From cppreference.com
template<classM>std::pair<iterator,bool>insert_or_assign(constKey&k,M&&obj); (1) (since C++17)template<classM>std::pair<iterator,bool>insert_or_assign(Key&&k,M&&obj); (2) (since C++17)template<classK,classM>std::pair<iterator,bool>insert_or_assign(K&&k,M&&obj); (3)(since C++26)template<classM>iteratorinsert_or_assign(const_iteratorhint,constKey&k,M&&obj); (4) (since C++17)template<classM>iteratorinsert_or_assign(const_iteratorhint,Key&&k,M&&obj); (5) (since C++17)template<classK,classM>iteratorinsert_or_assign(const_iteratorhint,K&&k,M&&obj); (6)(since C++26)1,4) If a key equivalent to k already exists in the container, assigns std::forward<M>(obj) to the
corresponding to the key k. If the key does not exist, inserts the new value as if by
, constructing it from value_type(k,std::forward<M>(obj)).
2,5) Same as (1,4), except the mapped value is constructed from value_type(std::move(k),std::forward<M>(obj)).
3,6) If a key equivalent to k already exists in the container, assigns std::forward<M>(obj) to the
corresponding to the key k. If the key does not exist, constructs an object u of value_type with std::forward<K>(k),std::forward<M>(obj)), then inserts u into *this. If equal_range(u.first)==equal_range(k) is false, the behavior is undefined. The value_type must be
into map from std::forward<K>(k),std::forward<M>(obj). This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type. It allows calling this function without constructing an instance of Key.
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
1-3) 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
Notes
insert_or_assign returns more information than
[] and does not require default-constructibility of the mapped type.
macro ValueStdFeature
(C++17)
, std::map::insert_or_assign
__cpp_lib_associative_heterogeneous_insertion
(C++26)Heterogeneous overloads for the remaining member functions in
and
associative
. Overloads (
) and (
). Example
Run this code
#include<iostream>#include<string>#include<map>voidprint_node(constauto&node){std::cout<<'['<<node.first<<"] = "<<node.second<<'\n';}voidprint_result(autoconst&pair){std::cout<<(pair.second?"inserted: ":"assigned: ");print_node(*pair.first);}intmain(){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(constauto&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
access or insert specified element
(public member function)
access specified element with bounds checking
(public member function)
inserts elements or nodes(since C++17)
(public member function)
(C++11)
constructs element in-place
(public member function)