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      std::unordered_set<Key,Hash,KeyEqual,Allocator>::erase

      From cppreference.com
      <cpp‎ |container‎ |unordered set

      [edit template]
       
       
       
      std::unordered_set
      Member types
      Member functions
      Non-member functions
      Deduction guides(C++17)
       
      (1)
      iterator erase( iterator pos);
      		(since C++11)
      (until C++23)
      iterator erase( iterator pos)
          requires(!std::same_as<iterator, const_iterator>);
      		(since C++23)
      (constexpr since C++26)
      iterator erase( const_iterator pos);
      		 (2)(since C++11)
      (constexpr since C++26)
      iterator erase( const_iterator first, const_iterator last);
      		 (3)(since C++11)
      (constexpr since C++26)
      size_type erase(const Key& key);
      		 (4)(since C++11)
      (constexpr since C++26)
      template<class K>
      size_type erase( K&& x);
      		 (5)(since C++23)
      (constexpr since C++26)

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

      1,2) Removes the element atpos.
      Only one overload is provided ifiterator andconst_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 tokey.
      5) Removes all elements with key that compares equivalent to the valuex.
      This overload participates in overload resolution only ifHash andKeyEqual are bothtransparent, and neitheriterator norconst_iterator is implicitly convertible fromK. This assumes that suchHash is callable with bothK andKey type, and that theKeyEqual is transparent, which, together, allows calling this function without constructing an instance ofKey.

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

      The iteratorpos must be dereferenceable. Thus theend() iterator (which is valid, but is not dereferenceable) cannot be used as a value forpos.

      Contents

      [edit]Parameters

      pos - iterator to the element to remove
      first, last - the pair of iterators defining therange 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

      [edit]Return value

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

      [edit]Exceptions

      1-3) Throws nothing.
      4,5) Any exceptions thrown by theHash andKeyEqual object.

      [edit]Complexity

      Given an instancec ofunordered_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 macroValueStdFeature
      __cpp_lib_associative_heterogeneous_erasure202110L(C++23)Heterogeneous erasure inassociative containers andunordered associative containers; overload(5)

      [edit]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();}

      Possible output:

      c = { 1 2 3 4 }Erase all odd numbers:c = { 2 4 }Erase 1, erased count: 0Erase 2, erased count: 1Erase 2, erased count: 0c = { 4 }

      Defect reports

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

      DRApplied toBehavior as publishedCorrect behavior
      LWG 2059C++11there was ambiguity for overload(2)added overload(1)
      LWG 2356C++11the order of non-equivalent elements that are
      not erased was not guaranteed to be preserved      		required to be preserved

      [edit]See also

      clears the contents
      (public member function)[edit]
      Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/container/unordered_set/erase&oldid=125831"
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