std::map<Key,T,Compare,Allocator>::at

T& at( const Key& key );	(1)
const T& at( const Key& key ) const;	(2)

Returns a reference to the mapped value of the element with key equivalent to key. If no such element exists, an exception of type std::out_of_range is thrown.

Parameters

key

-

the key of the element to find

Return value

Reference to the mapped value of the requested element.

Exceptions

std::out_of_range if the container does not have an element with the specified key.

Complexity

Logarithmic in the size of the container.

Defect reports

The following behavior-changing defect reports were applied retroactively 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 element	refers to its mapped value

Compiler support
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Language
Standard library
Standard library headers
Named requirements
Feature test macros (C++20)
Language support library
Concepts library (C++20)
Metaprogramming library (C++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (C++20)
Algorithms library
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Filesystem library (C++17)
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Technical specifications
Symbols index
External libraries

Sequence
array (C++11)
vector
vector<bool>
deque
forward_list (C++11)
list
Associative
set
multiset
map
multimap
Unordered associative
unordered_set (C++11)
unordered_multiset (C++11)
unordered_map (C++11)
unordered_multimap (C++11)
Adaptors
stack
queue
priority_queue
flat_set (C++23)
flat_multiset (C++23)
flat_map (C++23)
flat_multimap (C++23)
Views
span (C++20)
mdspan (C++23)
Iterator invalidation
Member function table
Non-member function table

Member functions
map::map
map::~map
map::operator=
map::get_allocator
Element access
map::at
map::operator[]
Iterators
map::beginmap::cbegin (C++11)
map::endmap::cend (C++11)
map::rbeginmap::crbegin (C++11)
map::rendmap::crend (C++11)
Capacity
map::empty
map::size
map::max_size
Modifiers
map::clear
map::insert
map::insert_range (C++23)
map::insert_or_assign (C++17)
map::emplace (C++11)
map::emplace_hint (C++11)
map::try_emplace (C++17)
map::erase
map::swap
map::extract (C++17)
map::merge (C++17)
Lookup
map::count
map::find
map::contains (C++20)
map::equal_range
map::lower_bound
map::upper_bound
Observers
map::key_comp
map::value_comp
Non-member functions
std::swap
erase_if (C++20)
operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Deduction guides (C++17)