What are the disadvantages of circular linked list over linear linked list?

Answer 1

This is not much of an answer but maybe helps to get started:

First, the assumption is that the question is indeed about circular vs linear lists, as opposed to uni-directional vs bi-directional lists.

A linear list is one that holds no valid, but in fact a designated invalid, value for the reference to the last item's successor, and the first item's predecessor. The name for this invalid reference value is subject to the implementation language, typically NULL, nil or nul.

A circular list only uses valid reference values. Two forms of rings exist: the closed ring and the sentinel ring.

The closed is one where the last item's successor references the first item, and the first item's predecessor refererences the last item.

A characteristic feature of closed rings is that the algorithm cannot normally stop iterating on an "end reached" criterion. There will be different criteria, subject to the algorithm. A closed ring can never be empty, but it can go in and out of existence.

A sentinel ring is one that contains one artificial element, the sentinel. This item acts as the anchor, as the last item's successor, and the first item's predecessor. A sentinel ring has the a well-defined start and stop (whenever iteration reaches the sentinel). The sentinel is an empty ring's only element. The reliable existence of the sentinel rids the ring of any invalid references; a useful aspect in the design of robust software.

I argue that there is no superiority of one of these data structures over the over in the general case. All have their place; superiority or inferiority of a data structure must always be rated in context with the algorithm and data in mind.