std::map<Key,T,Compare,Allocator>::find (3) - Linux Manuals

std::map<Key,T,Compare,Allocator>::find: std::map<Key,T,Compare,Allocator>::find

NAME

std::map<Key,T,Compare,Allocator>::find - std::map<Key,T,Compare,Allocator>::find

Synopsis

iterator find( const Key& key ); (1)
const_iterator find( const Key& key ) const; (2)
template< class K > iterator find( const K& x ); (3) (since C++14)
template< class K > const_iterator find( const K& x ) const; (4) (since C++14)

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 only participates in overload resolution if the qualified-id Compare::is_transparent is valid and denotes a type. It 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

Iterator to an element with key equivalent to key. If no such element is found, past-the-end (see end()) iterator is returned.

Complexity

Logarithmic in the size of the container.

Example

// Run this code

  #include <iostream>
  #include <map>
  struct FatKey { int x; int data[1000]; };
  struct LightKey { int x; };
  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::map<int,char> example = {{1,'a'},{2,'b'}};

      auto search = example.find(2);
      if (search != example.end()) {
          std::cout << "Found " << search->first << " " << search->second << '\n';
      } else {
          std::cout << "Not found\n";
      }

  // transparent comparison demo
      std::map<FatKey, char, std::less<>> example2 = { { {1, {} },'a'}, { {2, {} },'b'} };

      LightKey lk = {2};
      auto search2 = example2.find(lk);
      if (search2 != example2.end()) {
          std::cout << "Found " << search2->first.x << " " << search2->second << '\n';
      } else {
          std::cout << "Not found\n";
      }
  }

Output:

  Found 2 b
  Found 2 b