NAME¶

std::vector::capacity - std::vector::capacity

Synopsis¶

size_type capacity() const; (noexcept since C++11)
(constexpr 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 <iomanip>
#include <iostream>
#include <vector>

int main()
{
int sz = 100;
std::vector<int> v;

auto cap = v.capacity();
std::cout << "Initial size: " << v.size() << ", capacity: " << cap << '\n';

std::cout << "\nDemonstrate the capacity's growth policy."
"\nSize: Capacity: Ratio:\n" << std::left;
while (sz-- > 0)
{
v.push_back(sz);
if (cap != v.capacity())
{
std::cout << std::setw( 7) << v.size()
<< std::setw(11) << v.capacity()
<< std::setw(10) << v.capacity() / static_cast<float>(cap) << '\n';
cap = v.capacity();
}
}

std::cout << "\nFinal size: " << v.size() << ", capacity: " << v.capacity() << '\n';
}

Possible output:¶

Initial size: 0, capacity: 0

Demonstrate the capacity's growth policy.
Size: Capacity: Ratio:
1 1 inf
2 2 2
3 4 2
5 8 2
9 16 2
17 32 2
33 64 2
65 128 2

Final size: 100, capacity: 128

See also¶

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