std::vector

template<
    class T,
    class Allocator = std::allocator<T>
> class vector;

namespace pmr {
    template <class T>
    using vector = std::vector<T, std::polymorphic_allocator<T>>;
}

The storage of the vector is handled automatically, being expanded and contracted as needed. Vectors usually occupy more space than static arrays, because more memory is allocated to handle future growth. This way a vector does not need to reallocate each time an element is inserted, but only when the additional memory is exhausted. The total amount of allocated memory can be queried using capacity() function. Extra memory can be returned to the system via a call to shrink_to_fit(). (since C++11).

Reallocations are usually costly operations in terms of performance. reserve() function can be used to eliminate reallocations if the number of elements is known beforehand.

The complexity (efficiency) of common operations on vectors is as follows:

• Random access - constant O(1)
• Insertion or removal of elements at the end - amortized constant O(1)
• Insertion or removal of elements - linear in distance to the end of the vector O(n)

std::vector meets the requirements of Container, AllocatorAwareContainer, SequenceContainer , ContiguousContainer (for T other than bool) (since C++17) and ReversibleContainer.

Template parameters

Specializations

The standard library provides a specialization of std::vector for the type bool, which is optimized for space efficiency.

Iterator invalidation

There are still a few inaccuracies in this section. Refer to individual member function pages for more detail.

Member types

Member functions

Non-member functions

Example

#include <iostream>
#include <vector>
 
int main()
{
    // Create a vector containing integers
    std::vector<int> v = {7, 5, 16, 8};
 
    // Add two more integers to vector
    v.push_back(25);
    v.push_back(13);
 
    // Iterate and print values of vector
    for(int n : v) {
        std::cout << n << '\n';
    }
}

7
5
16
8
25
13