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The performance of `boost::unordered_flat_map` is much better than that of `boost::unordered_map` or other implementations of `std::unordered_map`. Unlike standard unordered associative containers, which are node-based, the elements of a `boost::unordered_flat_map` are held directly in the bucket array, and insertions into an already occupied bucket are diverted to available buckets in the vicinity of the original position. This type of data layout is known as _open addressing_.
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Class Template unordered_flat_map
类模板 unordered++_++flat++_++map
:idprefix: unordered_flat_map_
:idprefix: unordered_flat_map_
`boost::unordered_flat_map` — An open-addressing unordered associative container that associates unique keys with another value.
`boost::unordered++_++flat++_++map` —— 一种开放寻址的无序关联容器，用于将唯一键与另一个值关联。
The performance of `boost::unordered_flat_map` is much better than that of `boost::unordered_map` or other implementations of `std::unordered_map`. Unlike standard unordered associative containers, which are node-based, the elements of a `boost::unordered_flat_map` are held directly in the bucket array, and insertions into an already occupied bucket are diverted to available buckets in the vicinity of the original position. This type of data layout is known as _open addressing_.
`boost::unordered++_++flat++_++map` 的性能远优于 `boost::unordered++_++map` 或其他 `std::unordered++_++map` 的实现。与基于节点的标准无序关联容器不同， `boost::unordered++_++flat++_++map` 的元素直接存储在桶数组中，且当元素被插入到已被占用的桶时，会将其重定向到原始位置附近的可用桶。这种数据布局类型称为__开放寻址法__。
As a result of its using open addressing, the interface of `boost::unordered_flat_map` deviates in a number of aspects from that of `boost::unordered_map`/`std::unordered_map`:
由于采用开放寻址法， `boost::unordered++_++flat++_++map` 的接口在多个方面与 `boost::unordered++_++map` / `std::unordered++_++map` 不同：
- `value_type` must be move-constructible. - Pointer stability is not kept under rehashing. - `begin()` is not constant-time. - There is no API for bucket handling (except `bucket_count`) or node extraction/insertion. - The maximum load factor of the container is managed internally and can't be set by the user.
- `value++_++type` 必须支持移动构造。 - 在重哈希的过程中，指针稳定性无法保持。 - `begin()` 不是常数时间复杂度操作。 - 未提供用于桶管理（除 `bucket++_++count` 外）或节点提取/插入的 API。 - 容器的最大负载因子由内部管理，用户无法进行设置。
Other than this, `boost::unordered_flat_map` is mostly a drop-in replacement of node-based standard unordered associative containers.
除此之外， `boost::unordered++_++flat++_++map` 基本可完全替代基于节点的标准无序关联容器。
Synopsis
概要
:282
---
---
Description
描述
*Template Parameters*
*模板参数*
_Key_
_键_
`std::pair<const Key, T>` must be https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[EmplaceConstructible^] into the container from any `std::pair` object convertible to it, and it also must be https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.
`std::pair<const key,="" t="">` 必须能从任何可转换为它的 `std::pair` 对象满足对容器的 https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[可原位构造^] 要求，并且还必须满足对容器的 https://en.cppreference.com/w/cpp/named_req/Erasable[可擦除^] 要求。</const>
_T_
_T_
_Hash_
_Hash_
A unary function object type that acts a hash function for a `Key`. It takes a single argument of type `Key` and returns a value of type `std::size_t`.
一个一元函数对象类型，用作 `Key` 的哈希函数。它接受一个 `Key` 类型的参数并返回 `std::size_t` 类型的值。
_Pred_
_Pred_
A binary function object that induces an equivalence relation on values of type `Key`. It takes two arguments of type `Key` and returns a value of type `bool`.
一个二元函数对象，在 `Key` 类型的值上诱导出等价关系。它接受两个 `Key` 类型的参数并返回 `bool` 类型的值。
_Allocator_
_Allocator_
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empty
空
```c++ [[nodiscard]] bool empty() const noexcept; ```
```c++ [[nodiscard]] bool empty() const noexcept; ```
Returns:;; `size() == 0`
返回: `size() == 0`
size
大小
max_size
max++_++size
```c++ size_type max_size() const noexcept; ```
```c++ size_type max_size() const noexcept; ```
Returns:;; `size()` of the largest possible container.
返回：可能的最大容器的 `size()`。
Modifiers
修改器
```c++ template<class... Args> std::pair<iterator, bool> emplace(Args&&... args); ```
```c++ template<class... args=""> std::pair<iterator, bool=""> emplace(Args&amp;&amp;... args); ```</iterator,></class...>
```c++ template<class M> std::pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj); template<class M> std::pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj); template<class K, class M> std::pair<iterator, bool> insert_or_assign(K&& k, M&& obj); ```
```c++ template<class m=""> std::pair<iterator, bool=""> insert_or_assign(const key_type&amp; k, M&amp;&amp; obj); template<class m=""> std::pair<iterator, bool=""> insert_or_assign(key_type&amp;&amp; k, M&amp;&amp; obj); template<class k,="" class="" m=""> std::pair<iterator, bool=""> insert_or_assign(K&amp;&amp; k, M&amp;&amp; obj); ```</iterator,></class></iterator,></class></iterator,></class>
```c++ std::pair<iterator, bool> insert(const value_type& obj); std::pair<iterator, bool> insert(const init_type& obj); ```
```c++ std::pair<iterator, bool=""> insert(const value_type&amp; obj); std::pair<iterator, bool=""> insert(const init_type&amp; obj); ```</iterator,></iterator,>
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, pointers and references, but only if the insert causes the load to be greater than the maximum load. + + A call of the form `insert(x)`, where `x` is equally convertible to both `const value_type&` and `const init_type&`, is not ambiguous and selects the `init_type` overload.
要求：`value_type` 需满足 https://en.cppreference.com/w/cpp/named_req/CopyInsertable[可复制插入^] 要求。返回：若执行了插入，则返回类型中的 `bool` 分量为 `true`。+ +若执行了插入，则迭代器指向新插入的元素；否则指向等价的元素。抛出：若调用 `hasher` 以外的操作抛出异常，则函数无效果。注意：可能使迭代器、指针和引用失效，但仅当插入导致负载大于最大负载时才会发生。+ +形式为 `insert(x)` 的调用（其中 `x` 可同等转换为 `const value_type&amp;` 和 `const init_type&amp;`）不会产生歧义，并且会选择 `init_type` 重载。
Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators pointers and references, but only if the insert causes the load to be greater than the maximum load. + + The `template<class K, class M>` only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.
返回：若执行了插入，则返回类型中的 `bool` 分量为 `true`。+ +若执行了插入，则迭代器指向新插入的元素；否则指向等价的元素。抛出：若调用 `hasher` 以外的操作抛出异常，则函数无效果。注意：可能会导致迭代器、指针和引用失效，但仅当插入操作导致负载因子超过最大负载因子时才会发生。+ +`template<class k,="" class="" m="">` 仅在 `Hash::is_transparent` 和 `Pred::is_transparent` 是有效的成员 typedef 时参与重载决议。库假定 `Hash` 可同时以 `K` 和 `Key` 调用，且 `Pred` 是透明的。这提供了异构查找能力，从而避免构造 `Key` 类型实例的开销。</class>
insert_or_assign with Hint
带提示的 insert++_++or++_++assign
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, pointers and references, but only if the insert causes the load to be greater than the maximum load. + + A call of the form `insert(x)`, where `x` is equally convertible to both `value_type&&` and `init_type&&`, is not ambiguous and selects the `init_type` overload.
要求：`value_type` 需满足 https://en.cppreference.com/w/cpp/named_req/MoveInsertable[可移动插入^] 要求。返回：若执行了插入，则返回类型中的 `bool` 分量为 `true`。+ +若执行了插入，则迭代器指向新插入的元素；否则指向等价的元素。抛出：若调用 `hasher` 以外的操作抛出异常，则函数无效果。注意：可能使迭代器、指针和引用失效，但仅当插入导致负载大于最大负载时才会发生。+ +形式为 `insert(x)` 的调用（其中 `x` 可同等转换为 `value_type&amp;&amp;` 和 `init_type&amp;&amp;`）不会产生歧义，并且会选择 `init_type` 重载。
The performance of `boost::unordered_flat_map` is much better than that of `boost::unordered_map` or other implementations of `std::unordered_map`. Unlike standard unordered associative containers, which are node-based, the elements of a `boost::unordered_flat_map` are held directly in the bucket array, and insertions into an already occupied bucket are diverted to available buckets in the vicinity of the original position. This type of data layout is known as _open addressing_.
`boost::unordered++_++flat++_++map` 的性能远优于 `boost::unordered++_++map` 或其他 `std::unordered++_++map` 的实现。与基于节点的标准无序关联容器不同， `boost::unordered++_++flat++_++map` 的元素直接存储在桶数组中，且当元素被插入到已被占用的桶时，会将其重定向到原始位置附近的可用桶。这种数据布局类型称为__开放寻址法__。
```c++ iterator insert(const_iterator hint, const value_type& obj); iterator insert(const_iterator hint, const init_type& obj); ``` Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.
`iterator insert(const_iterator hint, const value_type&amp; obj); iterator insert(const_iterator hint, const init_type&amp; obj);` 当且仅当容器中没有等价的键时，将 `obj` 插入容器。
- `value_type` must be move-constructible. - Pointer stability is not kept under rehashing. - `begin()` is not constant-time. - There is no API for bucket handling (except `bucket_count`) or node extraction/insertion. - The maximum load factor of the container is managed internally and can't be set by the user.
- `value++_++type` 必须支持移动构造。 - 在重哈希的过程中，指针稳定性无法保持。 - `begin()` 不是常数时间复杂度操作。 - 未提供用于桶管理（除 `bucket++_++count` 外）或节点提取/插入的 API。 - 容器的最大负载因子由内部管理，用户无法进行设置。
The elements of the container are held into an internal _bucket array_. An element is inserted into a bucket determined by its hash code, but if the bucket is already occupied (a _collision_), an available one in the vicinity of the original position is used.
容器的元素存储在内部的__桶数组__中。元素根据其哈希码被插入到对应的桶中，但如果该桶已被占用（即发生__冲突__），则会使用原始位置附近可用的桶。
Erase by Position
通过位置擦除
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, pointers and references, but only if the insert causes the load to be greater than the maximum load. + + A call of the form `insert(hint, x)`, where `x` is equally convertible to both `const value_type&` and `const init_type&`, is not ambiguous and selects the `init_type` overload.
要求：`value_type` 需满足 https://en.cppreference.com/w/cpp/named_req/CopyInsertable[可复制插入^] 要求。返回：若执行了插入，则返回类型中的 `bool` 分量为 `true`。+ +若执行了插入，则迭代器指向新插入的元素；否则指向等价的元素。抛出：若调用 `hasher` 以外的操作抛出异常，则函数无效果。注意：可能使迭代器、指针和引用失效，但仅当插入导致负载大于最大负载时才会发生。+ +形式为 `insert(hint, x)` 的调用（其中 `x` 可同等转换为 `const value_type&amp;` 和 `const init_type&amp;`）不会产生歧义，并且会选择 `init_type` 重载。
Erase the element pointed to by `position`.
擦除由 `position` 指向的元素。
Erase by Key
通过键擦除
The size of the bucket array can be automatically increased by a call to `insert`/`emplace`, or as a result of calling `rehash`/`reserve`. The _load factor_ of the container (number of elements divided by number of buckets) is never greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to allow for higher loads.
桶数组的大小可通过调用 `insert` / `emplace` 自动增加，也可通过调用 `rehash` / `reserve` 来调整。容器的__负载因子__（元素数量与桶数量的比值）始终不会超过 `max++_++load++_++factor()` ，但在小规模数据情况下，实现可能允许更高的负载因子。
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. Returns:;; The `bool` component of the return type is `true` if an insert took place. + + If an insert took place, then the iterator points to the newly inserted element. Otherwise, it points to the element with equivalent key. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Notes:;; Can invalidate iterators, pointers and references, but only if the insert causes the load to be greater than the maximum load. + + A call of the form `insert(hint, x)`, where `x` is equally convertible to both `value_type&&` and `init_type&&`, is not ambiguous and selects the `init_type` overload.
要求：`value_type` 需满足 https://en.cppreference.com/w/cpp/named_req/MoveInsertable[可移动插入^] 要求。返回：若执行了插入，则返回类型中的 `bool` 分量为 `true`。+ +若执行了插入，则迭代器指向新插入的元素；否则指向等价的元素。抛出：若调用 `hasher` 以外的操作抛出异常，则函数无效果。注意：可能使迭代器、指针和引用失效，但仅当插入导致负载大于最大负载时才会发生。+ +形式为 `insert(hint, x)` 的调用（其中 `x` 可同等转换为 `value_type&amp;&amp;` 和 `init_type&amp;&amp;`）不会产生歧义，并且会选择 `init_type` 重载。
If `a == other.get_allocator()`, the elements of `other` are transferred directly to the new container; otherwise, elements are moved-constructed from those of `other`. The hash function and predicate are moved-constructed from `other`, and the allocator is copy-constructed from `a`. If statistics are xref:unordered_flat_map_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` iff `a == other.get_allocator()`, and always calls `other.reset_stats()`.
若 `a == other.get_allocator()`，则 `other` 的元素直接转移到新容器中；否则，将通过移动构造从 `other` 的元素创建新元素。哈希函数和谓词通过移动构造从 `other` 获得，分配器则通过复制构造从 `a` 获得。若统计功能已启用（参见 xref:unordered_flat_map_boost_unordered_enable_stats[相关说明]），则仅当 `a == other.get_allocator()` 时转移 `other` 的内部统计信息，且始终会调用 `other.reset_stats()`。
Move construction from a xref:#concurrent_flat_map[`concurrent_flat_map`]. The internal bucket array of `other` is transferred directly to the new container. The hash function, predicate and allocator are moved-constructed from `other`. If statistics are xref:unordered_flat_map_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` and calls `other.reset_stats()`.
从 xref:#concurrent_flat_map[`concurrent_flat_map`][`concurrent++_++flat++_++map`] 移动构造。 `other` 的内部桶数组直接转移至新容器。哈希函数、谓词和分配器均从 `other` 移动构造。若统计功能 xref:#unordered_flat_map_boost_unordered_enable_stats[已启用] ，则转移 `other` 的内部统计信息，并调用 `other.reset++_++stats()` 。
Erases the elements in the range from `first` to `last`.
擦除从 `first` 到 `last` 范围内的元素。
Returns:;; The iterator following the erased elements - i.e. `last`. Throws:;; Nothing in this implementation (neither the `hasher` nor the `key_equal` objects are called).
返回：指向被擦除元素之后位置的迭代器，即 `last`。抛出：在此实现中不会抛出异常（既不调用 `hasher` 也不调用 `key_equal` 对象）。
swap
交换

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The performance of `boost::unordered_flat_map` is much better than that of `boost::unordered_map` or other implementations of `std::unordered_map`. Unlike standard unordered associative containers, which are node-based, the elements of a `boost::unordered_flat_map` are held directly in the bucket array, and insertions into an already occupied bucket are diverted to available buckets in the vicinity of the original position. This type of data layout is known as _open addressing_.
The performance of `boost::unordered_flat_map` is much better than that of `boost::unordered_map` or other implementations of `std::unordered_map`. Unlike standard unordered associative containers, which are node-based, the elements of a `boost::unordered_flat_map` are held directly in the bucket array, and insertions into an already occupied bucket are diverted to available buckets in the vicinity of the original position. This type of data layout is known as _open addressing_.`boost::unordered++_++flat++_++map` 的性能远优于 `boost::unordered++_++map` 或其他 `std::unordered++_++map` 的实现。与基于节点的标准无序关联容器不同， `boost::unordered++_++flat++_++map` 的元素直接存储在桶数组中，且当元素被插入到已被占用的桶时，会将其重定向到原始位置附近的可用桶。这种数据布局类型称为__开放寻址法__。
06/05/2026
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The performance of `boost::unordered_flat_map` is much better than that of `boost::unordered_map` or other implementations of `std::unordered_map`. Unlike standard unordered associative containers, which are node-based, the elements of a `boost::unordered_flat_map` are held directly in the bucket array, and insertions into an already occupied bucket are diverted to available buckets in the vicinity of the original position. This type of data layout is known as _open addressing_.
The performance of `boost::unordered_flat_map` is much better than that of `boost::unordered_map` or other implementations of `std::unordered_map`. Unlike standard unordered associative containers, which are node-based, the elements of a `boost::unordered_flat_map` are held directly in the bucket array, and insertions into an already occupied bucket are diverted to available buckets in the vicinity of the original position. This type of data layout is known as _open addressing_.
06/05/2026
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Unit identifier
54962
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:8
String age
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Last updated
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doc/modules/ROOT/pages/reference/unordered_flat_map_zh_Hans.adoc, string 4