Your files have #include "serialport.h", like the rest of the dosbox project. Your code is referring to your custom header file ..\src\serialport.h - the rest of the dosbox code still requires the include\serialport.h header. This is causing some compiler confusion.
I'd like to rename your file to something like src\serialport2.h (?), but I haven't been able to determine how many source files are looking for your version as opposed to the original header.
Could you offer some pointers as to which of your files need to be modified?
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