std::multimap<Key,T,Compare,Allocator>::emplace
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Containers library
(C++17)
(C++11)
(C++26)
(C++26)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++23)
(C++23)
(C++23)
(C++23)
(C++20)
(C++23)
Tables
std::multimap
(C++11)
(C++11)
(C++11)
(C++17)
(C++23)
multimap::emplace
(C++11)
(C++11)
(C++17)
(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)
Deduction guides (C++17)
template< class... Args >
iterator emplace( Args&&... args );
(since C++11) iterator emplace( Args&&... args );
(constexpr since C++26)
Inserts a new element into the container constructed in-place with the given args.
The constructor of the new element (i.e. std::pair <const Key, T>) is called with exactly the same arguments as supplied to emplace, forwarded via std::forward <Args>(args)....
If value_type is not EmplaceConstructible into multimap from args, the behavior is undefined.
No iterators or references are invalidated.
[edit] Parameters
args
-
arguments to forward to the constructor of the element
[edit] Return value
An iterator to the inserted element.
[edit] Exceptions
If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).
[edit] Complexity
Logarithmic in the size of the container.
[edit] Notes
Careful use of emplace allows the new element to be constructed while avoiding unnecessary copy or move operations.
[edit] Example
Run this code
#include <iostream> #include <string> #include <utility> #include <map> int main() { std::multimap <std::string, std::string > m; // uses pair's move constructor m.emplace(std::make_pair (std::string ("a"), std::string ("a"))); // uses pair's converting move constructor m.emplace(std::make_pair ("b", "abcd")); // uses pair's template constructor m.emplace("d", "ddd"); // emplace with duplicate key m.emplace("d", "DDD"); // uses pair's piecewise constructor m.emplace(std::piecewise_construct, std::forward_as_tuple ("c"), std::forward_as_tuple (10, 'c')); for (const auto& p : m) std::cout << p.first << " => " << p.second << '\n'; }
Output:
a => a b => abcd c => cccccccccc d => ddd d => DDD