std::flat_set<Key,Compare,KeyContainer>:: emplace_hint
template
<
class
...
Args
>
iterator emplace_hint ( const_iterator hint, Args && ... args ) ; |
(since C++23) | |
Inserts a new element into the container as close as possible to the position just before hint .
The constructors of the key and mapped value are called with exactly the same arguments as supplied to the function, forwarded with std:: forward < Args > ( args ) ... .
Information on iterator invalidation is copied from here |
Parameters
hint | - | iterator to the position before which the new element will be inserted |
args | - | arguments to forward to the constructor of the element |
Return value
An iterator to the inserted element, or to the element that prevented the insertion.
Exceptions
If an exception is thrown for any reason, this function has no effect ( strong exception safety guarantee ).
Complexity
This section is incomplete |
Example
#include <chrono> #include <cstddef> #include <functional> #include <iomanip> #include <iostream> #include <flat_set> const int n_operations = 100'500'0; std::size_t set_emplace() { std::flat_set<int> set; for (int i = 0; i < n_operations; ++i) set.emplace(i); return set.size(); } std::size_t set_emplace_hint() { std::flat_set<int> set; auto it = set.begin(); for (int i = 0; i < n_operations; ++i) { set.emplace_hint(it, i); it = set.end(); } return set.size(); } std::size_t set_emplace_hint_wrong() { std::flat_set<int> set; auto it = set.begin(); for (int i = n_operations; i > 0; --i) { set.emplace_hint(it, i); it = set.end(); } return set.size(); } std::size_t set_emplace_hint_corrected() { std::flat_set<int> set; auto it = set.begin(); for (int i = n_operations; i > 0; --i) { set.emplace_hint(it, i); it = set.begin(); } return set.size(); } std::size_t set_emplace_hint_closest() { std::flat_set<int> set; auto it = set.begin(); for (int i = 0; i < n_operations; ++i) it = set.emplace_hint(it, i); return set.size(); } double time_it(std::function<std::size_t()> set_test, const char* what = nullptr, double ratio = 0.0) { const auto start = std::chrono::system_clock::now(); const std::size_t setsize = set_test(); const auto stop = std::chrono::system_clock::now(); const std::chrono::duration<double, std::milli> time = stop - start; if (what != nullptr && setsize > 0) std::cout << std::setw(8) << time << " for " << what << " (ratio: " << (ratio == 0.0 ? 1.0 : ratio / time.count()) << ")\n"; return time.count(); } int main() { std::cout << std::fixed << std::setprecision(2); time_it(set_emplace); // cache warmup const auto x = time_it(set_emplace, "plain emplace"); time_it(set_emplace_hint, "emplace with correct hint", x); time_it(set_emplace_hint_wrong, "emplace with wrong hint", x); time_it(set_emplace_hint_corrected, "corrected emplace", x); time_it(set_emplace_hint_closest, "emplace using returned iterator", x); }
Possible output:
...TODO...
See also
constructs element in-place
(public member function) |
|
inserts elements
(public member function) |