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

 

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

 

template< class M > std::pair<iterator, bool> insert_or_assign( const key_type& k, M&& obj );	(1)	(since C++23)
template< class M > std::pair<iterator, bool> insert_or_assign( key_type&& k, M&& obj );	(2)	(since C++23)
template< class K, class M > std::pair<iterator, bool> insert_or_assign( K&& k, M&& obj );	(3)	(since C++23)
template< class M > iterator insert_or_assign( const_iterator hint, const key_type& k, M&& obj );	(4)	(since C++23)
template< class M > iterator insert_or_assign( const_iterator hint, key_type&& k, M&& obj );	(5)	(since C++23)
template< class K, class M > iterator insert_or_assign( const_iterator hint, K&& k, M&& obj );	(6)	(since C++23)

1,2) If a key equivalent to k already exists in the container, assigns std::forward<M>(obj) to the mapped_type corresponding to the key k. If the key does not exist, inserts the new value as if by

• (1,2) try_emplace(std::forward<decltype(k)>(k), std::forward<M>(obj)),
• (4,5) try_emplace(hint, std::forward<decltype(k)>(k), std::forward<M>(obj)).

The program is ill-formed if either std::is_assignable_v<mapped_type&, M> or std::is_constructible_v<mapped_type, M> is false.

3,6) If a key equivalent to k already exists in the container, assigns std::forward<M>(obj) to the mapped_type corresponding to the key k. Otherwise, equivalent to

• (3) try_emplace(std::forward<K>(k), std::forward<M>(obj)),
• (6) try_emplace(hint, std::forward<K>(k), std::forward<M>(obj)).

The conversion from k into key_type must construct an object u, for which find(k) == find(u) is true. Otherwise, the behavior is undefined.

These overloads participate in overload resolution only if :

• The qualified-id Compare::is_transparent is valid and denotes a type.
• std::is_constructible_v<key_type, K> is true.
• std::is_assignable_v<mapped_type&, M> is true.
• std::is_constructible_v<mapped_type, M> is true.

Parameters

k	-	the key used both to look up and to insert if not found
hint	-	iterator to the position before which the new element will be inserted
obj	-	the value to insert or assign

Return value

1-3) The bool component is true if the insertion took place and false if the assignment took place. The iterator component is pointing at the element that was inserted or updated.

4-6) Iterator pointing at the element that was inserted or updated.

Complexity

1-3) Same as for emplace.

4-6) Same as for emplace_hint.

Notes

insert_or_assign returns more information than operator[] and does not require default-constructibility of the mapped type.

Example

Run this code

#include <flat_map>
#include <iostream>
#include <string>
 
void print_node(const auto& node)
{
    std::cout << '[' << node.first << "] = " << node.second << '\n';
}
 
void print_result(auto const& pair)
{
    std::cout << (pair.second ? "inserted: " : "assigned: ");
    print_node(*pair.first);
}
 
int main()
{
    std::flat_map<std::string, std::string> map;
 
    print_result(map.insert_or_assign("a", "apple"));
    print_result(map.insert_or_assign("b", "banana"));
    print_result(map.insert_or_assign("c", "cherry"));
    print_result(map.insert_or_assign("c", "clementine"));
 
    for (const auto& node : map)
        print_node(node);
}

Output:

inserted: [a] = apple
inserted: [b] = banana
inserted: [c] = cherry
assigned: [c] = clementine
[a] = apple
[b] = banana
[c] = clementine

See also

operator[]	access or insert specified element (public member function)
at	access specified element with bounds checking (public member function)
insert	inserts elements (public member function)
emplace	constructs element in-place (public member function)
try_emplace	inserts in-place if the key does not exist, does nothing if the key exists (public member function)