std::unordered_multimap::emplace
| template< class... Args > iterator emplace( Args&&... args ); |
(since C++11) | |
Inserts a new element to the container. The element is constructed in-place, i.e. no copy or move operations are performed. The constructor of the element type (value_type, that is, std::pair<const Key, T>) is called with exactly the same arguments as supplied to the function, forwarded with std::forward<Args>(args)....
If rehashing occurs due to the insertion, all iterators are invalidated. Otherwise iterators are not affected. References are not invalidated. Rehashing occurs only if the new number of elements is equal to or greater than max_load_factor()*bucket_count().
Contents |
[edit] Parameters
| args | - | arguments to forward to the constructor of the element |
[edit] Return value
Returns an iterator to the inserted element.
[edit] Exceptions
If an exception is thrown by any operation, this function has no effect.
[edit] Complexity
Amortized constant on average, worst case linear in the size of the container.
[edit] Example
#include <iostream> #include <utility> #include <unordered_map> int main() { std::unordered_multimap<std::string, std::string> m; // uses pair's copy-constructor m.emplace(std::make_pair(std::string("a"), std::string("a"))); // uses pair's converting copy constructor m.emplace(std::make_pair("b", "abcd")); // uses pair's template constructor 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'; } }
Possible output:
a => a b => abcd c => cccccccccc d => ddd
[edit] See also
| constructs elements in-place using a hint (public member function) | |
| inserts elements (public member function) | |
