(1) | ||||
| (since C++11) (until C++14) | |||
| (since C++14) | |||
| (1) | (since C++14) | ||
| (1) | (since C++11) | ||
| (2) | (since C++11) | ||
| (2) | (since C++14) | ||
| (2) | (since C++14) | ||
| (3) | (since C++11) | ||
| (3) | (since C++11) | ||
| (4) | (since C++11) | ||
| (4) | (since C++11) | ||
| (5) | (since C++11) | ||
| (5) | (since C++14) | ||
| (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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | #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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