C++ STL 迭代器使用指南

#include <iostream>
#include <vector>
#include <list>
#include <map>

int main() {
    // 1. 遍历vector
    std::vector<int> numbers = {1, 2, 3, 4, 5};
    std::cout << "Vector elements: ";
    for (auto it = numbers.begin(); it != numbers.end(); ++it) {
        std::cout << *it << " ";
    }
    
    // 2. 遍历list
    std::list<std::string> fruits = {"Apple", "Banana", "Cherry"};
    std::cout << "\nList elements: ";
    for (auto it = fruits.begin(); it != fruits.end(); ++it) {
        std::cout << *it << " ";
    }
    
    // 3. 遍历map
    std::map<int, std::string> students = {
        {101, "Alice"}, 
        {102, "Bob"}, 
        {103, "Charlie"}
    };
    std::cout << "\nMap elements:\n";
    for (auto it = students.begin(); it != students.end(); ++it) {
        std::cout << "ID: " << it->first << ", Name: " << it->second << "\n";
    }
    
    // 4. 使用const迭代器
    std::cout << "\nConst iteration: ";
    for (auto cit = numbers.cbegin(); cit != numbers.cend(); ++cit) {
        // *cit = 10; // 错误，不能修改常量值
        std::cout << *cit << " ";
    }
    
    // 5. 使用reverse迭代器
    std::cout << "\nReverse iteration: ";
    for (auto rit = numbers.rbegin(); rit != numbers.rend(); ++rit) {
        std::cout << *rit << " ";
    }
    
    return 0;
}

#include <iostream>
#include <vector>
#include <list>

int main() {
    std::vector<int> numbers = {1, 2, 3, 4, 5};
    
    // 使用迭代器修改元素
    for (auto it = numbers.begin(); it != numbers.end(); ++it) {
        *it *= 2; // 每个元素乘以2
    }
    
    std::cout << "Modified vector: ";
    for (int n : numbers) std::cout << n << " ";
    
    // 在list中修改元素
    std::list<std::string> words = {"apple", "banana", "cherry"};
    auto word_it = words.begin();
    std::advance(word_it, 1);
    *word_it = "blueberry";
    
    std::cout << "\nModified list: ";
    for (const auto& word : words) std::cout << word << " ";
    
    // 修改map中的值
    std::map<int, std::string> students = {
        {101, "Alice"}, 
        {102, "Bob"}, 
        {103, "Charlie"}
    };
    
    auto it = students.find(102);
    if (it != students.end()) {
        it->second = "Robert"; // 修改值
    }
    
    std::cout << "\nStudents: ";
    for (const auto& s : students) {
        std::cout << "[" << s.first << ": " << s.second << "] ";
    }
    
    return 0;
}

#include <iostream>
#include <vector>
#include <list>

int main() {
    // vector迭代器失效示例
    std::vector<int> vec = {1, 2, 3, 4, 5};
    auto vec_it = vec.begin() + 2;
    std::cout << "Third element: " << *vec_it << "\n";
    
    // 添加元素导致vector重新分配内存
    vec.push_back(6);
    // 此时vec_it可能失效！
    // std::cout << *vec_it << "\n"; // 未定义行为
    
    // 安全做法：重新获取迭代器
    vec_it = vec.begin() + 2;
    std::cout << "New third element: " << *vec_it << "\n";
    
    // list迭代器失效示例
    std::list<int> lst = {10, 20, 30, 40};
    auto lst_it = lst.begin();
    std::advance(lst_it, 2); // 指向30
    
    // 删除元素
    lst.erase(lst_it); // 删除30，lst_it失效
    
    // 安全做法：erase返回下一个有效迭代器
    lst_it = lst.begin();
    std::advance(lst_it, 1);
    lst_it = lst.erase(lst_it); // 删除20，返回指向30的迭代器
    
    std::cout << "List after erasure: ";
    for (int n : lst) std::cout << n << " ";
    
    return 0;
}

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>

int main() {
    std::vector<int> data = {5, 3, 1, 4, 2};
    
    // 1. 排序
    std::sort(data.begin(), data.end());
    
    // 2. 查找元素
    auto it = std::find(data.begin(), data.end(), 3);
    if (it != data.end()) {
        std::cout << "Found 3 at position: " 
                  << std::distance(data.begin(), it) << "\n";
    }
    
    // 3. 复制元素
    std::vector<int> copy;
    std::copy(data.begin(), data.end(), std::back_inserter(copy));
    
    // 4. 转换元素
    std::vector<int> squares;
    std::transform(data.begin(), data.end(), 
                  std::back_inserter(squares),
                  [](int x) { return x * x; });
    
    // 5. 累加
    int sum = std::accumulate(data.begin(), data.end(), 0);
    std::cout << "Sum: " << sum << "\n";
    
    // 6. 输出到控制台
    std::cout << "Squares: ";
    std::copy(squares.begin(), squares.end(), 
             std::ostream_iterator<int>(std::cout, " "));
    
    return 0;
}

#include <iostream>
#include <iterator>

// 简单的整数范围类
class IntRange {
    int start;
    int end;
public:
    IntRange(int s, int e) : start(s), end(e) {}
    
    // 自定义迭代器
    class Iterator {
        int current;
    public:
        using iterator_category = std::input_iterator_tag;
        using value_type = int;
        using difference_type = int;
        using pointer = int*;
        using reference = int&;
        
        Iterator(int c) : current(c) {}
        
        int operator*() const { return current; }
        Iterator& operator++() { ++current; return *this; }
        Iterator operator++(int) { Iterator tmp = *this; ++current; return tmp; }
        
        bool operator==(const Iterator& other) const {
            return current == other.current;
        }
        
        bool operator!=(const Iterator& other) const {
            return !(*this == other);
        }
    };
    
    Iterator begin() const { return Iterator(start); }
    Iterator end() const { return Iterator(end + 1); }
};

int main() {
    IntRange range(5, 10);
    
    std::cout << "Range: ";
    for (int n : range) {
        std::cout << n << " ";
    }
    
    // 使用STL算法
    std::cout << "\nSum: " 
              << std::accumulate(range.begin(), range.end(), 0);
    
    return 0;
}

#include <iostream>
#include <iterator>
#include <vector>
#include <type_traits>
#include <list>

template <typename Iter>
void print_iterator_type() {
    using traits = std::iterator_traits<Iter>;
    
    std::cout << "Iterator category: ";
    if (std::is_same_v<typename traits::iterator_category, 
                       std::random_access_iterator_tag>) {
        std::cout << "Random Access";
    } else if (std::is_same_v<typename traits::iterator_category, 
                             std::bidirectional_iterator_tag>) {
        std::cout << "Bidirectional";
    } else if (std::is_same_v<typename traits::iterator_category, 
                             std::forward_iterator_tag>) {
        std::cout << "Forward";
    } else {
        std::cout << "Other";
    }
    
    std::cout << "\nValue type: " 
              << typeid(typename traits::value_type).name();
    std::cout << "\nDifference type: " 
              << typeid(typename traits::difference_type).name() << "\n\n";
}

int main() {
    std::vector<int> vec;
    std::list<double> lst;
    
    std::cout << "Vector iterator traits:\n";
    print_iterator_type<decltype(vec.begin())>();
    
    std::cout << "List iterator traits:\n";
    print_iterator_type<decltype(lst.begin())>();
    
    return 0;
}

#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>

int main() {
    // 1. 尽量使用auto简化迭代器声明
    std::vector<int> vec = {5, 3, 1, 4, 2};
    auto it = std::find(vec.begin(), vec.end(), 3);
    
    // 2. 使用const迭代器防止意外修改
    auto cit = vec.cbegin();
    // *cit = 10; // 错误，不能修改
    
    // 3. 使用算法代替手动循环
    std::sort(vec.begin(), vec.end());
    
    // 4. 使用迭代器适配器简化操作
    std::vector<int> squares;
    std::transform(vec.begin(), vec.end(), 
                   std::back_inserter(squares),
                   [](int x) { return x * x; });
    
    // 5. 使用移动语义提高效率
    std::vector<std::string> words = {"Hello", "World"};
    std::vector<std::string> words_copy;
    std::move(words.begin(), words.end(), 
              std::back_inserter(words_copy));
    
    // 6. 避免迭代器失效
    for (auto it = vec.begin(); it != vec.end(); ) {
        if (*it % 2 == 0) {
            it = vec.erase(it); // 正确使用erase返回值
        } else {
            ++it;
        }
    }
    
    // 7. 使用标准算法函数
    auto max_it = std::max_element(vec.begin(), vec.end());
    if (max_it != vec.end()) {
        std::cout << "Max value: " << *max_it << "\n";
    }
    
    // 8. 使用范围for循环简化代码
    std::cout << "Final vec: ";
    for (int n : vec) {
        std::cout << n << " ";
    }
    
    return 0;
}