Thread: Dll Header

Code:

 #ifndef _DLL_H_
#define _DLL_H_

#if BUILDING_DLL
# define DLLIMPORT __declspec (dllexport)
#else /* Not BUILDING_DLL */
# define DLLIMPORT __declspec (dllimport)
#endif /* Not BUILDING_DLL */


DLLIMPORT void HelloWorld (void);


#endif /* _DLL_H_ */

Here is a standard devc++ header file for a dll.
What does BUILDING_DLL mean and if I change the name of the header file to loop.h should i change _DLL_H_?