Class Template Stack<T>’s Data Representation

Section 15.7.1 showed that the Standard Library’s stack adapter class can use various containers to store its elements. Of course, a stack requires insertions and deletions only at its top. So, for example, a vector or a deque could be used to store the stack’s elements. A vector supports fast insertions and deletions at its back. A deque supports fast insertions and deletions at its front and its back. A deque is the default representation for the Standard Library’s stack adapter because a deque grows more efficiently than a vector. A vector is maintained as a contiguous block of memory—when that block is full and a new element is added, the vector allocates a larger contiguous block of memory and copies the old elements into that new block. A deque, on the other hand, is typically implemented as list of fixed-size, built-in arrays—new fixed-size built-in arrays are added as necessary and none of the existing elements are copied when new items are added to the front or back. For these reasons, we use a deque (line 42) as the underlying container for our Stack class.