std::vector

Except for the std::vector<bool> partial specialization, 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. 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 storage of the vector is handled automatically, being expanded 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()^[1].

Reallocations are usually costly operations in terms of performance. The 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 the distance to the end of the vector 𝓞(n).

std::vector (for T other than bool) meets the requirements of Container, AllocatorAwareContainer(since C++11), SequenceContainer, ContiguousContainer(since C++17) and ReversibleContainer.

1. ↑ In libstdc++, shrink_to_fit() is not available in C++98 mode.

Template parameters

Specializations

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

Iterator invalidation

Member types

Member functions

Non-member functions

Notes

Example

#include <iostream>
#include <vector>
 
int main()
{
    // Create a vector containing integers
    std::vector<int> v = {8, 4, 5, 9};
 
    // Add two more integers to vector
    v.push_back(6);
    v.push_back(9);
 
    // Overwrite element at position 2
    v[2] = -1;
 
    // Print out the vector
    for (int n : v)
        std::cout << n << ' ';
    std::cout << '\n';
}

8 4 -1 9 6 9

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also