std::unordered_set erase() method
- since C++23
- since C++11
// (1) Non const version only
iterator erase( iterator pos );
iterator erase( const_iterator pos );
// (2) Non const version only
iterator erase( const_iterator first, const_iterator last );
// (3) Non const version only
size_type erase( const Key& key );
// (4) Non const version only
template< class K >
size_type erase( K&& x );
// (1) Non const version only
iterator erase( iterator pos );
iterator erase( const_iterator pos );
// (2) Non const version only
iterator erase( const_iterator first, const_iterator last );
// (3) Non const version only
size_type erase( const Key& key );
- (1) Removes the element at
pos
. Only one overload is provided ifiterator
andconst_iterator
are the same type. - (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
. - (4) Removes the element (if one exists) with key that compares equivalent to the value
x
. This overload participates in overload resolution only ifHash::is_transparent
andKeyEqual::is_transparent
are valid and each denotes a type, and neitheriterator
norconst_iterator
is implicitly convertible fromK
. This assumes that such Hash is callable with bothK
andKey
type, and that theKeyEqual
is transparent, which, together, allows calling this function without constructing an instance ofKey
.
The order of the elements that are not erased is preserved. (This makes it possible to erase individual elements while iterating through the container.)
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
.
Parameters
pos
- iterator to the element to removefirst, last
- range of elements to removekey
- key value of the elements to removex
- a value of any type that can be transparently compared with a key denoting the elements to remove
Return value
- (1-2) - Iterator following the last removed element.
- (3-4) - Number of elements removed (0 or 1).
Complexity
-
(1)
Average case: Constant
Worst case: Linear in the size of the container -
(2)
Average case: Linear instd::distance(first, last)
Worst case: Linear in the size of the container -
(3)
Average case:c.count(key)
Worst case: Linear in the size of the container -
(4)
Average case:c.count(x)
Worst case: Linear in the size of the container
Exceptions
- (1-2) (none)
- (3-4) Any exceptions thrown by the
Hash
andKeyEqual
object.
Notes
Feature testing macro: __cpp_lib_associative_heterogeneous_erasure
(for overload (4)).
Example
#include <unordered_set>
#include <iostream>
int main()
{
std::unordered_set<int> c = { 1, 2, 3, 4, 1, 2, 3, 4 };
auto print = [&c] {
std::cout << "c = { ";
for(int n : c)
std::cout << n << ' ';
std::cout << "}\n";
};
print();
std::cout << "Erase all odd numbers:\n";
for(auto it = c.begin(); it != c.end(); ) {
if(*it % 2 != 0)
it = c.erase(it);
else
++it;
}
print();
std::cout << "Erase 1, erased count: " << c.erase(1) << '\n';
std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
print();
}
c = { 1 2 3 4 }
Erase all odd numbers:
c = { 2 4 }
Erase 1, erased count: 0
Erase 2, erased count: 1
Erase 2, erased count: 0
c = { 4 }
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