(1) | ||
explicit unordered_map( size_type bucket_count = /*implementation-defined*/, const Hash& hash = Hash(), const KeyEqual& equal = KeyEqual(), const Allocator& alloc = Allocator() ); | (since C++11) (until C++14) | |
unordered_map() : unordered_map( size_type(/*implementation-defined*/) {} explicit unordered_map( size_type bucket_count, const Hash& hash = Hash(), const KeyEqual& equal = KeyEqual(), const Allocator& alloc = Allocator() ); | (since C++14) | |
unordered_map( size_type bucket_count, const Allocator& alloc ) : unordered_map(bucket_count, Hash(), KeyEqual(), alloc) {} unordered_map( size_type bucket_count, const Hash& hash, const Allocator& alloc ) : unordered_map(bucket_count, hash, KeyEqual(), alloc) {} | (1) | (since C++14) |
explicit unordered_map( const Allocator& alloc ); | (1) | (since C++11) |
template< class InputIt > unordered_map( InputIt first, InputIt last, size_type bucket_count = /*implementation-defined*/, const Hash& hash = Hash(), const KeyEqual& equal = KeyEqual(), const Allocator& alloc = Allocator() ); | (2) | (since C++11) |
template< class InputIt > unordered_map( InputIt first, InputIt last, size_type bucket_count, const Allocator& alloc ) : unordered_map(first, last, bucket_count, Hash(), KeyEqual(), alloc) {} | (2) | (since C++14) |
template< class InputIt > unordered_map( InputIt first, InputIt last, size_type bucket_count, const Hash& hash, const Allocator& alloc ) : unordered_map(first, last, bucket_count, hash, KeyEqual(), alloc) {} | (2) | (since C++14) |
unordered_map( const unordered_map& other ); | (3) | (since C++11) |
unordered_map( const unordered_map& other, const Allocator& alloc ); | (3) | (since C++11) |
unordered_map( unordered_map&& other ); | (4) | (since C++11) |
unordered_map( unordered_map&& other, const Allocator& alloc ); | (4) | (since C++11) |
unordered_map( std::initializer_list<value_type> init, size_type bucket_count = /*implementation-defined*/, const Hash& hash = Hash(), const KeyEqual& equal = KeyEqual(), const Allocator& alloc = Allocator() ); | (5) | (since C++11) |
unordered_map( std::initializer_list<value_type> init, size_type bucket_count, const Allocator& alloc ) : unordered_map(init, bucket_count, Hash(), KeyEqual(), alloc) {} | (5) | (since C++14) |
unordered_map( std::initializer_list<value_type> init, size_type bucket_count, const Hash& hash, const Allocator& alloc ) : unordered_map(init, bucket_count, hash, KeyEqual(), alloc) {} | (5) | (since C++14) |
Constructs new container from a variety of data sources. Optionally uses user supplied bucket_count
as a minimal number of buckets to create, hash
as the hash function, equal
as the function to compare keys and alloc
as the allocator.
1) Constructs empty container. Sets
max_load_factor()
to 1.0. For the default constructor, the number of buckets is implementation-defined. 2) constructs the container with the contents of the range
[first, last)
. Sets max_load_factor()
to 1.0. 3) copy constructor. Constructs the container with the copy of the contents of
other
, copies the load factor, the predicate, and the hash function as well. If alloc
is not provided, allocator is obtained by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction(other.get_allocator())
. 4) move constructor. Constructs the container with the contents of
other
using move semantics. If alloc
is not provided, allocator is obtained by move-construction from the allocator belonging to other
. 5) constructs the container with the contents of the initializer list
init
, same as unordered_map(init.begin(), init.end()).Parameters
alloc | - | allocator to use for all memory allocations of this container |
bucket_count | - | minimal number of buckets to use on initialization. If it is not specified, implementation-defined default value is used |
hash | - | hash function to use |
equal | - | comparison function to use for all key comparisons of this container |
first, last | - | the range to copy the elements from |
other | - | another container to be used as source to initialize the elements of the container with |
init | - | initializer list to initialize the elements of the container with |
Type requirements | ||
- InputIt must meet the requirements of InputIterator . |
Complexity
1) constant
2) average case linear worst case quadratic in distance between
first
and last
3) linear in size of
other
4) constant. If
alloc
is given and alloc != other.get_allocator()
, then linear. 5) average case linear worst case quadratic in size of
init
Example
#include <unordered_map> #include <vector> #include <bitset> #include <string> #include <utility> struct Key { std::string first; std::string second; }; struct KeyHash { std::size_t operator()(const Key& k) const { return std::hash<std::string>()(k.first) ^ (std::hash<std::string>()(k.second) << 1); } }; struct KeyEqual { bool operator()(const Key& lhs, const Key& rhs) const { return lhs.first == rhs.first && lhs.second == rhs.second; } }; int main() { // default constructor: empty map std::unordered_map<std::string, std::string> m1; // list constructor std::unordered_map<int, std::string> m2 = { {1, "foo"}, {3, "bar"}, {2, "baz"}, }; // copy constructor std::unordered_map<int, std::string> m3 = m2; // move constructor std::unordered_map<int, std::string> m4 = std::move(m2); // range constructor std::vector<std::pair<std::bitset<8>, int>> v = { {0x12, 1}, {0x01,-1} }; std::unordered_map<std::bitset<8>, double> m5(v.begin(), v.end()); // constructor for a custom type std::unordered_map<Key, std::string, KeyHash, KeyEqual> m6 = { { {"John", "Doe"}, "example"}, { {"Mary", "Sue"}, "another"} }; }
See also
operator=
| assigns values to the container (public member function) |
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