From cppreference.com
iteratorfind(constKey&key); (1) (since C++11)const_iteratorfind(constKey&key)const; (2) (since C++11)template<classK>iteratorfind(constK&x); (3)(since C++20)template<classK>const_iteratorfind(constK&x)const; (4)(since C++20)1,2) Finds an element with key equivalent to key.
3,4) Finds an element with key that compares equivalent to the value x. This overload participates in overload resolution only if Hash::is_transparent and KeyEqual::is_transparent are valid and each denotes a type. This assumes that such Hash is callable with both K and Key type, and that the KeyEqual is transparent, which, together, allows calling this function without constructing an instance of Key.
Parameters
key - key value of the element to search for x - a value of any type that can be transparently compared with a key Return value
An iterator to the requested element. If no such element is found, past-the-end (see
) iterator is returned.
Complexity
Constant on average, worst case linear in the size of the container.
Notes
macroValueStdFeature
__cpp_lib_generic_unordered_lookup
(C++20)Heterogeneous comparison lookup in
unordered associative containers
; overloads (
)Example
Run this code
#include<cstddef>#include<functional>#include<iostream>#include<string>#include<string_view>#include<unordered_map>usingnamespacestd::literals;structstring_hash{usinghash_type=std::hash<std::string_view>;usingis_transparent=void;std::size_toperator()(constchar*str)const{returnhash_type{}(str);}std::size_toperator()(std::string_viewstr)const{returnhash_type{}(str);}std::size_toperator()(std::stringconst&str)const{returnhash_type{}(str);}};intmain(){// simple comparison demostd::unordered_map<int,char>example{{1,'a'},{2,'b'}};if(autosearch=example.find(2);search!=example.end())std::cout<<"Found "<<search->first<<' '<<search->second<<'\n';elsestd::cout<<"Not found\n";// C++20 demo: Heterogeneous lookup for unordered containers (transparent hashing)std::unordered_map<std::string,size_t,string_hash,std::equal_to<>>map{{"one"s,1}};std::cout<<std::boolalpha<<(map.find("one")!=map.end())<<'\n'<<(map.find("one"s)!=map.end())<<'\n'<<(map.find("one"sv)!=map.end())<<'\n';}Output:
Found 2 b true true true See also
access specified element with bounds checking
(public member function)
access or insert specified element
(public member function)
returns the number of elements matching specific key
(public member function)
returns range of elements matching a specific key
(public member function)