Why would I prefer using vector to deque

Question

Since

1. they are both contiguous memory containers;
2. feature wise, deque has almost everything vector has but more, since it is more efficient to insert

Answer 1

According to http://www.cplusplus.com/reference/stl/deque/, "unlike vectors, deques are not guaranteed to have all its elements in contiguous storage locations, eliminating thus the possibility of safe access through pointer arithmetics."

Deques are a bit more complicated, in part because they don't necessarily have a contiguous memory layout. If you need that feature, you should not use a deque.

(Previously, my answer brought up a lack of standardization (from the same source as above, "deques may be implemented by specific libraries in different ways"), but that actually applies to just about any standard library data type.)