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std::set::emplace_hint(3)     C++ Standard Libary    std::set::emplace_hint(3)

NAME
       std::set::emplace_hint -	std::set::emplace_hint

Synopsis
	  template<		   class...		  Args		     >
       (since C++11)
	  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)....

	  No iterators or references are invalidated.

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
	  Logarithmic  in  the size of the container in	general, but amortized
       constant	if the
	  new element is inserted just before hint.

Example
       // Run this code

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

	const int n_operations = 100'500'0;

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

	std::size_t set_emplace_hint()
	{
	    std::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::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::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::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:
	392.25ms for plain emplace (ratio: 1.00)
	 97.15ms for emplace with correct hint (ratio: 4.04)
	387.52ms for emplace with wrong	hint (ratio: 1.01)
	 84.80ms for corrected emplace (ratio: 4.63)
	 83.67ms for emplace using returned iterator (ratio: 4.69)

See also
	  emplace constructs element in-place
	  (C++11) (public member function)
		  inserts elements
	  insert  or nodes
		  (since C++17)
		  (public member function)

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

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