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std::unordered_set::erase(3)   C++ Standard Libary  std::unordered_set::erase(3)

NAME
     std::unordered_set::erase - std::unordered_set::erase

Synopsis
	iterator	    erase(	     iterator		pos	      );
     (since C++11)
									     (un-
     til C++23)
	iterator	   erase(	    iterator		pos	       )
     (since C++23)
	    requires(!std::same_as<iterator, const_iterator>);
	iterator  erase(  const_iterator  pos  );			 (1) (2)
     (since C++11)
	iterator erase( const_iterator first,  const_iterator  last  );      (3)
     (since C++11)
	size_type  erase(  const  Key&	key );				     (4)
     (since C++11)
	template<  class  K  >						     (5)
     (since C++23)
	size_type erase( K&& x );

	Removes  specified elements from the container. The order of the remain-
     ing elements
	is preserved. (This makes it possible to erase individual elements while
     iterating
	through the container.)

	1,2) Removes the element at pos. Only one overload is provided if itera-
     tor and
	const_iterator are the same type.
	3) Removes the elements in the range [first,  last),  which  must  be  a
     valid range in
	*this.
	4) Removes the element (if one exists) with the key equivalent to key.
	5)  Removes  all elements with key that compares equivalent to the value
     x. This
	overload participates in overload resolution only if  Hash::is_transpar-
     ent and
	KeyEqual::is_transparent  are valid and each denotes a type, and neither
     iterator nor
	const_iterator is implicitly convertible from K. This assumes that  such
     Hash is
	callable with both K and Key type, and that the KeyEqual is transparent,
     which,
	together,  allows calling this function without constructing an instance
     of Key.

	References and iterators to the erased elements are  invalidated.  Other
     iterators and
	references are not invalidated.

	The iterator pos must be valid and dereferenceable. Thus the end() iter-
     ator (which
	is valid, but is not dereferenceable) cannot be used as a value for pos.

Parameters
	pos	    - iterator to the element to remove
	first, last - range of elements to remove
	key	    - key value of the elements to remove
	x	     -	a  value  of any type that can be transparently compared
     with a key
		      denoting the elements to remove

Return value
	1-3) Iterator following the last removed element.
	4) Number of elements removed (0 or 1).
	5) Number of elements removed.

Exceptions
	1-3) Throws nothing.
	4,5) Any exceptions thrown by the Hash and KeyEqual object.

Complexity
	Given an instance c of unordered_set:

	1,2) Average case: constant, worst case: c.size().
	3) Average case: std::distance(first, last), worst case: c.size().
	4) Average case: c.count(key), worst case: c.size().
	5) Average case: c.count(x), worst case: c.size().

Notes
		    Feature-test macro		     Value    Std	    Fea-
     ture
								    Heteroge-
     neous erasure in
								    associative
     containers
	__cpp_lib_associative_heterogeneous_erasure  202110L  (C++23)  and   un-
     ordered
								    associative
     containers;
								    overload (5)

Example
     // Run this code

      #include <unordered_set>
      #include <iostream>

      int main()
      {
	  std::unordered_set<int> c = {1, 2, 3, 4, 1, 2, 3, 4};

	  auto print = [&c]
	  {
	      std::cout << "c = { ";
	      for (int n : c)
		  std::cout << n << ' ';
	      std::cout << "}\n";
	  };
	  print();

	  std::cout << "Erase all odd numbers:\n";
	  for (auto it = c.begin(); it != c.end();)
	  {
	      if (*it % 2 != 0)
		  it = c.erase(it);
	      else
		  ++it;
	  }
	  print();

	  std::cout << "Erase 1, erased count: " << c.erase(1) << '\n';
	  std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
	  std::cout << "Erase 2, erased count: " << c.erase(2) << '\n';
	  print();
      }

       Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to	     Behavior as published		 Correct
     behavior
	LWG  2059 C++11      there was ambiguity for overload (2)    added over-
     load (1)
			    the order of non-equivalent elements
	LWG 2356 C++11	    that are				    required  to
     be preserved
			    not erased was not guaranteed to be
			    preserved

See also
	clear clears the contents
	      (public member function)

http://cppreference.com 	   2024.06.10	    std::unordered_set::erase(3)
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