error gui at debian9 (QXcbConnection: Could not connect to display)

[VLeshka]

Hi!

I have compile the gui program by QT5.9 (sudo apt install qt5-default).

The compiling complete finely at lxqt and debian9:

sudo apt install qt5-default

cd program_directory

make clean

make

At lxqt, the binary program runs finely. But lxqt take up too much space, so I need in debian9.

But at debian9, running the binary file returns an error:

QXcbConnection: Could not connect to display

I have made:

export DISPLAY=:0.0

sudo apt install libffi-dev phantomjs gksu xserver-xorg

But the error is still present.

Also I can run the gui program at debian9 from another PC by:

ssh -X 192.168.X.X -l debian

but this doesn't solve the problem.

P.S.

I was advised here, and then my topic was deleted:

You are going to have to add enough stuff to provide, at minimum, an X
server implementation -- and most likely you'll need a window/desktop
manager.

The xserver is installed.

Please help.