Undefined Reference to hal_export_funct Linker Error in LinuxCNC HAL Component

The reason I am using Qt C++ is that the existing external module, which was developed in C++, is incompatible with Qt Python (QtPy).

Thanks.

LINUXCNC_HOME then, what is its value?

A bit left field but how did you install linuxcnc? If installed on Trixie and not the LinuxCNC ISO, did you
sudo apt install linuxcnc-uspace-dev
I think this is needed to get the required libs (certainly for halcompile)
The ISO installs linuxcnc-uspace-dev

LINUXCNC_HOME : /home/user1/linuxcnc

The Qt application now works correctly when I comment out the following two lines in the build configuration:

- LIBS += -L/home/user1/linuxcnc/rtlib -lhal_lib

- hal_export_funct.

Thanks

I built LinuxCNC from source on Ubuntu.

Thanks.

Look at the exact line that is executed to link the application.
You should be able to see the exact command with all values that are actually used.
Troubleshoot that line first. If that's wrong, fix the makefile.