Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::multimap::find(3)	      C++ Standard Libary	std::multimap::find(3)

NAME
       std::multimap::find - std::multimap::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. If	there are sev-
       eral elements with
	  key in the container,	any of them may	be returned.
	  3,4) Finds an	element	with key that compares equivalent to the value
       x. This
	  overload participates	in overload resolution only if the  qualified-
       id
	  Compare::is_transparent is valid and denotes a type. It allows call-
       ing 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  ele-
       ment is found,
	  past-the-end (see end()) iterator is returned.

Complexity
	  Logarithmic in the size of the container.

Notes
	  Feature-test	macro: __cpp_lib_generic_associative_lookup (for over-
       loads (3,4))

Example
       // Run this code

	#include <iostream>
	#include <map>

	struct FatKey	{ int x; int data[1000]; };
	struct LightKey	{ int x; };
	// Note: as detailed above, the	container  must	 use  std::less<>  (or
       other
	//   transparent Comparator) to	access these overloads.
	//  This  includes standard overloads, such as 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::multimap<int,char> example = {{1,'a'},{2,'b'}};

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

	// transparent comparison demo
	    std::multimap<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";
	    }
	// Obtaining const iterators.
	// Compiler decides whether to return iterator of (non)	const type  by
       way of accessing
	//  map; to prevent modification on purpose, one of easiest choices is
       to access map by
	// const reference.
	    const auto&	example2ref = example2;
	    auto search3 = example2ref.find(lk);
	    if (search3	!= example2.end()) {
		std::cout  <<  "Found  "  <<  search3->first.x	<<  '	'   <<
       search3->second << '\n';
	    //	search3->second	= 'c'; // error: assignment of member
				       // 'std::pair<const FatKey, char>::sec-
       ond'
				       // in read-only object
	    }
	}

Output:
	Found 2	b
	Found 2	b
	Found 2	b

See also
	  count	      returns the number of elements matching specific key
		      (public member function)
	  equal_range returns range of elements	matching a specific key
		      (public member function)

http://cppreference.com		  2022.07.31		std::multimap::find(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::multimap::find&sektion=3&manpath=FreeBSD+Ports+15.0>

home | help