std::multiset<Key,Compare,Allocator>::emplace - cppreference.com (original) (raw)

| template< class... Args >iterator emplace( Args&&... args ); | | (since C++11) (constexpr since C++26) | | ------------------------------------------------------------- | | ------------------------------------- |

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)....

If value_type is not EmplaceConstructible into multiset from args, the behavior is undefined.

No iterators or references are invalidated.

Contents

• 1 Parameters
• 2 Return value
• 3 Exceptions
• 4 Complexity
• 5 Notes
• 6 Example
• 7 See also

[edit] Parameters

[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

#include #include #include #include #include #include #include   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 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 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] |