std::flat_set<Key,Compare,KeyContainer>::equal_range

 

C++

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Technical specifications

Symbols index

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Containers library

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

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forward_list (C++11)

list

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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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flat_set (C++23)

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flat_map (C++23)

flat_multimap (C++23)

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span (C++20)

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std::flat_set

Member types

Member functions

flat_set::flat_set flat_set::operator= Iterators flat_set::beginflat_set::cbegin flat_set::endflat_set::cend flat_set::rbeginflat_set::crbegin flat_set::rendflat_set::crend Capacity flat_set::size flat_set::max_size flat_set::empty Observers flat_set::key_comp flat_set::value_comp      Modifiers flat_set::clear flat_set::insert flat_set::insert_range flat_set::emplace flat_set::emplace_hint flat_set::erase flat_set::swap flat_set::extract flat_set::replace Lookup flat_set::count flat_set::find flat_set::contains flat_set::equal_range flat_set::lower_bound flat_set::upper_bound Non-member functions operator==operator<=> swap(std::flat_set) erase_if(std::flat_set)

Helper classes

uses_allocator<std::flat_set>

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 <flat_set>
#include <functional>
#include <print>
#include <ranges>
#include <string>
#include <string_view>
#include <tuple>
 
struct Names
{
    std::string forename, surname;
    friend auto operator<(const Names& lhs, const Names& rhs)
    {
        return std::tie(lhs.surname, lhs.forename) < std::tie(rhs.surname, rhs.forename);
    }
};
 
struct SurnameCompare
{
    std::string_view surname;
 
    friend bool operator<(const Names& lhs, const SurnameCompare& rhs)
    {
        return lhs.surname < rhs.surname;
    }
 
    friend bool operator<(const SurnameCompare& lhs, const Names& rhs)
    {
        return lhs.surname < rhs.surname;
    }
}; 
 
std::set<Names, std::less<>> characters
{
    {"Homer", "Simpson"},
    {"Marge", "Simpson"},
    {"Lisa", "Simpson"},
    {"Ned", "Flanders"},
    {"Joe", "Quimby"}
};
 
void print_unique(const Names& names)
{
    auto [begin, end] = characters.equal_range(names);
    std::print(
        "Found {} characters with name \"{} {}\"\n", 
        std::distance(begin, end), 
        names.forename, names.surname
    );
}
 
void print_by_surname(std::string_view surname)
{
    auto [begin, end] = characters.equal_range(SurnameCompare{surname});
    std::print("Found {} characters with surname \"{}\":\n", std::distance(begin, end), surname);
    for (const Names& names : std::ranges::subrange(begin, end))
        std::print("    {} {}\n", names.forename, names.surname);
}
 
int main()
{
    print_unique({"Maude", "Flanders"});
    print_unique({"Lisa", "Simpson"});
    print_by_surname("Simpson");
}

Output:

Found 0 characters with name "Maude Flanders"
Found 1 characters with name "Lisa Simpson"
Found 3 characters with surname "Simpson":
    Homer Simpson
    Lisa Simpson
    Marge Simpson

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)