Member functions of std::vector are constexpr: it is possible to create and use std::vector objects in the evaluation of a constant expression. Std::vector (for T other than bool) meets the requirements of Container, AllocatorAwareContainer, SequenceContainer, ContiguousContainer (since C++17) and ReversibleContainer. Insertion or removal of elements - linear in the distance to the end of the vector O(n).Insertion or removal of elements at the end - amortized constant O(1).The complexity (efficiency) of common operations on vectors is as follows: The reserve() function can be used to eliminate reallocations if the number of elements is known beforehand. Reallocations are usually costly operations in terms of performance. Extra memory can be returned to the system via a call to shrink_to_fit().
The total amount of allocated memory can be queried using capacity() function. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. The storage of the vector is handled automatically, being expanded as needed. This means that a pointer to an element of a vector may be passed to any function that expects a pointer to an element of an array.
The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets to regular pointers to elements. 2) std::pmr::vector is an alias template that uses a polymorphic allocator.
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