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

 

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)

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)

Tables

Iterator invalidation

Member function table

Non-member function table

 

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

 

flat_map()     : flat_map(key_compare()) { }	(1)	(since C++23)
template< class Allocator > flat_map( const flat_map&, const Allocator& alloc );	(2)	(since C++23)
template< class Allocator > flat_map( flat_map&&, const Allocator& alloc );	(3)	(since C++23)
flat_map( key_container_type key_cont, mapped_container_type mapped_cont,           const key_compare& comp = key_compare() );	(4)	(since C++23)
template< class Allocator > flat_map( const key_container_type& key_cont,           const mapped_container_type& mapped_cont,           const Allocator& alloc );	(5)	(since C++23)
template< class Allocator > flat_map( const key_container_type& key_cont,           const mapped_container_type& mapped_cont,           const key_compare& comp, const Allocator& alloc );	(6)	(since C++23)
flat_map( std::sorted_unique_t, key_container_type key_cont,           mapped_container_type mapped_cont,           const key_compare& comp = key_compare() );	(7)	(since C++23)
template< class Allocator > flat_map( std::sorted_unique_t, const key_container_type& key_cont,           const mapped_container_type& mapped_cont, const Allocator& alloc );	(8)	(since C++23)
template< class Allocator > flat_map( std::sorted_unique_t, const key_container_type& key_cont,           const mapped_container_type& mapped_cont,           const key_compare& comp, const Allocator& alloc );	(9)	(since C++23)
explicit flat_map( const key_compare& comp )     : c(), compare(comp) { }	(10)	(since C++23)
template< class Allocator > flat_map( const key_compare& comp, const Allocator& alloc );	(11)	(since C++23)
template< class Allocator > explicit flat_map( const Allocator& alloc );	(12)	(since C++23)
template< class InputIter > flat_map( InputIter first, InputIter last,           const key_compare& comp = key_compare() )     : c(), compare(comp);	(13)	(since C++23)
template< class InputIter, class Allocator > flat_map( InputIter first, InputIter last,           const key_compare& comp, const Allocator& alloc );	(14)	(since C++23)
template< class InputIter, class Allocator > flat_map( InputIter first, InputIter last, const Allocator& alloc );	(15)	(since C++23)
template< container-compatible-range<value_type> R > flat_map( std::from_range_t, R&& rg, const key_compare& comp )     : flat_map(comp);	(16)	(since C++23)
template< container-compatible-range<value_type> R > flat_map( std::from_range_t fr, R&& rg )     : flat_map(fr, std::forward<R>(rg), key_compare()) { }	(17)	(since C++23)
template< container-compatible-range<value_type> R, class Allocator > flat_map( std::from_range_t, R&& rg, const Allocator& alloc );	(18)	(since C++23)
template< container-compatible-range<value_type> R, class Allocator > flat_map( std::from_range_t, R&& rg, const key_compare& comp,           const Allocator& alloc );	(19)	(since C++23)
template< class InputIter > flat_map( std::sorted_unique_t s, InputIter first, InputIter last,           const key_compare& comp = key_compare() )     : c(), compare(comp);	(20)	(since C++23)
template< class InputIter, class Allocator > flat_map( std::sorted_unique_t s, InputIter first, InputIter last,           const key_compare& comp, const Allocator& alloc );	(21)	(since C++23)
template< class InputIter, class Allocator > flat_map( std::sorted_unique_t s, InputIter first, InputIter last,           const Allocator& alloc );	(22)	(since C++23)
flat_map( std::initializer_list<value_type> init,           const key_compare& comp = key_compare() )     : flat_map(init.begin(), init.end(), comp) { }	(23)	(since C++23)
template< class Allocator > flat_map( std::initializer_list<value_type> init, const key_compare& comp,           const Allocator& alloc );	(24)	(since C++23)
template< class Allocator > flat_map( std::initializer_list<value_type> init, const Allocator& alloc );	(25)	(since C++23)
flat_map( std::sorted_unique_t s, std::initializer_list<value_type> init,           const key_compare& comp = key_compare() )     : flat_map(s, init.begin(), init.end(), comp) { }	(26)	(since C++23)
template< class Allocator > flat_map( std::sorted_unique_t s, std::initializer_list<value_type> init,           const key_compare& comp, const Allocator& alloc );	(27)	(since C++23)
template< class Allocator > flat_map( std::sorted_unique_t s, std::initializer_list<value_type> init,           const Allocator& alloc );	(28)	(since C++23)

Constructs new container adaptor from a variety of data sources and optionally using user supplied comparison function object comp and/or allocator alloc.

1) A default constructor. Constructs an empty container adaptor.

2) A copy constructor. Constructs c with the copy of the contents of other.c and compare with other.compare. See allocator usage note below.

3) A move constructor. Constructs the container adaptor with the contents of other using move semantics. See allocator usage note below.

4) First, initializes c.keys with std::move(key_cont), c.values with std::move(mapped_cont), and compare with comp. Then sorts the underlying range [begin(), end()) with respect to value_comp(). Finally, erases the duplicate elements as if by:
auto zv = views::zip(c.keys, c.values);
auto it = ranges::unique(zv, key_equiv(compare)).begin();
auto dist = distance(zv.begin(), it);
c.keys.erase(c.keys.begin() + dist, c.keys.end());
c.values.erase(c.values.begin() + dist, c.values.end());.

5) Same as (4), equivalent to flat_map(key_cont, mapped_cont);. See allocator usage note below.

6) Same as (4), equivalent to flat_map(key_cont, mapped_cont, comp);. See allocator usage note below.

7) Initializes c.keys with std::move(key_cont), c.values with std::move(mapped_cont), and compare with comp.

8) Same as (7), equivalent to flat_map(s, key_cont, mapped_cont);. See allocator usage note below.

9) Same as (7), equivalent to flat_map(s, key_cont, mapped_cont, comp);. See allocator usage note below.

10) Constructs an empty container adaptor.

11,12) Constructs an empty container adaptor. See allocator usage note below.

13) Constructs the container adaptor with the contents of the range [first, last), equivalent to insert(first, last);.

14,15) Same as (13). See allocator usage note below.

16) Constructs the container adaptor with the contents of the range rg. First, uses (10) as delegating constructor. Then initializes c with the contents of rg as if by insert_range(std::forward<R>(rg));.

17) Same as (16) using it as delegating constructor.

18,19) Same as (16). See allocator usage note below.

20) Constructs the underlying containers with the contents of the range [first, last) as if by insert(first, last).

21,22) Same as (20). See allocator usage note below.

23) An initializer-list constructor. Constructs the underlying container with the contents of the initializer list init, using (13) as delegating constructor.

24,25) Same as (23). See allocator usage note below.

26) An initializer-list constructor. Constructs the underlying container with the contents of the initializer list init, using (20) as delegating constructor.

27,28) Save as (26). See allocator usage note below.

Note for overloads (13-15,20-22): If [first, last) is not a valid range, the behavior is undefined.

Note for overloads (4-6,13-19,23-25): If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844).

Allocator usage note

The constructors (2,3,5,6,8,9,11,12,14,15,17,19,21,22,24,25,27,28) are equivalent to the corresponding non-allocator constructors except that the underlying containers c.keys and c.values are constructed with uses-allocator construction. These overloads participate in overload resolution only if std::uses_allocator_v<container_type, Allocator> is true.

Parameters

key_cont	-	a container to be used as source to initialize the underlying keys container
mapped_cont	-	a container to be used as source to initialize the underlying values container
other	-	another flat_map to be used as source to initialize the elements of the underlying containers with
alloc	-	an allocator to use for all memory allocations of the underlying containers
comp	-	a function object to be used for all comparisons of keys
first, last	-	a range to copy the elements from
init	-	an initializer list to initialize the elements of the underlying containers with
rg	-	a container compatible range (that is, an input_range whose elements are convertible to value_type) to be used as source to initialize the underlying containers
fr	-	a disambiguation tag that indicates that the contained member should be range constructed
s	-	a disambiguation tag that indicates that the input sequence is sorted with respect to value_comp() and all its elements are unique
Type requirements
- InputIt must meet the requirements of LegacyInputIterator.
- Compare must meet the requirements of Compare.
- Allocator must meet the requirements of Allocator.

Complexity

1) Constant.

2) Linear in size of other.

3) Same as the corresponding move-constructor of the wrapped container, i.e. constant or linear in size of cont.

4-6) Linear in \(\scriptsize N\)N if cont is sorted with respect to value_comp(), otherwise \(\scriptsize \mathcal{O}(N\cdot\log{(N)})\)𝓞(N·log(N)), where \(\scriptsize N\)N is the value of key_cont.size() before this call.

7-9) Same as the corresponding move-constructor of the wrapped container, i.e. constant or linear in size of cont.

10-12) Constant.

13-15) Linear in \(\scriptsize N\)N if the input range [first, last) is sorted with respect to value_comp(), otherwise \(\scriptsize \mathcal{O}(N\cdot\log{(N)})\)𝓞(N·log(N)), where \(\scriptsize N\)N is the value of key_cont.size() before this call.

16-19) Linear in \(\scriptsize N\)N if the input range rg is sorted with respect to value_comp(), otherwise \(\scriptsize \mathcal{O}(N\cdot\log{(N)})\)𝓞(N·log(N)), where \(\scriptsize N\)N is the value of key_cont.size() before this call.

20-22) Linear in size of [first, last).

23-25) Linear in \(\scriptsize N\)N if the elements of init are sorted with respect to value_comp(), otherwise \(\scriptsize \mathcal{O}(N\cdot\log{(N)})\)𝓞(N·log(N)), where \(\scriptsize N\)N is the value of key_cont.size() before this call.

26-28) Linear in size of init.

Exceptions

Calls to Allocator::allocate may throw.

Notes

After container move construction (overload (3)), references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in *this. The current standard makes this guarantee via the blanket statement in [container.reqmts]/67, and a more direct guarantee is under consideration via LWG issue 2321.

See also

operator=

assigns values to the container adaptor (public member function)