std::unordered_set<Key,Hash,KeyEqual,Allocator>::erase

 

C++

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Technical Specifications

 

Containers library

Sequence

array (C++11)

vector

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list

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multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

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stack

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span (C++20)

 

std::unordered_set

Member functions

unordered_set::unordered_set

unordered_set::~unordered_set

unordered_set::operator=

unordered_set::get_allocator

Iterators

unordered_set::beginunordered_set::cbegin

unordered_set::endunordered_set::cend

Capacity

unordered_set::empty

unordered_set::size

unordered_set::max_size

Modifiers

unordered_set::clear

unordered_set::insert

unordered_set::emplace

unordered_set::emplace_hint

unordered_set::erase

unordered_set::swap

unordered_set::extract (C++17)

unordered_set::merge (C++17)

Lookup

unordered_set::count

unordered_set::find

unordered_set::contains (C++20)

unordered_set::equal_range

Bucket interface

unordered_set::begin(size_type)unordered_set::cbegin(size_type)

unordered_set::end(size_type)unordered_set::cend(size_type)

unordered_set::bucket_count

unordered_set::max_bucket_count

unordered_set::bucket_size

unordered_set::bucket

Hash policy

unordered_set::load_factor

unordered_set::max_load_factor

unordered_set::rehash

unordered_set::reserve

Observers

unordered_set::hash_function

unordered_set::key_eq

Non-member functions

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

std::swap

erase_if (C++20)

Deduction guides(C++17)

 

	(1)
iterator erase( const_iterator pos );			(since C++11)
iterator erase( iterator pos );			(since C++17)
iterator erase( const_iterator first, const_iterator last );		(2)	(since C++11)
size_type erase( const key_type& key );		(3)	(since C++11)

Removes specified elements from the container.

1) Removes the element at pos.

2) Removes the elements in the range [first; last), which must be a valid range in *this.

3) Removes the element (if one exists) with the key equivalent to key.

References and iterators to the erased elements are invalidated. Other iterators and references are not invalidated.

The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos.

The order of the elements that are not erased is preserved. (This makes it possible to erase individual elements while iterating through the container.)

Parameters

pos	-	iterator to the element to remove
first, last	-	range of elements to remove
key	-	key value of the elements to remove

Return value

1-2) Iterator following the last removed element.

3) Number of elements removed (0 or 1).

Exceptions

1,2) Throws nothing.

3) Any exceptions thrown by the Compare object.

Complexity

Given an instance c of unordered_set:

1) Average case: constant, worst case: c.size()

2) Average case: std::distance(first, last), worst case: c.size()

3) Average case: c.count(key), worst case: c.size()

Example

Run this code

#include <unordered_set>
#include <iostream>
int main()
{
    std::unordered_set<int> c = {1, 2, 3, 4, 5, 6, 7, 8, 9};
 
    // erase all odd numbers from c
    for(auto it = c.begin(); it != c.end(); ) {
        if(*it % 2 != 0)
            it = c.erase(it);
        else
            ++it;
    }
 
    for(int n : c) {
        std::cout << n << ' ';
    }
}

Possible output:

2 4 6 8

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 2356	C++11	the order of element that are not erased was unspecified	required to be preserved

See also

clear (C++11)

clears the contents (public member function)