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std::unordered_map::erase(3) C++ Standard Libary std::unordered_map::erase(3) NAME std::unordered_map::erase - std::unordered_map::erase Synopsis iterator erase( iterator pos ); (since C++11) iterator erase( const_iterator pos ); (since C++11) iterator erase( const_iterator first, (since C++11) const_iterator last ); (1) size_type erase( const Key& key ); (2) (3) (since C++11) template< class K > (4) (since C++23) size_type erase( K&& x ); Removes specified elements from the container. 1) Removes the element at pos. 2) Removes the elements in the range [first; last), which must be a valid range in *this. 3) Removes the element (if one exists) with the key equivalent to key. 4) Removes the element (if one exists) with key that compares equiv- alent to the value x. This overload participates in overload resolution only if Hash::is_transparent 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 with- out 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() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos. The order of the elements that are not erased is preserved. (This makes it possible to erase individual elements while iterating through the container.) 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 1-2) Iterator following the last removed element. 3,4) Number of elements removed (0 or 1). Exceptions 1,2) Throws nothing. 3,4) Any exceptions thrown by the Hash and KeyEqual object. Complexity Given an instance c of unordered_map: 1) Average case: constant, worst case: c.size() 2) Average case: std::distance(first, last), worst case: c.size() 3) Average case: c.count(key), worst case: c.size() 4) Average case: c.count(x), worst case: c.size() Notes Feature-test macro: __cpp_lib_associative_heterogeneous_erasure (for overload (4)) Example // Run this code #include <unordered_map> #include <iostream> int main() { std::unordered_map<int, std::string> c = { {1, "one" }, {2, "two" }, {3, "three"}, {4, "four"}, {5, "five"}, {6, "six" } }; // erase all odd numbers from c for(auto it = c.begin(); it != c.end(); ) { if(it->first % 2 != 0) it = c.erase(it); else ++it; } for(auto& p : c) { std::cout << p.second << ' '; } } Possible output: two four six 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 overload for one const_iterator introduced over- load for iterator new ambiguity added LWG 2356 C++11 the order of element that are not erased re- quired to be was unspecified pre- served See also clear clears the contents (C++11) (public member function) http://cppreference.com 2022.07.31 std::unordered_map::erase(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Complexity | Notes | Example | Possible output: | See also
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