NAME¶

std::multiset::emplace - std::multiset::emplace

Synopsis¶

template< class... Args > (since C++11)
iterator emplace( Args&&... args );

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

The constructor of the new element is called with exactly the same arguments as
supplied to emplace, forwarded via std::forward<Args>(args)....

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

No iterators or references are invalidated.

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¶

Logarithmic in the size of the container.

Example¶

// Run this code

#include <chrono>
#include <cstddef>
#include <functional>
#include <iomanip>
#include <iostream>
#include <string>
#include <set>

class Dew
{
private:
int a, b, c;

public:
Dew(int _a, int _b, int _c)
: a(_a), b(_b), c(_c)
{}

bool operator<(const Dew& other) const
{
return (a < other.a) ||
(a == other.a && b < other.b) ||
(a == other.a && b == other.b && c < other.c);
}
};

constexpr int nof_operations{101};

std::size_t set_emplace()
{
std::multiset<Dew> set;
for (int i = 0; i < nof_operations; ++i)
for (int j = 0; j < nof_operations; ++j)
for (int k = 0; k < nof_operations; ++k)
set.emplace(i, j, k);

return set.size();
}

std::size_t set_insert()
{
std::multiset<Dew> set;
for (int i = 0; i < nof_operations; ++i)
for (int j = 0; j < nof_operations; ++j)
for (int k = 0; k < nof_operations; ++k)
set.insert(Dew(i, j, k));

return set.size();
}

void time_it(std::function<int()> set_test, std::string what = "")
{
const auto start = std::chrono::system_clock::now();
const auto the_size = set_test();
const auto stop = std::chrono::system_clock::now();
const std::chrono::duration<double, std::milli> time = stop - start;
if (!what.empty() && the_size)
std::cout << std::fixed << std::setprecision(2)
<< time << " for " << what << '\n';
}

int main()
{
time_it(set_insert, "cache warming...");
time_it(set_insert, "insert");
time_it(set_insert, "insert");
time_it(set_emplace, "emplace");
time_it(set_emplace, "emplace");
}

Possible output:¶

499.61ms for cache warming...
447.89ms for insert
436.77ms for insert
430.62ms for emplace
428.61ms for emplace

See also¶

emplace_hint constructs elements in-place using a hint
(C++11) (public member function)
inserts elements
insert or nodes
(since C++17)
(public member function)