std::multimap::equal_range
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
. The first iterator may be alternatively obtained with lower_bound(), the second  with upper_bound().
key
.x
. These templates only participate in overload resolution if the type Compare::is_transparent exists. They allow calling this function without constructing an instance of Key
. This section is incomplete Reason: explain better 
Contents 
[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
, pasttheend (see end()) iterator is returned as the first element. Similarly if there are no elements greater than key
, pasttheend iterator is returned as the second element.
Since insert always inserts at the upper bound, the order of equivalent elements is the equal range is the order of insertion.  (since C++11) 
[edit] Complexity
Logarithmic in the size of the container.
[edit] Example
This section is incomplete Reason: no example 
[edit] See also
finds element with specific key (public member function)  
returns an iterator to the first element greater than a certain value (public member function)  
returns an iterator to the first element not less than the given value (public member function) 