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std::multiset<Key,Compare,Allocator>::emplace

From cppreference.com
< cpp‎ | container‎ | multiset
 
 
 
 
template< class... Args >
iterator emplace( Args&&... args );
(since C++11)

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

Careful use of emplace allows the new element to be constructed while avoiding unnecessary copy or move operations. The constructor of the new element is called with exactly the same arguments as supplied to emplace, forwarded via std::forward<Args>(args)....

No iterators or references are invalidated.

Contents

[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] Example

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

[edit] See also

constructs elements in-place using a hint
(public member function) [edit]
inserts elements or nodes(since C++17)
(public member function) [edit]