C++如何实现类的迭代器接口

iterator

const_iterator

*

->

++

==

!=

begin()

end()

MyVector

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 #include <cstddef>     // For std::ptrdiff_t #include <iterator>    // For std::iterator_traits (及其相关概念) #include <stdexcept>   // For std::out_of_range #include <algorithm>   // 用于演示 std::sort, std::for_each  template <typename T> class MyVector { private:     T* data;     size_t current_size;     size_t capacity;      void reallocate(size_t new_capacity) {         // 一个简单的重新分配逻辑，实际中可能更复杂，例如处理异常安全         T* new_data = new T[new_capacity];         for (size_t i = 0; i < current_size; ++i) {             new_data[i] = data[i]; // 浅拷贝，实际应考虑深拷贝或移动语义         }         delete[] data;         data = new_data;         capacity = new_capacity;     }  public:     MyVector() : data(nullptr), current_size(0), capacity(0) {}     MyVector(size_t initial_capacity) : current_size(0), capacity(initial_capacity) {         data = new T[capacity];     }     ~MyVector() {         delete[] data;     }      // 简化版push_back     void push_back(const T& value) {         if (current_size == capacity) {             reallocate(capacity == 0 ? 1 : capacity * 2);         }         data[current_size++] = value;     }      T& operator[](size_t index) {         if (index >= current_size) {             throw std::out_of_range("Index out of bounds");         }         return data[index];     }      const T& operator[](size_t index) const {         if (index >= current_size) {             throw std::out_of_range("Index out of bounds");         }         return data[index];     }      size_t size() const { return current_size; }     bool empty() const { return current_size == 0; }      // --- 迭代器实现 ---     class iterator {     public:         // 定义迭代器特性，这是与STL算法交互的关键         using iterator_category = std::random_access_iterator_tag; // 随机访问迭代器         using value_type = T;         using difference_type = std::ptrdiff_t;         using pointer = T*;         using reference = T&;      private:         pointer ptr; // 迭代器内部通常只存储一个指向元素的指针      public:         // 构造函数         iterator(pointer p = nullptr) : ptr(p) {}          // 解引用操作符：访问当前元素         reference operator*() const { return *ptr; }         pointer operator->() const { return ptr; }          // 前缀递增：++it         iterator& operator++() {             ++ptr;             return *this;         }          // 后缀递增：it++         iterator operator++(int) {             iterator temp = *this; // 保存当前状态             ++ptr;                 // 递增             return temp;           // 返回递增前的状态         }          // 前缀递减：--it (双向迭代器需要)         iterator& operator--() {             --ptr;             return *this;         }          // 后缀递减：it-- (双向迭代器需要)         iterator operator--(int) {             iterator temp = *this;             --ptr;             return temp;         }          // 随机访问操作符 (随机访问迭代器需要)         iterator operator+(difference_type n) const { return iterator(ptr + n); }         iterator operator-(difference_type n) const { return iterator(ptr - n); }         difference_type operator-(const iterator& other) const { return ptr - other.ptr; }          iterator& operator+=(difference_type n) { ptr += n; return *this; }         iterator& operator-=(difference_type n) { ptr -= n; return *this; }          reference operator[](difference_type n) const { return ptr[n]; }          // 比较操作符         bool operator==(const iterator& other) const { return ptr == other.ptr; }         bool operator!=(const iterator& other) const { return ptr != other.ptr; }         bool operator<(const iterator& other) const { return ptr < other.ptr; }         bool operator>(const iterator& other) const { return ptr > other.ptr; }         bool operator<=(const iterator& other) const { return ptr <= other.ptr; }         bool operator>=(const iterator& other) const { return ptr >= other.ptr; }     };      // const_iterator 类似 iterator，但返回 const 引用，不允许修改元素     class const_iterator {     public:         using iterator_category = std::random_access_iterator_tag;         using value_type = T;         using difference_type = std::ptrdiff_t;         using pointer = const T*;         using reference = const T&;      private:         pointer ptr;      public:         const_iterator(pointer p = nullptr) : ptr(p) {}         // 允许从非const迭代器隐式转换，这是为了让const MyVector::begin()返回const_iterator         const_iterator(const iterator& other) : ptr(other.operator->()) {}          reference operator*() const { return *ptr; }         pointer operator->() const { return ptr; }          const_iterator& operator++() { ++ptr; return *this; }         const_iterator operator++(int) { const_iterator temp = *this; ++ptr; return temp; }         const_iterator& operator--() { --ptr; return *this; }         const_iterator operator--(int) { const_iterator temp = *this; --ptr; return temp; }          const_iterator operator+(difference_type n) const { return const_iterator(ptr + n); }         const_iterator operator-(difference_type n) const { return const_iterator(ptr - n); }         difference_type operator-(const const_iterator& other) const { return ptr - other.ptr; }          const_iterator& operator+=(difference_type n) { ptr += n; return *this; }         const_iterator& operator-=(difference_type

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