26 Containers library [containers]

26.5 Unordered associative containers [unord]

26.5.4 Class template unordered_­map [unord.map]

26.5.4.2 Constructors [unord.map.cnstr]

unordered_map() : unordered_map(size_type(see below)) { } explicit unordered_map(size_type n, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type());
Effects: Constructs an empty unordered_­map using the specified hash function, key equality predicate, and allocator, and using at least n buckets.
For the default constructor, the number of buckets is implementation-defined.
max_­load_­factor() returns 1.0.
Complexity: Constant.
template<class InputIterator> unordered_map(InputIterator f, InputIterator l, size_type n = see below, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); unordered_map(initializer_list<value_type> il, size_type n = see below, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type());
Effects: Constructs an empty unordered_­map using the specified hash function, key equality predicate, and allocator, and using at least n buckets.
If n is not provided, the number of buckets is implementation-defined.
Then inserts elements from the range [f, l) for the first form, or from the range [il.begin(), il.end()) for the second form.
max_­load_­factor() returns 1.0.
Complexity: Average case linear, worst case quadratic.