std::unordered_map::unordered_map
STD:无序[医]地图::无序[医]地图
| (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) |
从各种数据源构造新容器。可选地使用所提供的用户bucket_count
作为要创建的最少数量的桶,hash
作为散列函数,equal
作为比较键和alloc
作为分配器。
1%29构造空容器。集max_load_factor()
到1.0。对于默认构造函数,桶的数量是实现定义的。
2%29构造包含范围内容的容器。[first, last)
.成套max_load_factor()
如果范围中的多个元素具有比较等价的键,则未指定插入了%28挂起的元素LWG2844%29
3%29复制构造函数。的内容的副本构造容器。other,复制加载因子、谓词和哈希函数。如果alloc不提供,则通过调用std::allocator_traits<allocator_type>::select_on_container_copy_construction(other.get_allocator())...
4%29移动构造函数。的内容构造容器。other
使用移动语义。如果alloc
如果不提供分配器,则通过移动构造从属于other
...
5%29使用初始化程序列表的内容构造容器。init
,和无序一样[医]映射%28 init
.start%28%29,init
.end%28%29%29。
参数
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 |
类型要求
-输入必须符合输入器的要求。
复杂性
1%29常数
2%29平均情况下线性最坏情况二次之间的距离first
和last
3%29线性other
4%29常数。如果alloc
被赋予和alloc != other.get_allocator()
,然后是线性的。
5%29平均线性最坏情况二次型init
注记
在容器移动构造%28重载%284%29%29之后,引用、指针和迭代器%28---other
保持有效,但引用当前在*this
.现行标准通过第23.2.1节中的总括声明作出这一保证。集装箱。所需经费/12,目前正在考虑通过以下方式提供更直接的担保:lwg 2321...
例
二次
#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;
}
};
struct Foo {
Foo(int val_) : val(val_) {}
int val;
bool operator==(const Foo &rhs) const { return val == rhs.val; }
};
namespace std {
template<> struct hash<Foo> {
std::size_t operator()(const Foo &f) const {
return std::hash<int>{}(f.val
}
};
}
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()
//Option 1 for a constructor with a custom Key type
// Define the KeyHash and KeyEqual structs and use them in the template
std::unordered_map<Key, std::string, KeyHash, KeyEqual> m6 = {
{ {"John", "Doe"}, "example"},
{ {"Mary", "Sue"}, "another"}
};
//Option 2 for a constructor with a custom Key type
// Define a const == operator for the class/struct and specialize std::hash
// structure in the std namespace
std::unordered_map<Foo, std::string> m7 = {
{ Foo(1), "One"}, { 2, "Two"}, { 3, "Three"}
};
//Option 3: Use lambdas
// Note that the initial bucket count has to be passed to the constructor
struct Goo {int val; };
auto hash = [](const Goo &g){ return std::hash<int>{}(g.val };
auto comp = [](const Goo &l, const Goo &r){ return l.val == r.val; };
std::unordered_map<Goo, double, decltype(hash), decltype(comp)> m8(10, hash, comp
}
二次
另见
operator= | assigns values to the container (public member function) |
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