Using dynamic library .dll to interface Arduino using COM port .

Some time ago I tryed to use a simple C winapi window to comunicate to Arduino using serial. I used information on https://playground.arduino.cc/Interfacing/CPlusPlus . The results was a .dll file that may be included in some project. I used VC6 to compile. Results in 3 files: dllCOM.dll, dllCOM.h and dllCOM.lib.

dllCOM.zip (47.1 KB)

This is the complete C project .

dllCOM.zip (57.9 KB)

what is the problem?
any particular reason to use VC6? why not Visual Studio Express 2017 which has the SerialPort component
an alternative is to use jSerialComm with Java

No, its my own preference, because it I used for a long time. By the way, if you could to modify to improve it I really apreciate.
The question is: it may be made better? In case of using newer compiler, like a VS 2017, how can we do it? Thank you.