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# std::multimap::equal_range

From cppreference.com
< cpp‎ | container‎ | multimap

[edit template]

std::pair<iterator,iterator> equal_range( const Key& key ); | (1) |
std::pair<const_iterator,const_iterator> equal_range( const Key& key ) const; | (2) |
template< class K > std::pair<iterator,iterator> equal_range( const K& x ); | (3) | (since C++14)
template< class K > std::pair<const_iterator,const_iterator> equal_range( const K& x ) const; | (4) | (since C++14)

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 only participates in overload resolution if the qualified-id Compare::is_transparent is valid and denotes a type. They allow calling this function without constructing an instance of `Key`.

| This section is incomplete Reason: explain better

### [edit] Parameters

key | - | key value to compare the elements to
x | - | alternative value that can be compared to `Key`

### [edit] 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.

Since insert always inserts at the upper bound, the order of equivalent elements in the equal range is the order of insertion. | (since C++11)

### [edit] Complexity

Logarithmic in the size of the container.

### [edit] Example

Run this code

    #include <iostream>
    #include <map>

    int main()
    {
        std::multimap<int, char> dict {
            {1, 'A'},
            {2, 'B'},
            {2, 'C'},
            {2, 'D'},
            {4, 'E'},
            {3, 'F'}
        };

        auto range = dict.equal_range(2);

        for (auto i = range.first; i != range.second; ++i)
        {
            std::cout << i->first << ": " << i->second << '\n';
        }
    }

Output:

    2: B
    2: C
    2: D

### [edit] See also

find | finds element with specific key (public member function) [edit]
upper_bound | returns an iterator to the first element greater than the given key (public member function) [edit]
lower_bound | returns an iterator to the first element not less than the given key (public member function) [edit]

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