std::vector (3) - Linux Manuals

std::vector: std::vector

NAME

std::vector - std::vector

Synopsis

Defined in header <vector>
template<
class T, (1)
class Allocator = std::allocator<T>
> class vector;
namespace pmr {
template <class T> (2) (since C++17)
using vector = std::vector<T, std::pmr::polymorphic_allocator<T>>;
}

1) std::vector is a sequence container that encapsulates dynamic size arrays.
2) std::pmr::vector is an alias template that uses a polymorphic_allocator

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. (since C++03)

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. 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, SequenceContainer
, ContiguousContainer
(since C++17) and ReversibleContainer.

Template parameters

            The type of the elements.

            T must meet the requirements of CopyAssignable and CopyConstructible. (until C++11)
T - The requirements that are imposed on the elements depend on the actual operations performed on the container. Generally, it is required that element type is a complete type and meets the requirements of Erasable, but many member functions impose stricter requirements. (since C++11)
                                                                                                                                                                                                                                                                                                                                                                                                                               (until C++17)
            The requirements that are imposed on the elements depend on the actual operations performed on the container. Generally, it is required that element type meets the requirements of Erasable, but many member functions impose stricter requirements. This container (but not its members) can be instantiated with an incomplete element type if the allocator satisfies the allocator_completeness_requirements. (since C++17)

Allocator - An allocator that is used to acquire/release memory and to construct/destroy the elements in that memory. The type must meet the requirements of Allocator. The behavior is undefined if Allocator::value_type is not the same as T.

Specializations

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

             space-efficient dynamic bitset
vector<bool> (class template specialization)

Iterator invalidation

 This section is incomplete

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

Operations Invalidated
All read only operations, swap, std::swap Never
clear, operator=, assign Always
reserve, shrink_to_fit If the vector changed capacity, all of them. If not, none.
erase Erased elements + all elements after them (including end())
push_back, emplace_back If the vector changed capacity, all of them. If not, only end().
insert, emplace, resize If the vector changed capacity, all of them. If not, only those after the insertion point.
pop_back The element erased and end().

Member types

Member type Definition
value_type T
allocator_type Allocator
size_type Unsigned integer type (usually std::size_t)
difference_type Signed integer type (usually std::ptrdiff_t)

reference Allocator::reference (until C++11)
                       value_type& (since C++11)

const_reference Allocator::const_reference (until C++11)
                       const value_type& (since C++11)

pointer Allocator::pointer (until C++11)
                       std::allocator_traits<Allocator>::pointer (since C++11)

const_pointer Allocator::const_pointer (until C++11)
                       std::allocator_traits<Allocator>::const_pointer (since C++11)

iterator LegacyRandomAccessIterator
const_iterator Constant LegacyRandomAccessIterator
reverse_iterator std::reverse_iterator<iterator>
const_reverse_iterator std::reverse_iterator<const_iterator>

Member functions

              constructs the vector
constructor (public member function)
              destructs the vector
destructor (public member function)
              assigns values to the container
operator= (public member function)
              assigns values to the container
assign (public member function)
              returns the associated allocator
get_allocator (public member function)

Element access

              access specified element with bounds checking
at (public member function)
              access specified element
operator[] (public member function)
              access the first element
front (public member function)
              access the last element
back (public member function)

data direct access to the underlying array
              (public member function)
(C++11)

Iterators

begin returns an iterator to the beginning
cbegin (public member function)

end_ returns an iterator to the end
cend (public member function)

rbegin returns a reverse iterator to the beginning
crbegin (public member function)

rend returns a reverse iterator to the end
crend (public member function)

Capacity

              checks whether the container is empty
empty (public member function)
              returns the number of elements
size (public member function)
              returns the maximum possible number of elements
max_size (public member function)
              reserves storage
reserve (public member function)
              returns the number of elements that can be held in currently allocated storage
capacity (public member function)

shrink_to_fit reduces memory usage by freeing unused memory
              (public member function)
(C++11)

Modifiers

              clears the contents
clear (public member function)
              inserts elements
insert (public member function)

emplace constructs element in-place
              (public member function)
(C++11)
              erases elements
erase (public member function)
              adds an element to the end
push_back (public member function)

emplace_back constructs an element in-place at the end
              (public member function)
(C++11)
              removes the last element
pop_back (public member function)
              changes the number of elements stored
resize (public member function)
              swaps the contents
swap (public member function)

Non-member functions

operator==
operator!= lexicographically compares the values in the vector
operator< (function template)
operator<=
operator>
operator>=
                       specializes the std::swap algorithm
std::swap(std::vector) (function template)

erase(std::vector) Erases all elements satisfying specific criteria
erase_if(std::vector) (function template)

(C++20)

Deduction_guides(since C++17)

Example

// Run this code

  #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';
      }
  }

Output:

  7
  5
  16
  8
  25
  13