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

 

C++

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Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

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forward_list (C++11)

list

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unordered_set (C++11)

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unordered_map (C++11)

unordered_multimap (C++11)

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stack

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span (C++20)

 

std::vector

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vector::vector

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vector::assign

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Element access

vector::at

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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

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vector::reserve

vector::capacity

vector::shrink_to_fit (C++11)

Modifiers

vector::clear

vector::insert

vector::emplace (C++11)

vector::erase

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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)

 

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 omitted in C++11	complexity reaffirmed as linear

See also

erase

erases elements (public member function)