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

FreeBSD Manual Pages

  
 
  

home | help 
std::flat_s...emplace_hint(3) C++ Standard Libarystd::flat_s...emplace_hint(3)

NAME
       std::flat_set::emplace_hint - std::flat_set::emplace_hint

Synopsis
	  template<		   class...		  Args		     >
       (since C++23)
	  iterator emplace_hint( const_iterator	hint, Args&&...	args );

	  Inserts a new	element	into the container as close as possible	to the
       position	just
	  before hint.

	  The constructors of the key and mapped value are called with exactly
       the same
	  arguments as supplied	to  the	 function,  forwarded  with  std::for-
       ward<Args>(args)....

	   Information on iterator invalidation	is copied from here

Parameters
	  hint - iterator to the position before which the new element will be
       inserted
	  args - arguments to forward to the constructor of the	element

Return value
	  An  iterator	to  the	 inserted element, or to the element that pre-
       vented the insertion.

Exceptions
	  If an	exception is thrown for	any reason, this function has  no  ef-
       fect (strong
	  exception safety guarantee).

Complexity
	   This	section	is incomplete

Example
       // Run this code

	#include <chrono>
	#include <cstddef>
	#include <functional>
	#include <iomanip>
	#include <iostream>
	#include <flat_set>

	const int n_operations = 100'500'0;

	std::size_t set_emplace()
	{
	    std::flat_set<int> set;
	    for	(int i = 0; i <	n_operations; ++i)
		set.emplace(i);
	    return set.size();
	}

	std::size_t set_emplace_hint()
	{
	    std::flat_set<int> set;
	    auto it = set.begin();
	    for	(int i = 0; i <	n_operations; ++i)
	    {
		set.emplace_hint(it, i);
		it = set.end();
	    }
	    return set.size();
	}

	std::size_t set_emplace_hint_wrong()
	{
	    std::flat_set<int> set;
	    auto it = set.begin();
	    for	(int i = n_operations; i > 0; --i)
	    {
		set.emplace_hint(it, i);
		it = set.end();
	    }
	    return set.size();
	}

	std::size_t set_emplace_hint_corrected()
	{
	    std::flat_set<int> set;
	    auto it = set.begin();
	    for	(int i = n_operations; i > 0; --i)
	    {
		set.emplace_hint(it, i);
		it = set.begin();
	    }
	    return set.size();
	}

	std::size_t set_emplace_hint_closest()
	{
	    std::flat_set<int> set;
	    auto it = set.begin();
	    for	(int i = 0; i <	n_operations; ++i)
		it = set.emplace_hint(it, i);
	    return set.size();
	}

	double time_it(std::function<std::size_t()> set_test,
		       const char* what	= nullptr,
		       double ratio = 0.0)
	{
	    const auto start = std::chrono::system_clock::now();
	    const std::size_t setsize =	set_test();
	    const auto stop = std::chrono::system_clock::now();
	    const  std::chrono::duration<double,  std::milli>  time  =	stop -
       start;
	    if (what !=	nullptr	&& setsize > 0)
		std::cout << std::setw(8) << time << " for " <<	what <<	" (ra-
       tio: "
			  << (ratio == 0.0 ? 1.0 : ratio  /  time.count())  <<
       ")\n";
	    return time.count();
	}

	int main()
	{
	    std::cout << std::fixed << std::setprecision(2);
	    time_it(set_emplace); // cache warmup
	    const auto x = time_it(set_emplace,	"plain emplace");
	    time_it(set_emplace_hint, "emplace with correct hint", x);
	    time_it(set_emplace_hint_wrong, "emplace with wrong	hint", x);
	    time_it(set_emplace_hint_corrected,	"corrected emplace", x);
	    time_it(set_emplace_hint_closest,  "emplace	 using returned	itera-
       tor", x);
	}

Possible output:
	...TODO...

See also
	  emplace constructs element in-place
		  (public member function)
	  insert  inserts elements
		  (public member function)

Category:
	    * Todo without reason

http://cppreference.com		  2024.06.10	 std::flat_s...emplace_hint(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::flat_set::emplace_hint&sektion=3&manpath=FreeBSD+Ports+15.1.quarterly>

home | help