NAME¶

std::vector::clear - std::vector::clear

Synopsis¶

void clear(); (until C++11)
void clear() noexcept; (since C++11)
(until C++20)
constexpr void clear() noexcept; (since C++20)

Erases all elements from the container. After this call, size() returns zero.

Invalidates any references, pointers, or iterators referring to contained elements.
Any past-the-end iterators are also invalidated.

Leaves the capacity() of the vector unchanged (note: the standard's restriction on
the changes to capacity is in the specification of vector::reserve, see [1])

Parameters¶

(none)

Return value¶

(none)

Complexity¶

Linear in the size of the container, i.e., the number of elements.

Example¶

// Run this code

#include <algorithm>
#include <iostream>
#include <vector>

int main()
{
std::vector<int> container{1, 2, 3};

auto print = [](const int& n) { std::cout << " " << n; };

std::cout << "Before clear:";
std::for_each(container.begin(), container.end(), print);
std::cout << "\nSize=" << container.size() << ", Capacity=" << container.capacity() << '\n';

std::cout << "Clear\n";
container.clear();

std::cout << "After clear:";
std::for_each(container.begin(), container.end(), print);
std::cout << "\nSize=" << container.size() << ", Capacity=" << container.capacity() << '\n';
}

Output:¶

Before clear: 1 2 3
Size=3, Capacity=3
Clear
After clear:
Size=0, Capacity=3

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 2231 C++11 complexity guarantee was mistakenly complexity reaffirmed as
omitted in C++11 linear

See also¶

erase erases elements
(public member function)