Why would I prefer using vector to deque

Since:

1. (I presume) they are both contiguous memory containers;
2. feature wise, deque has almost everything vector has but more, since it is more efficient to insert in the front.

Why would anyone prefer std::vector to std::deque?

Elements in a deque are not contiguous in memory; vector elements are guaranteed to be. So if you need to interact with a plain C library that needs contiguous arrays, or if you care (a lot) about spatial locality, then you might prefer vector. In addition, since there is some extra bookkeeping, other ops are probably (slightly) more expensive than their equivalent vector operations. On the other hand, using many/large instances of vector may lead to unnecessary heap fragmentation (slowing down calls to new).

Also, as pointed out elsewhere on StackOverflow, there is more good discussion here: http://www.gotw.ca/gotw/054.htm .