std::set equal_range() method
- since C++14
- until C++14
// (1) Non const version
std::pair<iterator, iterator> equal_range( const Key& key );
// (2) Const version
std::pair<const_iterator, const_iterator> equal_range( const Key& key ) const;
// (3) Non const version
template< class K >
std::pair<iterator, iterator> equal_range( const K& x );
// (4) Const version
template< class K >
std::pair<const_iterator, const_iterator> equal_range( const K& x ) const;
// (1) Non const version
std::pair<iterator, iterator> equal_range( const Key& key );
// (2) Const version
std::pair<const_iterator, const_iterator> equal_range( const Key& key ) const;
Returns a range containing all elements with the given key in the container.
The range is defined by two iterators, one pointing to the first element that is not less than key and another pointing to the first element greater than key.
Alternatively, the first iterator may be obtained with lower_bound()
, and the second with upper_bound()
.
- (1-2) Compares the keys to
key
. - (3-4) Compares the keys to the value
x
. This overload participates in overload resolution only if the qualified-idCompare::is_transparent
is valid and denotes a type. It allows calling this function without constructing an instance ofKey
.
Parameters
key
- key value to compare the elements tox
- alternative value that can be compared to Key
Return value
std::pair
containing a pair of iterators defining the wanted range: the first pointing to the first element that is not less than key
and the second pointing to the first element greater than key.
If there are no such elements, past-the-end (see end()
) iterators are returned as both elements of the pair.
Complexity
Logarithmic in the size of the container - O(log size()).
Exceptions
(none)
Notes
Feature testing macro: __cpp_lib_generic_unordered_lookup
(for overload (3-4)).
Example
#include <set>
#include <iostream>
template <typename I>
void print_equal_range(I first, I lb, I ub, I last) {
for (I i{first}; i != lb; ++i)
std::cout << *i << " ";
std::cout << "[ ";
for (I i{lb}; i != ub; ++i)
std::cout << *i << " ";
std::cout << ") ";
for (I i{ub}; i != last; ++i)
std::cout << *i << " ";
std::cout << '\n';
}
int main()
{
std::set<int> c{4, 3, 2, 1, 3, 3};
std::cout << "c = ";
print_equal_range(begin(c), begin(c), end(c), end(c));
for (int key{}; key != 6; ++key) {
std::cout << "key = " << key << "; equal range = ";
const auto [lb, ub] = c.equal_range(key);
print_equal_range(begin(c), lb, ub, end(c));
}
}
c = [ 1 2 3 4 )
key = 0; equal range = [ ) 1 2 3 4
key = 1; equal range = [ 1 ) 2 3 4
key = 2; equal range = 1 [ 2 ) 3 4
key = 3; equal range = 1 2 [ 3 ) 4
key = 4; equal range = 1 2 3 [ 4 )
key = 5; equal range = 1 2 3 4 [ )
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