std::flat_map<Key,T,Compare,KeyContainer,MappedContainer>::equal_range

 

C++

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Feature test macros (C++20)

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Ranges library (C++20)

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Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

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span (C++20)

mdspan (C++23)

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std::flat_map

Member types

Member functions

flat_map::flat_map flat_map::operator= Element access flat_map::at flat_map::operator[] Iterators flat_map::beginflat_map::cbegin flat_map::endflat_map::cend flat_map::rbeginflat_map::crbegin flat_map::rendflat_map::crend Lookup flat_map::count flat_map::find flat_map::contains flat_map::equal_range    flat_map::lower_bound flat_map::upper_bound Capacity flat_map::size flat_map::max_size flat_map::empty Modifiers flat_map::clear flat_map::erase flat_map::swap flat_map::emplace flat_map::extract flat_map::replace flat_map::insert flat_map::insert_range flat_map::insert_or_assign flat_map::emplace_hint flat_map::try_emplace Observers flat_map::key_comp flat_map::keys flat_map::value_comp flat_map::values

Non-member functions

operator==operator<=>         swap(std::flat_map) erase_if(std::flat_map)

Helper classes

uses_allocator<std::flat_map>

Tags

sorted_unique       sorted_unique_t

Deduction guides

 

std::pair<iterator, iterator> equal_range( const Key& key );	(1)	(since C++23)
std::pair<const_iterator, const_iterator> equal_range( const Key& key ) const;	(2)	(since C++23)
template< class K > std::pair<iterator, iterator> equal_range( const K& x );	(3)	(since C++23)
template< class K > std::pair<const_iterator, const_iterator> equal_range( const K& x ) const;	(4)	(since C++23)

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-id Compare::is_transparent is valid and denotes a type. It allows calling this function without constructing an instance of Key.

Parameters

key	-	key value to compare the elements to
x	-	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 elements not less than key, past-the-end (see end()) iterator is returned as the first element. Similarly if there are no elements greater than key, past-the-end iterator is returned as the second element.

Complexity

Logarithmic in the size of the container.

Example

Run this code

#include <iostream>
#include <flat_map>
 
int main()
{
    const std::flat_map<int, const char*> m
    {
        {0, "zero"},
        {1, "one"},
        {2, "two"}
    };
 
    auto p = m.equal_range(1);
    for (auto& q = p.first; q != p.second; ++q)
        std::cout << "m[" << q->first << "] = " << q->second << '\n';
 
    if (p.second == m.find(2))
        std::cout << "end of equal_range (p.second) is one-past p.first\n";
    else
        std::cout << "unexpected; p.second expected to be one-past p.first\n";
 
    auto pp = m.equal_range(-1);
    if (pp.first == m.begin())
        std::cout << "pp.first is iterator to first not-less than -1\n";
    else
        std::cout << "unexpected pp.first\n";
 
    if (pp.second == m.begin())
        std::cout << "pp.second is iterator to first element greater-than -1\n";
    else
        std::cout << "unexpected pp.second\n";
 
    auto ppp = m.equal_range(3);
    if (ppp.first == m.end())
        std::cout << "ppp.first is iterator to first not-less than 3\n";
    else
        std::cout << "unexpected ppp.first\n";
 
    if (ppp.second == m.end())
        std::cout << "ppp.second is iterator to first element greater-than 3\n";
    else
        std::cout << "unexpected ppp.second\n";
}

Output:

m[1] = one
end of equal_range (p.second) is one-past p.first
pp.first is iterator to first not-less than -1
pp.second is iterator to first element greater-than -1
ppp.first is iterator to first not-less than 3
ppp.second is iterator to first element greater-than 3

See also

find	finds element with specific key (public member function)
contains	checks if the container contains element with specific key (public member function)
count	returns the number of elements matching specific key (public member function)
upper_bound	returns an iterator to the first element greater than the given key (public member function)
lower_bound	returns an iterator to the first element not less than the given key (public member function)
equal_range	returns range of elements matching a specific key (function template)