std::vector<T,Allocator>::capacity

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Containers library

array (C++11)

vector

deque

forward_list (C++11)

list

set

multiset

map

multimap

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

stack

queue

priority_queue

span (C++20)

 

std::vector

Member functions

vector::vector

vector::~vector

vector::operator=

vector::assign

vector::get_allocator

Element access

vector::at

vector::operator[]

vector::front

vector::back

vector::data (C++11)

Iterators

vector::beginvector::cbegin (C++11)

vector::endvector::cend (C++11)

vector::rbeginvector::crbegin (C++11)

vector::rendvector::crend (C++11)

Capacity

vector::empty

vector::size

vector::max_size

vector::reserve

vector::capacity

vector::shrink_to_fit (C++11)

Modifiers

vector::clear

vector::insert

vector::emplace (C++11)

vector::erase

vector::push_back

vector::emplace_back (C++11)

vector::pop_back

vector::resize

vector::swap

Non-member functions

std::swap

eraseerase_if (C++20)(C++20)

operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

Deduction guides(C++17)

 

size_type capacity() const;		(until C++11)
size_type capacity() const noexcept;		(since C++11) (until C++20)
constexpr size_type capacity() const noexcept;		(since C++20)

Returns the number of elements that the container has currently allocated space for.

Parameters

(none)

Return value

Capacity of the currently allocated storage.

Complexity

Constant.

Example

Run this code

#include <iostream>
#include <vector>
 
int main()
{
    int sz = 200;
    std::vector<int> v1;
 
    auto cap = v1.capacity();
    std::cout << "initial capacity=" << cap << '\n';
 
    for (int n = 0; n < sz; ++n) {
        v1.push_back(n);
        if (cap != v1.capacity()) {
            cap = v1.capacity();
            std::cout << "new capacity=" << cap << '\n';
        }
    }
 
    std::cout << "final size=" << v1.size() << '\n';
    std::cout << "final capacity=" << v1.capacity() << '\n';
}

Possible output:

initial capacity=0
new capacity=1
new capacity=2
new capacity=4
new capacity=8
new capacity=16
new capacity=32
new capacity=64
new capacity=128
new capacity=256
final size=200
final capacity=256

See also

size	returns the number of elements (public member function)
reserve	reserves storage (public member function)