public member function
<unordered_set>
template <class... Args> iterator emplace ( Args&&... args );
Construct and insert element
Inserts a new element in the unordered_multiset. This new element is constructed in place using args as the arguments for the element's constructor.
This effectively increases the container size by one.
A similar member function exists, insert, which either copies or moves existing objects into the container.
Parameters
- args
- Arguments passed to the constructor of the a new element to be inserted.
Return value
An iterator to the newly inserted element.
Member type iterator is a forward iterator type.
All iterators in an unordered_multiset have const access to the elements: Elements can be inserted or removed, but not modified while in the container.
The storage for the new element is allocated using allocator_traits<allocator_type>::construct(), which may throw exceptions on failure (for the default allocator, bad_alloc is thrown if the allocation request does not succeed).
Example
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// unordered_multiset::emplace
#include <iostream>
#include <string>
#include <unordered_set>
int main ()
{
std::unordered_multiset<std::string> myums;
myums.emplace ("milk");
myums.emplace ("tea");
myums.emplace ("coffee");
myums.emplace ("milk");
std::cout << "myums contains:";
for (const std::string& x: myums) std::cout << " " << x;
std::cout << std::endl;
return 0;
}
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Possible output:
myset contains: tea coffee milk milk
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Complexity
Average case: constant.
Worst case: linear in container size.
May trigger a rehash (not included).
Iterator validity
On most cases, all iterators in the container remain valid after the insertion. The only exception being when the growth of the container forces a rehash. In this case, all iterators in the container are invalidated.
A rehash is forced if the new container size after the insertion operation would increase above its capacity threshold (calculated as the container's bucket_count multiplied by its max_load_factor).
References to elements in the unordered_multiset container remain valid in all cases, even after a rehash.