inline vs __inline vs __inline__ vs __forceinline?

Question

What are the differences between these four inline (key)words?

inline, __inline, __inline__, __forceinline.

Answer 1

__inline, __inline__ and __forceinline are all implementation specific. Because of the double underscore they are all identifiers reserved for the implementation so shouldn't conflict with identifiers used in applications.

inline is the only C++ keyword.