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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 specified
     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-defined
     behavior,
	otherwise the behavior is undefined.
	These overloads participate in overload resolution only  if  the  quali-
     fied-id
	Compare::is_transparent  is  valid and denotes a type. It allows calling
     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 ele-
     ment, that
	is, if find(x) == end() is true.

Complexity
	Logarithmic in the size of the container.

Notes
		     Feature-test      macro			Value	     Std
     Feature
								      Heteroge-
     neous
								      overloads
     for the
								      remaining
     member
	__cpp_lib_associative_heterogeneous_insertion 202311L (C++26)  functions
     in ordered
								      and    un-
     ordered
								      associa-
     tive
								      contain-
     ers. (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		    Cor-
     rect 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)
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