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std::map::at(3) C++ Standard Libary std::map::at(3) NAME std::map::at - std::map::at Synopsis T& at( const Key& key ); (1) const T& at( const Key& key ) const; (2) template< class K > (3) (since C++26) T& at( const K& x ); template< class K > (4) (since C++26) const T& at( const K& x ) const; Returns a reference to the mapped value of the element with speci- fied key. If no such element exists, an exception of type std::out_of_range is thrown. 1,2) The key is equivalent to key. 3,4) The key compares equivalent to the value x. The reference to the mapped value is obtained as if by expression this->find(x)->second. The expression this->find(x) must be well-formed and have well-de- fined behavior, otherwise the behavior is undefined. These overloads participate in overload resolution only if the qual- ified-id Compare::is_transparent is valid and denotes a type. It allows call- ing this function without constructing an instance of Key. Parameters key - the key of the element to find x - a value of any type that can be transparently compared with a key Return value A reference to the mapped value of the requested element. Exceptions 1,2) std::out_of_range if the container does not have an element with the specified key. 3,4) std::out_of_range if the container does not have the specified element, that is, if find(x) == end() is true. Complexity Logarithmic in the size of the container. Notes Feature-test macro Value Std Feature Het- erogeneous over- loads for the re- maining member __cpp_lib_associative_heterogeneous_insertion 202311L (C++26) func- tions in ordered and unordered asso- ciative con- tainers. (3,4) Example This section is incomplete Reason: no example 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 464 C++98 map did not have this member function added LWG 703 C++98 the complexity requirement was missing added LWG 2007 C++98 the return value referred to the requested refers to its mapped element value See also operator[] access or insert specified element (public member function) Category: * Todo no example http://cppreference.com 2024.06.10 std::map::at(3)
NAME | Synopsis | Parameters | Return value | Exceptions | Complexity | Notes | Example | See also | Category:
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