If I'm clear on the question, you could checkout the 'BACnet Stack' project source code or even the 'VTS' source code too - for a C/C++ (language) reference.
Otherwise YABE is a good project in C# (language), but there's also a BACnet NuGet package available for C# too - along with the mechanics that underpin the YABE tool.
Sorry to my bad english.
So i use a automate with MERVIS software and i use a Bacnet server to have my variable in my IHM (weintek panel pc with Easybuilder Pro).
So all i make is good and work but i'm not happy to EasyBuilder pro and i want make my own HMI. I decide to make my application with QT in C++.
But i'm physicien at the begining so learn little bit by little bit( i have base of python,c++, structur text). I know nothing about how build a bacnet client and do you have idea where can i find some simple exemple to communicate with my PLC because i find nothing and i need to learn and make this to my project.
So i have my PLC, link in ethernet to my PC where i make my hmi. In the future i want put this application in PANEL PC tactil work in window and link to my PLC with MERVIS software.
Create Bacnet client variable automate