Function declarations using macros to support multiple platforms
Keep the DLLExport macro on all platforms, but make the definition resolve to nothing unless you're on Windows. You might also want to rename the macro to something more neutral. Something like this:

#if defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(_WIN64) || defined(WINAPI_FAMILY)
# define EXPORT __declspec(dllexport)
#else
# define EXPORT
#endif

extern "C"
{
EXPORT void initScreenPointPixel(void* buffer, int x, int y, int width, int height);
}


You should also be aware of that the extern "C" stuff is only recognized by a C++ compiler. The related statements should also be conditional, e.g.:

#ifdef __cplusplus
extern "C" {
#endif 

... declarations here

#ifdef __cplusplus
}
#endif