminal were you defined the variable ?

Mikeeeeee

I am restarted Qt.
Maybe I'm not there to change this variable. Explain in which folder I need to change this variable?

SGaist

As I already said: the folder has absolutely nothing to do with the environnement variable.

What do you mean by your restarted Qt ?

JonB

@Mikeeeeee
This really isn't very hard. You originally showed

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-

You ran a program to get this. I don't know whether it was Qt Creator or your own application, but it was one of them, whichever. Right?

As we have already told you:

Open a console/terminal.
Type: export QT_DEBUG_PLUGINS=1
Type the path to Qt Creator or your own executable to run it. Whichever one caused your original error.

At this point you should get your error again, but this time the environment variable should cause debug output, stating which it can't load "xcb".

Mikeeeeee

@JonBWhere and how do I specify the path to Qt Creator? Please provide a full example of using QT_DEBUG_PLUGINS.
And maybe the QT_DEBUG_PLUGINS plugin doesn't work either?

JonB

@Mikeeeeee
I have provided a full example. I have given you the exact steps. I would expect any developer to be able to follow them easily. I leave it to you.

Mikeeeeee

@JonB Please explain point 3. It is not clear how, where, or why to record the path.

jsulm

@Mikeeeeee Why is it so hard?! Do you know what a path is?
Just call QtCreator using full path to it, like:

/home/YOUR_USER_NAME/Qt/Tools/QtCreator/bin/qtcreator.sh

"And maybe the QT_DEBUG_PLUGINS plugin doesn't work either?" - QT_DEBUG_PLUGINS is not a plug-in! You already was told that it is an environment variable. I suggest you learn what an environment variable is (something a software developer should know).