Template parameters T Type of the elements. Allocator-aware The container uses an allocator object to dynamically handle its storage needs. Dynamic array Allows direct access to any element in the sequence, even through pointer arithmetics, and provides relatively fast addition/removal of elements at the end of the sequence. Individual elements are accessed by their position in this sequence. For operations that involve inserting or removing elements at positions other than the end, they perform worse than the others, and have less consistent iterators and references than lists and forward_lists.Ĭontainer properties Sequence Elements in sequence containers are ordered in a strict linear sequence. Therefore, compared to arrays, vectors consume more memory in exchange for the ability to manage storage and grow dynamically in an efficient way.Ĭompared to the other dynamic sequence containers ( deques, lists and forward_lists), vectors are very efficient accessing its elements (just like arrays) and relatively efficient adding or removing elements from its end. Libraries can implement different strategies for growth to balance between memory usage and reallocations, but in any case, reallocations should only happen at logarithmically growing intervals of size so that the insertion of individual elements at the end of the vector can be provided with amortized constant time complexity (see push_back). Instead, vector containers may allocate some extra storage to accommodate for possible growth, and thus the container may have an actual capacity greater than the storage strictly needed to contain its elements (i.e., its size). This is a relatively expensive task in terms of processing time, and thus, vectors do not reallocate each time an element is added to the container. This array may need to be reallocated in order to grow in size when new elements are inserted, which implies allocating a new array and moving all elements to it.
Internally, vectors use a dynamically allocated array to store their elements. But unlike arrays, their size can change dynamically, with their storage being handled automatically by the container. Just like arrays, vectors use contiguous storage locations for their elements, which means that their elements can also be accessed using offsets on regular pointers to its elements, and just as efficiently as in arrays. Vectors are sequence containers representing arrays that can change in size.
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