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

 

C++

Compiler support

Freestanding and hosted

Language

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

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

Views

span (C++20)

 

std::map

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_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)

 

template <class M> std::pair<iterator, bool> insert_or_assign( const Key& k, M&& obj );	(1)	(since C++17)
template <class M> std::pair<iterator, bool> insert_or_assign( Key&& k, M&& obj );	(2)	(since C++17)
template <class M> iterator insert_or_assign( const_iterator hint, const Key& k, M&& obj );	(3)	(since C++17)
template <class M> iterator insert_or_assign( const_iterator hint, Key&& k, M&& obj );	(4)	(since C++17)

1,3) 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 insert, constructing it from value_type(k, std::forward<M>(obj))

2,4) Same as (1,3), except the mapped value is constructed from value_type(std::move(k), std::forward<M>(obj))

The behavior is undefined (until C++20)The program is ill-formed (since C++20) if std::is_assignable_v<mapped_type&, M&&> is false.

No iterators or references are invalidated.

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

1,2) 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

3,4) Iterator pointing at the element that was inserted or updated

Complexity

1,2) Same as for emplace

3,4) Same as for emplace_hint

Notes

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

Feature-test macro:

__cpp_lib_map_try_emplace

Example

Run this code

#include <iostream>
#include <map>
#include <string>
 
auto print_node = [](const auto &node) {
    std::cout << "[" << node.first << "] = " << node.second << '\n';
};
 
auto print_result = [](auto const &pair) {
    std::cout << (pair.second ? "inserted: " : "assigned: ");
    print_node(*pair.first);
};
 
int main()
{
    std::map<std::string, std::string> myMap;
 
    print_result( myMap.insert_or_assign("a", "apple"     ) );
    print_result( myMap.insert_or_assign("b", "banana"    ) );
    print_result( myMap.insert_or_assign("c", "cherry"    ) );
    print_result( myMap.insert_or_assign("c", "clementine") );
 
    for (const auto &node : myMap) { 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 or nodes (since C++17) (public member function)
emplace (C++11)	constructs element in-place (public member function)