What “CV_EXPORTS_W” means

Question

Recently, I try to find out the source code of the \"calcOpticalFlowPyrLK\" function in OpenCV library. When I searched it\'s definition, I found a macro named \"CV_EXPORTS_

Answer 1

CV_EXPORTS_W is defined in modules/core/include/opencv2/core/types_c.h as an alias for CV_EXPORTS, and in the same file CV_EXPORTS is defined as:

#if (defined WIN32 || defined _WIN32 || defined WINCE) && defined CVAPI_EXPORTS
# define CV_EXPORTS __declspec(dllexport)
#else
# define CV_EXPORTS
#endif

In other words, it's an alias for __declspec(dllexport) on a windows platform where CVAPI_EXPORTS is defined, otherwise it's empty.