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Traverses the container `c` and removes all elements for which the supplied predicate returns `true`.
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Return `true` if `x.size() == y.size()` and for every element in `x`, there is an element in `y` with the same key, with an equal value (using `operator==` to compare the value types).
如果 `x.size() == y.size()` 并且对于 `x` 中的每个元素，在 `y` 中都有一个具有相同键且值相等的元素（使用 `operator==` 比较值类型），则返回 `true`。
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Notes:;; Behavior is undefined if the two containers don't have equivalent equality predicates.
备注：;; 如果两个容器不具有等价的相等谓词，则行为未定义。
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operator!
operator!
```c++ template<class Key, class T, class Hash, class Pred, class Alloc> bool operator!=(const unordered_map<Key, T, Hash, Pred, Alloc>& x, const unordered_map<Key, T, Hash, Pred, Alloc>& y); ```
```c++ template<class key,="" class="" t,="" hash,="" pred,="" alloc=""> bool operator!=(const unordered_map<key, t,="" hash,="" pred,="" alloc="">&amp; x, const unordered_map<key, t,="" hash,="" pred,="" alloc="">&amp; y); ```</key,></key,></class>
Return `false` if `x.size() == y.size()` and for every element in `x`, there is an element in `y` with the same key, with an equal value (using `operator==` to compare the value types).
如果 `x.size() == y.size()` 并且对于 `x` 中的每个元素，在 `y` 中都有一个具有相同键且值相等的元素（使用 `operator==` 比较值类型），则返回 `false`。
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Notes:;; Behavior is undefined if the two containers don't have equivalent equality predicates.
备注：;; 如果两个容器不具有等价的相等谓词，则行为未定义。
Swap
交换
```c++ template<class Key, class T, class Hash, class Pred, class Alloc> void swap(unordered_map<Key, T, Hash, Pred, Alloc>& x, unordered_map<Key, T, Hash, Pred, Alloc>& y) noexcept(noexcept(x.swap(y))); ```
```c++ template<class key,="" class="" t,="" hash,="" pred,="" alloc=""> void swap(unordered_map<key, t,="" hash,="" pred,="" alloc="">&amp; x, unordered_map<key, t,="" hash,="" pred,="" alloc="">&amp; y) noexcept(noexcept(x.swap(y))); ```</key,></key,></class>
Swaps the contents of `x` and `y`.
交换 `x` 和 `y` 的内容。
:1737
If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is `true` then the containers' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior.
如果 `Allocator::propagate_on_container_swap` 已声明且 `Allocator::propagate_on_container_swap::value` 为 `true`，则交换两个容器的分配器。否则，使用不相等的分配器进行交换将导致未定义行为。
Effects:;; `x.swap(y)` Throws:;; Doesn't throw an exception unless it is thrown by the copy constructor or copy assignment operator of `key_equal` or `hasher`. Notes:;; The exception specifications aren't quite the same as the C++11 standard, as the equality predicate and hash function are swapped using their copy constructors.
效果：;; `x.swap(y)`
抛出：;; 除非由 `key_equal` 或 `hasher` 的复制构造函数或复制赋值运算符抛出异常，否则不会抛出异常。
备注：;; 异常规范与 C++11 标准不完全相同，因为相等谓词和哈希函数是通过它们的复制构造函数进行交换的。
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erase_if
erase_if
```c++ template<class K, class T, class H, class P, class A, class Predicate> typename unordered_map<K, T, H, P, A>::size_type erase_if(unordered_map<K, T, H, P, A>& c, Predicate pred); ```
```c++ template<class k,="" class="" t,="" h,="" p,="" a,="" predicate=""> typename unordered_map<k, t,="" h,="" p,="" a="">::size_type erase_if(unordered_map<k, t,="" h,="" p,="" a="">&amp; c, Predicate pred); ```</k,></k,></class>
Traverses the container `c` and removes all elements for which the supplied predicate returns `true`.
遍历容器 `c` 并移除所有使给定谓词返回 `true` 的元素。
Returns:;; The number of erased elements. Notes:;; Equivalent to: + + ```c++ auto original_size = c.size(); for (auto i = c.begin(), last = c.end(); i != last; ) { if (pred(*i)) { i = c.erase(i); } else { ++i; } } return original_size - c.size(); ``` + Note that the references passed to `pred` are non-const.
返回：;; 被移除的元素数量。备注：;; 等价于：```c++auto original_size = c.size();for (auto i = c.begin(), last = c.end(); i != last; ) { if (pred(*i)) { i = c.erase(i); } else { ++i; }}return original_size - c.size();```注意，传递给 `pred` 的引用是非常量的。
Serialization
序列化
``unordered_map``s can be archived/retrieved by means of link:../../../../../serialization/index.html[Boost.Serialization^] using the API provided by this library. Both regular and XML archives are supported.
`unordered_map` 可以通过本库提供的 API，使用 link:../../../../../serialization/index.html[Boost.Serialization^] 进行归档/恢复。支持常规归档和 XML 归档。
Saving an unordered_map to an archive
将 unordered_map 保存到归档
Saves all the elements of an `unordered_map` `x` to an archive (XML archive) `ar`.
将 `unordered_map` `x` 的所有元素保存到归档（XML 归档）`ar` 中。
Requires:;; `std::remove_const<key_type>::type` and `std::remove_const<mapped_type>::type` are serializable (XML serializable), and they do support Boost.Serialization `save_construct_data`/`load_construct_data` protocol (automatically suported by https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^] types).
要求：;; `std::remove_const<key_type>::type` 和 `std::remove_const<mapped_type>::type` 必须是可序列化的（支持 XML 序列化），并且它们支持 Boost.Serialization 的 `save_construct_data`/`load_construct_data` 协议（该协议由 https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^] 类型的自动支持）。</mapped_type></key_type>
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Loading an unordered_map from an archive
从归档中加载 unordered_map
Deletes all preexisting elements of an `unordered_map` `x` and inserts from an archive (XML archive) `ar` restored copies of the elements of the original `unordered_map` `other` saved to the storage read by `ar`.
删除 `unordered_map` `x` 中所有已存在的元素，并从归档（XML 归档）`ar` 中插入由 `ar` 所读取存储中保存的原始 `unordered_map` `other` 元素的恢复副本。
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[EmplaceConstructible^] from `(std::remove_const<key_type>::type&&, std::remove_const<mapped_type>::type&&)`. `x.key_equal()` is functionally equivalent to `other.key_equal()`. Note:;; If the archive was saved using a release of Boost prior to Boost 1.84, the configuration macro `BOOST_UNORDERED_ENABLE_SERIALIZATION_COMPATIBILITY_V0` has to be globally defined for this operation to succeed; otherwise, an exception is thrown.
要求：;; `value_type` 可以从 `(std::remove_const<key_type>::type&amp;&amp;, std::remove_const<mapped_type>::type&amp;&amp;)` 进行 https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[EmplaceConstructible^]。`x.key_equal()` 在功能上等价于 `other.key_equal()`。
注意：;; 如果归档是使用 Boost 1.84 之前的 Boost 版本保存的，则必须全局定义配置宏 `BOOST_UNORDERED_ENABLE_SERIALIZATION_COMPATIBILITY_V0` 才能使此操作成功；否则将抛出异常。</mapped_type></key_type>
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---
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Saving an iterator/const_iterator to an archive
将迭代器/常量迭代器保存到归档中
Saves the positional information of an `iterator` (`const_iterator`) `it` to an archive (XML archive) `ar`. `it` can be and `end()` iterator.
将 `iterator`（`const_iterator`）`it` 的位置信息保存到归档（XML 归档）`ar` 中。`it` 可以是 `end()` 迭代器。
Requires:;; The `unordered_map` `x` pointed to by `it` has been previously saved to `ar`, and no modifying operations have been issued on `x` between saving of `x` and saving of `it`.
要求：;; `it` 所指向的 `unordered_map` `x` 此前已保存至 `ar`，并且在保存 `x` 和保存 `it` 之间未对 `x` 执行任何修改操作。
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English Chinese (Simplified Han script) Actions
Returns:;; An iterator referring to the first element of the container, or if the container is empty the past-the-end value for the container.
返回：指向容器第一个元素的迭代器，如果容器为空则返回容器的尾后迭代器。
```c++ const_iterator cend() const noexcept; ```
```c++ const_iterator cend() const noexcept; ```
Returns:;; A `const_iterator` which refers to the past-the-end value for the container.
返回：指向容器尾后值的 `const_iterator`。
Size and Capacity
大小与容量
empty
空
```c++ [[nodiscard]] bool empty() const noexcept; ```
```c++ [[nodiscard]] bool empty() const noexcept; ```
Returns:;; `size() == 0`
返回：`size() == 0`。
size
大小
```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
emplace
原地构造
```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++ std::pair<iterator, bool> insert(value_type&& obj); ```
```c++ std::pair<iterator, bool=""> insert(value_type&amp;&amp; obj); ```</iterator,>
```c++ template<class K, class T, class H, class P, class A, class Predicate> typename unordered_map<K, T, H, P, A>::size_type erase_if(unordered_map<K, T, H, P, A>& c, Predicate pred); ```
```c++ template<class k,="" class="" t,="" h,="" p,="" a,="" predicate=""> typename unordered_map<k, t,="" h,="" p,="" a="">::size_type erase_if(unordered_map<k, t,="" h,="" p,="" a="">&amp; c, Predicate pred); ```</k,></k,></class>
Traverses the container `c` and removes all elements for which the supplied predicate returns `true`.
遍历容器 `c` 并移除所有使给定谓词返回 `true` 的元素。
Saving an iterator/const_iterator to an archive
将迭代器/常量迭代器保存到归档中
Saves the positional information of an `iterator` (`const_iterator`) `it` to an archive (XML archive) `ar`. `it` can be and `end()` iterator.
将 `iterator`（`const_iterator`）`it` 的位置信息保存到归档（XML 归档）`ar` 中。`it` 可以是 `end()` 迭代器。
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.
返回：返回类型的 bool 分量为 true 表示发生了插入。
如果发生了插入，则迭代器指向新插入的元素；否则，指向具有等价键的元素。
Copy Insert with Hint
带提示的复制插入
```c++ iterator insert(const_iterator hint, const value_type& obj); ``` Inserts `obj` in the container if and only if there is no element in the container with an equivalent key.
```c++iterator insert(const_iterator hint, const value_type&amp; obj);```
当且仅当容器中没有具有等价键的元素时，才将 `obj` 插入容器。
Returns:;; 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:;; The standard is fairly vague on the meaning of the hint. But the only practical way to use it, and the only way that Boost.Unordered supports is to point to an existing element with the same key. + + Can invalidate iterators, but only if the insert causes the load factor to be greater to or equal to the maximum load factor. + + Pointers and references to elements are never invalidated. + + 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：如果发生了插入，则迭代器指向新插入的元素；否则，指向具有等价键的元素。
抛出：如果除调用 `hasher` 之外的操作抛出异常，则该函数无效果。
注意：标准关于 `hint` 的含义表述相当模糊。但唯一实际的使用方式，也是 Boost.Unordered 支持的唯一方式，是将其指向一个具有相同键的已存在元素。
可能使迭代器失效，但仅当插入导致负载因子大于或等于最大负载因子时才会发生。 指向元素的指针和引用永远不会失效。
`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` 可同时使用 `K` 和 `Key` 调用，且 `Pred` 是透明的。这支持了异构查找，从而避免了实例化 `Key` 类型对象的开销。</class>
Extract by Iterator
通过迭代器提取
Returns:;; 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:;; This function is similiar to xref:#unordered_map_emplace_hint[emplace_hint] except the `value_type` is constructed using: + + -- ```c++
返回：如果发生了插入，则迭代器指向新插入的元素；否则，指向具有等价键的元素。 抛出：如果除调用 `hasher` 之外的操作抛出异常，则该函数无效果。
注意：此函数类似于 xref:#unordered_map_emplace_hint[emplace_hint]，区别在于 `value_type` 的构造方式如下：
```c++
instead of xref:#unordered_map_emplace_hint[emplace_hint] which simply forwards all arguments to ``value_type``'s constructor.
而不是像 xref:#unordered_map_emplace_hint[emplace_hint] 那样简单地将所有参数转发给 `value_type` 的构造函数。
```c++ node_type extract(const_iterator position); ```
```c++ node_type extract(const_iterator position); ```
Removes the element pointed to by `position`.
移除 `position` 所指向的元素。
Returns:;; A `node_type` owning the element. Notes:;; A node extracted using this method can be inserted into a compatible `unordered_multimap`.
返回：一个拥有该元素的 `node_type`。
注意：通过此方法提取的节点可以插入到兼容的 `unordered_multimap` 中。
Extract by Key
通过键提取
```c++ node_type extract(const key_type& k); template<class K> node_type extract(K&& k); ```
```c++ node_type extract(const key_type&amp; k); template<class k=""> node_type extract(K&amp;&amp; k); ```</class>

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Traverses the container `c` and removes all elements for which the supplied predicate returns `true`.
Traverses the container `c` and removes all elements for which the supplied predicate returns遍历容器 `c` 并移除所有使给定谓词返回 `true`. 的元素。
06/05/2026
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Traverses the container `c` and removes all elements for which the supplied predicate returns `true`.
Traverses the container `c` and removes all elements for which the supplied predicate returns `true`.
06/05/2026
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English Chinese (Simplified Han script)
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String information

Flags
safe-html, strict-same
Unit identifier
55853
Source string location
:1753
String age
06/05/2026
Last updated
06/06/2026
Source string age
06/05/2026
Translation file AsciiDoc file
doc/modules/ROOT/pages/reference/unordered_map_zh_Hans.adoc, string 471