Hi Zhen,
[quote user="Zhen Li"]I did some research from website, I did not get clear answer for it.[/quote]
It's written in CONNECT Edition SDK readme and I remember it was discussed several times in this forum and also in BDN workshop and sessions: Visual Studio 2013 is required and particulary Professional Edition is supported by Bentley.
[quote user="Zhen Li"]Visual Studio 2015 professional will work for the Connect C++ MDL, right?[/quote]
No, it's bad assumption. It's not possible to mix different versions of C++ compiler used for dll/lib files and a code that will link these libraries. So if MicroStation CONNECT Edition is built using VS2013, you have to use VS2013 too.
I guess if you will compile your native C++ code using VS2015, it will be probably loaded, but memory access and allocation crashes will happen or other hard to debug problems will appear. I recommend to search internet for "dll version hell" topic, there are also plenty of articles on Microsoft MSDN website available.
If talking about CRT (C runtime), Visual Studio 2015 is very specific, because deep changes were implemented and a concept of Universal CRT that promises to make dll versions linking less confusing, but because of this it's quite different from VS2013 CRT and less compatible.
With regards,
Jan