public member function
<map>
std::map::equal_range
pair<const_iterator,const_iterator> equal_range (const key_type& k) const;
pair<iterator,iterator> equal_range (const key_type& k);
Get range of equal elements
Returns the bounds of a range that includes all the elements in the container which have a key equivalent to k.
Because the elements in a map container have unique keys, the range returned will contain a single element at most.
If no matches are found, the range returned has a length of zero, with both iterators pointing to the first element that has a key considered to go after k according to the container's internal comparison object (key_comp).
Two keys are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the keys are passed as arguments).
Parameters
- k
- Key to search for.
Member type key_type is the type of the elements in the container, defined in map as an alias of its first template parameter (Key).
Return value
The function returns a pair, whose member pair::first is the lower bound of the range (the same as lower_bound), and pair::second is the upper bound (the same as upper_bound).
If the map object is const-qualified, the function returns a pair of const_iterator. Otherwise, it returns a pair of iterator.
Member types iterator and const_iterator are bidirectional iterator types pointing to elements (of type value_type).
Notice that value_type in map containers is itself also a pair type: pair<const key_type, mapped_type>.
Example
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|
// map::equal_range
#include <iostream>
#include <map>
int main ()
{
std::map<char,int> mymap;
mymap['a']=10;
mymap['b']=20;
mymap['c']=30;
std::pair<std::map<char,int>::iterator,std::map<char,int>::iterator> ret;
ret = mymap.equal_range('b');
std::cout << "lower bound points to: ";
std::cout << ret.first->first << " => " << ret.first->second << '\n';
std::cout << "upper bound points to: ";
std::cout << ret.second->first << " => " << ret.second->second << '\n';
return 0;
}
| |
lower bound points to: 'b' => 20
upper bound points to: 'c' => 30
|
Complexity
Logarithmic in size.
Iterator validity
No changes.
Data races
The container is accessed (neither the const nor the non-const versions modify the container).
No mapped values are accessed: concurrently accessing or modifying elements is safe.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container.
See also
- map::count
- Count elements with a specific key (public member function
)
- map::lower_bound
- Return iterator to lower bound (public member function
)
- map::upper_bound
- Return iterator to upper bound (public member function
)
- map::operator[]
- Access element (public member function
)
- map::find
- Get iterator to element (public member function
)