Which statement describes an intrusive linked list?

• A. Intrusive lists store the next pointer inside the stored data.
• B. Intrusive lists require a separate wrapper for each element.
• C. Intrusive lists cannot be used in embedded systems.
• D. Intrusive lists are identical to non-intrusive lists.

Answer: (A)

Intrusive linked lists embed their bookkeeping inside the elements themselves. The next (and sometimes previous) pointer is a field that lives inside the data object being stored, so there isn’t a separate node wrapper around each element. This means the data type must be designed to participate in the list, and you get lower memory overhead and faster operations since there’s no extra allocation or indirection for a separate node.

That’s why the statement about storing the next pointer inside the stored data is the best description. The other ideas describe non-intrusive lists (which use separate wrappers), claim limitations that aren’t inherent to intrusive lists (such as being unsuitable for embedded systems), or say they’re identical to non-intrusive lists, which they are not.