NAME¶

std::flat_multimap::emplace - std::flat_multimap::emplace

Synopsis¶

template< class... Args > (since C++23)
iterator emplace( Args&&... args );

Inserts a new element into the container constructed in-place with the given args.

Initializes an object t of type std::pair<key_type, mapped_type> with
std::forward<Args>(args)...; if the map already contains an element whose key is
equivalent to t.first, *this is unchanged. Otherwise, equivalent to:

auto key_it = ranges::upper_bound(c.keys, t.first, compare);
auto value_it = c.values.begin() + std::distance(c.keys.begin(), key_it);
c.keys.insert(key_it, std::move(t.first));
c.values.insert(value_it, std::move(t.second));

This overload participates in overload resolution only if
std::is_constructible_v<std::pair<key_type, mapped_type>, Args...> is true.

Careful use of emplace allows the new element to be constructed while avoiding
unnecessary copy or move operations.

Information on iterator invalidation is copied from here

Parameters¶

args - arguments to forward to the constructor of the element

Return value¶

An iterator to the inserted element.

Exceptions¶

If an exception is thrown for any reason, this function has no effect (strong
exception safety guarantee).

Complexity¶

Linear in the size of the container

Example¶

// Run this code

#include <iostream>
#include <string>
#include <utility>
#include <flat_map>

int main()
{
std::flat_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

See also¶

emplace_hint constructs elements in-place using a hint
(public member function)
inserts in-place if the key does not exist, does nothing if the key
try_emplace exists
(public member function)
insert inserts elements
(public member function)