What does this line (modifier in the macro) mean?

Question

C++ / C#

Hello! Please explain how such a MYLIBAPI modifier will affect the functions?
#define MYLIBAPI extern "С" __declspec(dllimport)

Answer 1

The macro simplifies the import from the dll into the program. Wherever you use "MYLIBAPI", the dll import directive will expand.
extern "C" means to use simple function signature generation (C style) when getting object files. In particular, it prevents the C++ compiler from "decorating" (or "beautifying") a function name with additional characters when working with a DLL
Example:
extern "C" __declspec(dllimport)double AddNumbers(double a, double b);
in your case, you can write
MYLIBAPI double AddNumbers(double a, double b);

Answer 2

It's not a modifier. This is the name of the macro. And then there is his body. Now everywhere in the code MYLIBAPI will be replaced by the body.