What defines an opaque type in C, and when are they necessary and/or useful?

Question

I\'ve seen the concept of \'opaque types\' thrown around a bit but I really haven\'t found a succinct answer as to what defines an opaque type in C and more importantly what

Answer 1

In my understanding, opaque types are those which allow you to hold a handle (i.e., a pointer) to an structure, but not modify or view its contents directly (if you are allowed to at all, you do so through helper functions which understand the internal structure).

Opaque types are, in part, a way to make C more object-oriented. They allow encapsulation, so that the internal details of a type can change--or be implemented differently in different platforms/situations--without the code that uses it having to change.