std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::at

 

C++

Compiler support

Freestanding and hosted

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

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

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

 

std::unordered_map

Member types

Member functions

unordered_map::unordered_map

unordered_map::~unordered_map

unordered_map::operator=

unordered_map::get_allocator

Iterators

unordered_map::beginunordered_map::cbegin

unordered_map::endunordered_map::cend

Capacity

unordered_map::empty

unordered_map::size

unordered_map::max_size

Modifiers

unordered_map::clear

unordered_map::insert

unordered_map::insert_range (C++23)

unordered_map::insert_or_assign (C++17)

unordered_map::emplace

unordered_map::emplace_hint

unordered_map::try_emplace (C++17)

unordered_map::erase

unordered_map::swap

unordered_map::extract (C++17)

unordered_map::merge (C++17)

Lookup

unordered_map::at

unordered_map::operator[]

unordered_map::count

unordered_map::find

unordered_map::contains (C++20)

unordered_map::equal_range

Bucket interface

unordered_map::begin(size_type)unordered_map::cbegin(size_type)

unordered_map::end(size_type)unordered_map::cend(size_type)

unordered_map::bucket_count

unordered_map::max_bucket_count

unordered_map::bucket_size

unordered_map::bucket

Hash policy

unordered_map::load_factor

unordered_map::max_load_factor

unordered_map::rehash

unordered_map::reserve

Observers

unordered_map::hash_function

unordered_map::key_eq

Non-member functions

operator==operator!= (until C++20)

std::swap

erase_if (C++20)

Deduction guides(C++17)

 

T& at( const Key& key );	(1)	(since C++11)
const T& at( const Key& key ) const;	(2)	(since C++11)

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

Average case: constant, worst case: linear in size.

See also

operator[] (C++11)

access or insert specified element (public member function)