What does this kind of C++ class declaration mean?

Question

I downloaded Ogre3D source code, and found this kind of class declaration:

class _OgreExport TimeIndex
{ ...

I know \"TimeIndex\" is the class

Answer 1

_OgreExport is a preprocessor directive that expands to either

__declspec(dllimport)

when the file is included outside its module or

__declspec(dllexport)

otherwise. Under Windows, you have to specify which classes/methods you want exported/imported so that they can be used across binaries.

Technically, as James pointed out in the comments, the macro name is illegal, since it begins with an underscore. These names are reserved for the implementation.