C迭代器模式与算法迭代器是STL中连接容器和算法的桥梁。通过统一的迭代器接口算法可以独立于容器实现。理解迭代器的分类和用法对于高效使用STL至关重要。迭代器分为输入、输出、前向、双向和随机访问五种类别。#include#include#include#include#include#includetemplateclass SimpleVector {T* data_;size_t size_;size_t capacity_;public:class Iterator {T* ptr_;public:using iterator_category std::random_access_iterator_tag;using value_type T;using difference_type std::ptrdiff_t;using pointer T*;using reference T;explicit Iterator(T* ptr) : ptr_(ptr) {}reference operator*() const { return *ptr_; }pointer operator-() const { return ptr_; }Iterator operator() { ptr_; return *this; }Iterator operator(int) { Iterator tmp(*this); ptr_; return tmp; }Iterator operator--() { --ptr_; return *this; }Iterator operator--(int) { Iterator tmp(*this); --ptr_; return tmp; }Iterator operator(difference_type n) { ptr_ n; return *this; }Iterator operator-(difference_type n) { ptr_ - n; return *this; }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_; }reference operator[](difference_type n) const { return ptr_[n]; }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_; }};SimpleVector() : data_(nullptr), size_(0), capacity_(0) {}void push_back(const T value) {if (size_ capacity_) {size_t new_cap capacity_ 0 ? 1 : capacity_ * 2;T* new_data new T[new_cap];for (size_t i 0; i size_; i) new_data[i] data_[i];delete[] data_;data_ new_data;capacity_ new_cap;}data_[size_] value;}Iterator begin() { return Iterator(data_); }Iterator end() { return Iterator(data_ size_); }size_t size() const { return size_; }};void random_access_iterator_demo() {SimpleVector vec;for (int i 0; i 10; i) vec.push_back(i);for (auto it vec.begin(); it ! vec.end(); it) {std::cout *it ;}std::cout \n;std::sort(vec.begin(), vec.end(), std::greater());for (const auto v : vec) std::cout v ;std::cout \n;}反向迭代器从后向前遍历。void reverse_iterator_demo() {std::vector vec {1, 2, 3, 4, 5};std::cout Forward: ;for (auto it vec.begin(); it ! vec.end(); it)std::cout *it ;std::cout \nReverse: ;for (auto it vec.rbegin(); it ! vec.rend(); it)std::cout *it ;std::cout \n;}流迭代器操作输入输出流。void stream_iterator_demo() {std::istringstream iss(10 20 30 40 50);std::vector nums;std::copy(std::istream_iterator(iss),std::istream_iterator(),std::back_inserter(nums));std::ostream_iterator out(std::cout, );std::copy(nums.begin(), nums.end(), out);std::cout \n;}插入迭代器自动插入元素。void insert_iterator_demo() {std::vector source {1, 2, 3, 4, 5};std::vector dest;std::copy(source.begin(), source.end(), std::back_inserter(dest));std::list lst;std::copy(source.begin(), source.end(), std::front_inserter(lst));std::set set;std::copy(source.begin(), source.end(), std::inserter(set, set.end()));std::cout dest: ;for (int n : dest) std::cout n ;std::cout \nlst: ;for (int n : lst) std::cout n ;std::cout \n;}迭代器适配器修改行为。void iterator_adapters() {std::vector data {1, 2, 3, 4, 5};std::vector dest;std::transform(data.begin(), data.end(), std::back_inserter(dest),[](int n) { return n * 2; });auto it std::find(data.begin(), data.end(), 3);auto dist std::distance(data.begin(), it);std::cout Found 3 at distance: dist \n;std::advance(it, 2);std::cout After advance: *it \n;}自定义迭代器实现范围。class Range {int start_, end_, step_;public:class Iterator {int current_, step_;public:using iterator_category std::forward_iterator_tag;using value_type int;using difference_type int;Iterator(int cur, int step) : current_(cur), step_(step) {}int operator*() const { return current_; }Iterator operator() { current_ step_; return *this; }bool operator!(const Iterator other) const { return current_ ! other.current_; }};Range(int end) : start_(0), end_(end), step_(1) {}Range(int start, int end, int step 1) : start_(start), end_(end), step_(step) {}Iterator begin() const { return Iterator(start_, step_); }Iterator end() const { return Iterator(end_, step_); }};void range_iterator_demo() {std::cout Range(0, 10): ;for (int i : Range(0, 10)) std::cout i ;std::cout \n;std::cout Range(0, 20, 2): ;for (int i : Range(0, 20, 2)) std::cout i ;std::cout \n;}迭代器类别标签用于算法优化。templatevoid advance_impl(Iterator it, int n, std::random_access_iterator_tag) {it n;std::cout Random access advance\n;}templatevoid advance_impl(Iterator it, int n, std::bidirectional_iterator_tag) {for (int i 0; i n; i) it;std::cout Bidirectional advance\n;}void iterator_category_demo() {std::vector vec {1, 2, 3};auto vit vec.begin();advance_impl(vit, 2, std::random_access_iterator_tag{});std::list lst {1, 2, 3};auto lit lst.begin();advance_impl(lit, 2, std::bidirectional_iterator_tag{});}迭代器是C泛型编程的基石理解迭代器有助于编写通用高效的算法。
