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std::vector capacity() method

// prism-push-types:size_type
// Const version only
constexpr size_type capacity() const noexcept;

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 - O(1).

Example

Main.cpp
#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';
}
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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.

std::vector capacity() method

// prism-push-types:size_type
// Const version only
constexpr size_type capacity() const noexcept;

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 - O(1).

Example

Main.cpp
#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';
}
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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.