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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 ); (1) (since C++11) iterator erase( const_iterator pos ); (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. 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_map: 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_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 << ' '; std::cout << '\n'; } 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 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_map::erase(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Complexity | Notes | Example | Possible output: | See also
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