std::set<Key,Compare,Allocator>::find - cppreference.com (original) (raw)
| iterator find( const Key& key ); | (1) | (constexpr since C++26) |
|---|---|---|
| const_iterator find( const Key& key ) const; | (2) | (constexpr since C++26) |
| template< class K >iterator find( const K& x ); | (3) | (since C++14) (constexpr since C++26) |
| template< class K >const_iterator find( const K& x ) const; | (4) | (since C++14) (constexpr since C++26) |
1,2) Finds an element with key equivalent to key.
3,4) Finds an element with key that compares equivalent to x.
This overload participates in overload resolution only if Compare is transparent. It allows calling this function without constructing an instance of Key.
[edit] Parameters
| key | - | key value of the element to search for |
|---|---|---|
| x | - | a value of any type that can be transparently compared with a key |
[edit] Return value
An iterator to the requested element. If no such element is found, past-the-end (see end()) iterator is returned.
[edit] Complexity
Logarithmic in the size of the container.
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
| __cpp_lib_generic_associative_lookup | 201304L | (C++14) | Heterogeneous comparison lookup in associative containers; overloads (3,4) |
[edit] Example
#include #include struct LightKey { int x; }; struct FatKey { int x; int data[1000]; // a heavy blob }; // As detailed above, the container must use std::less<> (or other transparent // Comparator) to access these overloads. This includes standard overloads, // such as comparison between std::string and std::string_view. bool operator<(const FatKey& fk, const LightKey& lk) { return fk.x < lk.x; } bool operator<(const LightKey& lk, const FatKey& fk) { return lk.x < fk.x; } bool operator<(const FatKey& fk1, const FatKey& fk2) { return fk1.x < fk2.x; } int main() { // Simple comparison demo. std::set example{1, 2, 3, 4}; if (auto search = example.find(2); search != example.end()) std::cout << "Found " << (*search) << '\n'; else std::cout << "Not found\n"; // Transparent comparison demo. std::set<FatKey, std::less<>> example2{{1, {}}, {2, {}}, {3, {}}, {4, {}}}; LightKey lk = {2}; if (auto search = example2.find(lk); search != example2.end()) std::cout << "Found " << search->x << '\n'; else std::cout << "Not found\n"; }
Output:
[edit] See also
| | returns the number of elements matching specific key (public member function) [edit] | | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns range of elements matching a specific key (public member function) [edit] |