How to fix GCC error: expected constructor, destructor, or type conversion before __declspec(dllexport)

Problem:

When trying to compile an application on Linux, you see a compiler error message like

myheader.h:23:12: error: expected constructor, destructor, or type conversion before ‘(’ token
    23 |  __declspec(dllexport) int myfunc(

Solution

__declspec(dllexport) is a Windows-specific feature and not available on Linux. In order to fix it in a compatible way, add this code either in a header that is included in every file containing __declspec(dllexport) or add it in each file where the error occurs:

#ifdef __linux__
#define __declspec(v)
#endif

This will basically ignore any __declspec() call on the preprocessor level.