# 标准库头文件 <forward_list>

< cpp‎ | header

此头文件是容器库的一部分。

### 包含
<compare> (C++20) | 三路比较运算符支持
<initializer_list> (C++11) | std::initializer_list 类模板
### 类
forward_list (C++11 起) | 单链表 (类模板)
### 函数
operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20 中移除)(C++20) | 按照字典顺序比较 forward_list 中的值 (函数模板)
std::swap(std::forward_list) (C++11) | 特化 std::swap 算法 (函数模板)
erase(std::forward_list)erase_if(std::forward_list) (C++20) | 擦除所有满足特定判别标准的元素 (函数模板)
##### 范围访问
begin cbegin (C++11)(C++14) | 返回指向容器或数组起始的迭代器 (函数模板)
end cend (C++11)(C++14) | 返回指向容器或数组结尾的迭代器 (函数模板)
rbegin crbegin (C++14) | 返回指向一个容器或数组的逆向迭代器 (函数模板)
rend crend (C++14) | 返回容器或数组的逆向尾迭代器 (函数模板)
size ssize (C++17)(C++20) | 返回容器或数组的大小 (函数模板)
empty (C++17) | 检查容器是否为空 (函数模板)
data (C++17) | 获得指向底层数组的指针 (函数模板)

### 概要

    #include <compare>
    #include <initializer_list>

    namespace std {
      // 类模板 forward_list
      template<class T, class Allocator = allocator<T>> class forward_list;

      template<class T, class Allocator>
        bool operator==(const forward_list<T, Allocator>& x,
                        const forward_list<T, Allocator>& y);
      template<class T, class Allocator>
        /*synth-three-way-result*/<T> operator<=>(const forward_list<T, Allocator>& x,
                                                  const forward_list<T, Allocator>& y);

      template<class T, class Allocator>
        void swap(forward_list<T, Allocator>& x, forward_list<T, Allocator>& y)
          noexcept(noexcept(x.swap(y)));

      template<class T, class Allocator, class U>
        typename forward_list<T, Allocator>::size_type
          erase(forward_list<T, Allocator>& c, const U& value);
      template<class T, class Allocator, class Predicate>
        typename forward_list<T, Allocator>::size_type
          erase_if(forward_list<T, Allocator>& c, Predicate pred);

      namespace pmr {
        template<class T>
          using forward_list = std::forward_list<T, polymorphic_allocator<T>>;
      }
    }

#### 类模板 std::forward_list

    namespace std {
      template<class T, class Allocator = allocator<T>>
      class forward_list {
      public:
        // 类型
        using value_type      = T;
        using allocator_type  = Allocator;
        using pointer         = typename allocator_traits<Allocator>::pointer;
        using const_pointer   = typename allocator_traits<Allocator>::const_pointer;
        using reference       = value_type&;
        using const_reference = const value_type&;
        using size_type       = /* 由实现定义 */;
        using difference_type = /* 由实现定义 */;
        using iterator        = /* 由实现定义 */;
        using const_iterator  = /* 由实现定义 */;

        // 构造/复制/销毁
        forward_list() : forward_list(Allocator()) { }
        explicit forward_list(const Allocator&);
        explicit forward_list(size_type n, const Allocator& = Allocator());
        forward_list(size_type n, const T& value, const Allocator& = Allocator());
        template<class InputIt>
          forward_list(InputIt first, InputIt last, const Allocator& = Allocator());
        forward_list(const forward_list& x);
        forward_list(forward_list&& x);
        forward_list(const forward_list& x, const Allocator&);
        forward_list(forward_list&& x, const Allocator&);
        forward_list(initializer_list<T>, const Allocator& = Allocator());
        ~forward_list();
        forward_list& operator=(const forward_list& x);
        forward_list& operator=(forward_list&& x)
          noexcept(allocator_traits<Allocator>::is_always_equal::value);
        forward_list& operator=(initializer_list<T>);
        template<class InputIt>
          void assign(InputIt first, InputIt last);
        void assign(size_type n, const T& t);
        void assign(initializer_list<T>);
        allocator_type get_allocator() const noexcept;

        // 迭代器
        iterator before_begin() noexcept;
        const_iterator before_begin() const noexcept;
        iterator begin() noexcept;
        const_iterator begin() const noexcept;
        iterator end() noexcept;
        const_iterator end() const noexcept;

        const_iterator cbegin() const noexcept;
        const_iterator cbefore_begin() const noexcept;
        const_iterator cend() const noexcept;

        // 容量
        [[nodiscard]] bool empty() const noexcept;
        size_type max_size() const noexcept;

        // 元素访问
        reference front();
        const_reference front() const;

        // 修改器
        template<class... Args> reference emplace_front(Args&&... args);
        void push_front(const T& x);
        void push_front(T&& x);
        void pop_front();

        template<class... Args>
          iterator emplace_after(const_iterator position, Args&&... args);
        iterator insert_after(const_iterator position, const T& x);
        iterator insert_after(const_iterator position, T&& x);

        iterator insert_after(const_iterator position, size_type n, const T& x);
        template<class InputIt>
          iterator insert_after(const_iterator position, InputIt first, InputIt last);
        iterator insert_after(const_iterator position, initializer_list<T> il);

        iterator erase_after(const_iterator position);
        iterator erase_after(const_iterator position, const_iterator last);
        void swap(forward_list&)
          noexcept(allocator_traits<Allocator>::is_always_equal::value);

        void resize(size_type sz);
        void resize(size_type sz, const value_type& c);
        void clear() noexcept;

        // forward_list 操作
        void splice_after(const_iterator position, forward_list& x);
        void splice_after(const_iterator position, forward_list&& x);
        void splice_after(const_iterator position, forward_list& x, const_iterator i);
        void splice_after(const_iterator position, forward_list&& x, const_iterator i);
        void splice_after(const_iterator position, forward_list& x,
                          const_iterator first, const_iterator last);
        void splice_after(const_iterator position, forward_list&& x,
                          const_iterator first, const_iterator last);

        size_type remove(const T& value);
        template<class Predicate> size_type remove_if(Predicate pred);

        size_type unique();
        template<class BinaryPredicate> size_type unique(BinaryPredicate binary_pred);

        void merge(forward_list& x);
        void merge(forward_list&& x);
        template<class Compare> void merge(forward_list& x, Compare comp);
        template<class Compare> void merge(forward_list&& x, Compare comp);

        void sort();
        template<class Compare> void sort(Compare comp);

        void reverse() noexcept;
      };

      template<class InputIt, class Allocator = allocator</*iter-value-type*/<InputIt>>>
        forward_list(InputIt, InputIt, Allocator = Allocator())
          -> forward_list</*iter-value-type*/<InputIt>, Allocator>;

      // 交换
      template<class T, class Allocator>
        void swap(forward_list<T, Allocator>& x, forward_list<T, Allocator>& y)
          noexcept(noexcept(x.swap(y)));
    }