std::flat_map<Key,T,Compare,KeyContainer,MappedContainer>::keys

 

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)

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Diagnostics library

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Strings library

Containers library

Iterators library

Ranges library (C++20)

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Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

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)

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std::flat_map

Member types

Member functions

flat_map::flat_map flat_map::operator= Element access flat_map::at flat_map::operator[] Iterators flat_map::beginflat_map::cbegin flat_map::endflat_map::cend flat_map::rbeginflat_map::crbegin flat_map::rendflat_map::crend Lookup flat_map::count flat_map::find flat_map::contains flat_map::equal_range    flat_map::lower_bound flat_map::upper_bound Capacity flat_map::size flat_map::max_size flat_map::empty Modifiers flat_map::clear flat_map::erase flat_map::swap flat_map::emplace flat_map::extract flat_map::replace flat_map::insert flat_map::insert_range flat_map::insert_or_assign flat_map::emplace_hint flat_map::try_emplace Observers flat_map::key_comp flat_map::keys flat_map::value_comp flat_map::values

Non-member functions

operator==operator<=>         swap(std::flat_map) erase_if(std::flat_map)

Helper classes

uses_allocator<std::flat_map>

Tags

sorted_unique       sorted_unique_t

Deduction guides

 

const key_container_type& keys() const noexcept;		(since C++23)

Return a constant reference to the adapted keys container. Equivalent to return c.keys;.

Parameters

(none)

Return value

The underlying keys container.

Complexity

Constant.

Example

Run this code

#include <flat_map>
#include <print>
#include <type_traits>
#include <vector>
 
int main()
{
    std::flat_map<int, double> adaptor{{1, 1.1}, {2, 2.2}, {3, 3.3}};
 
    // The default keys container is std::vector:
    static_assert(std::is_same_v<decltype(adaptor.keys()), const std::vector<int>&>);
 
    std::println("{}", adaptor.keys());
}

Output:

[1, 2, 3]

See also

values

direct access to the underlying values container (public member function)