23 Containers library [containers]

23.5 Unordered associative containers [unord]

23.5.4 Class template unordered_map [unord.map]

23.5.4.2 unordered_map 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());

1

Effects: Constructs an empty unordered_map using the specified hash function, key equality function, 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.

2

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());

3

Effects: Constructs an empty unordered_map using the specified hash function, key equality function, 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). max_load_factor() returns 1.0.

4

Complexity: Average case linear, worst case quadratic.