How start compiler in Ubuntu 20

[SGaist]

Hi,

Set QT_DEBUG_PLUGINS environment variable to 1 and restart your application. You shall have more information about why it fails to load.

[Mikeeeeee]

@SGaist said in How start compiler in Ubuntu 20:

QT_DEBUG_PLUGINS

I write in .pro file:

QT_DEBUG_PLUGINS = 1

But the debag didn't record anything else.

[mrjj]

@Mikeeeeee
Hi
You must do that in a shell.
Not in the .pro file

So open a shell
type
export QT_DEBUG_PLUGINS = 1
and then start creator in this shell.

If you dont know where creator is, you can right click its icon and edit it and see path there.

[Mikeeeeee]

I don't understand you. Do I need to register this in the console?

[JonB]

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

1. Open a console/terminal.
2. Type: export QT_DEBUG_PLUGINS=1
3. 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:

1. Open a console/terminal.
2. Type: export QT_DEBUG_PLUGINS=1
3. 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".