When to use void* pointer

What is void* pointer in C++ ?
By standard it is a pointer to an object of unknown type ( of course, if not null).
"Unknown" means unknown for one type of users and known to the other type of users, particularly to the owner of this "unknown" type.
An example of usage of void* pointer is a proxy pointer to something which internal structure should be hidden, secret or invisible.

http://code.google.com/p/javahotel/wiki/UseVoidPointer#Top_secret_usage_of_void_pointer

"secretpointer" can point to anything but this way we get off C++ object oriented paradigm.

Another way is to split class declaration into two parts: public and private/hidden. Nothing new, one can say, all the time we can have public and private declarations in a class definition. But the disadvantage of the standard approach is that not only public but also private method and attributes should be exposed in a class declaration. Also every change in a private section involves recompiling the users of this classes. Below is an example of class splited into public and hidden part.

http://code.google.com/p/javahotel/wiki/UseVoidPointer#Partially_secret_class_definition