# 标准库头文件 <deque>

< 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
deque | 双端队列 (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 deque 中的值 (函数模板)
std::swap(std::deque) | 特化 std::swap 算法 (函数模板)
erase(std::deque)erase_if(std::deque) (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 deque
      template<class T, class Allocator = allocator<T>> class deque;

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

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

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

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

### 类模板 std::deque

    namespace std {
      template<class T, class Allocator = allocator<T>>
      class deque {
      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 */;
        using reverse_iterator       = std::reverse_iterator<iterator>;
        using const_reverse_iterator = std::reverse_iterator<const_iterator>;

        // 构造/复制/销毁
        deque() : deque(Allocator()) { }
        explicit deque(const Allocator&);
        explicit deque(size_type n, const Allocator& = Allocator());
        deque(size_type n, const T& value, const Allocator& = Allocator());
        template<class InputIt>
          deque(InputIt first, InputIt last, const Allocator& = Allocator());
        deque(const deque& x);
        deque(deque&&);
        deque(const deque&, const Allocator&);
        deque(deque&&, const Allocator&);
        deque(initializer_list<T>, const Allocator& = Allocator());

        ~deque();
        deque& operator=(const deque& x);
        deque& operator=(deque&& x)
          noexcept(allocator_traits<Allocator>::is_always_equal::value);
        deque& 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               begin() noexcept;
        const_iterator         begin() const noexcept;
        iterator               end() noexcept;
        const_iterator         end() const noexcept;
        reverse_iterator       rbegin() noexcept;
        const_reverse_iterator rbegin() const noexcept;
        reverse_iterator       rend() noexcept;
        const_reverse_iterator rend() const noexcept;

        const_iterator         cbegin() const noexcept;
        const_iterator         cend() const noexcept;
        const_reverse_iterator crbegin() const noexcept;
        const_reverse_iterator crend() const noexcept;

        // 容量
        [[nodiscard]] bool empty() const noexcept;
        size_type size() const noexcept;
        size_type max_size() const noexcept;
        void      resize(size_type sz);
        void      resize(size_type sz, const T& c);
        void      shrink_to_fit();

        // 元素访问
        reference       operator[](size_type n);
        const_reference operator[](size_type n) const;
        reference       at(size_type n);
        const_reference at(size_type n) const;
        reference       front();
        const_reference front() const;
        reference       back();
        const_reference back() const;

        // 修改器
        template<class... Args> reference emplace_front(Args&&... args);
        template<class... Args> reference emplace_back(Args&&... args);
        template<class... Args> iterator emplace(const_iterator position, Args&&... args);

        void push_front(const T& x);
        void push_front(T&& x);
        void push_back(const T& x);
        void push_back(T&& x);

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

        void pop_front();
        void pop_back();

        iterator erase(const_iterator position);
        iterator erase(const_iterator first, const_iterator last);
        void     swap(deque&)
          noexcept(allocator_traits<Allocator>::is_always_equal::value);
        void     clear() noexcept;
      };

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

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