std::map<Key,T,Compare,Allocator>::insert_or_assign
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Tables
std::map (C++17)
(C++17)
(C++23)
map::insert_or_assign
(C++17)
(C++11)
(C++11)
(C++17)
(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
template< class M >
std::pair <iterator, bool> insert_or_assign( const Key& k, M&& obj );
(1)
(since C++17)
std::pair <iterator, bool> insert_or_assign( const Key& k, M&& obj );
template< class M >
std::pair <iterator, bool> insert_or_assign( Key&& k, M&& obj );
(2)
(since C++17)
std::pair <iterator, bool> insert_or_assign( Key&& k, M&& obj );
template< class K, class M >
std::pair <iterator, bool> insert_or_assign( K&& k, M&& obj );
(3)
(since C++26)
std::pair <iterator, bool> insert_or_assign( K&& k, M&& obj );
template< class M >
iterator insert_or_assign( const_iterator hint, const Key& k, M&& obj );
(4)
(since C++17)
iterator insert_or_assign( const_iterator hint, const Key& k, M&& obj );
template< class M >
iterator insert_or_assign( const_iterator hint, Key&& k, M&& obj );
(5)
(since C++17)
iterator insert_or_assign( const_iterator hint, Key&& k, M&& obj );
template< class K, class M >
iterator insert_or_assign( const_iterator hint, K&& k, M&& obj );
(6)
(since C++26)
iterator insert_or_assign( const_iterator hint, K&& k, M&& obj );
1,4) 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)).2,5) 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
mapped_type 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 EmplaceConstructible into map from std::forward <K>(k), std::forward <M>(obj). This overload participates in overload resolution only if Compare is transparent. 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.
[edit] 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
[edit] 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.
[edit] Complexity
1-3) Same as for
emplace.4-6) Same as for
emplace_hint.[edit] Notes
insert_or_assign returns more information than operator [] and does not require default-constructibility of the mapped type.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_map_try_emplace |
201411L |
(C++17) | std::map::try_emplace , std::map::insert_or_assign
|
__cpp_lib_associative_heterogeneous_insertion |
202311L |
(C++26) | Heterogeneous overloads for the remaining member functions in ordered and unordered associative containers. Overloads (3) and (6). |
[edit] Example
Run this code
#include <iostream> #include <string> #include <map> 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::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