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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 re-
       maining 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
       iterator	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_trans-
       parent and
	  KeyEqual::is_transparent are valid and each denotes a	type, and nei-
       ther 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	trans-
       parent, which,
	  together,  allows  calling this function without constructing	an in-
       stance 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()
       iterator	(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
       Feature
								      Hetero-
       geneous erasure in
								      associa-
       tive containers
	  __cpp_lib_associative_heterogeneous_erasure 202110L (C++23) and  un-
       ordered
								      associa-
       tive 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		  Cor-
       rect behavior
	  LWG  2059  C++11	 there was ambiguity for overload (2)	 added
       overload	(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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