C++范围for循环 基于迭代器的语法糖

std::vector<int>

#include <vector>
#include <iostream>

// ...

std::vector<int> numbers = {1, 2, 3, 4, 5};
for (std::vector<int>::iterator it = numbers.begin(); it != numbers.end(); ++it) {
    std::cout << *it << " ";
}
std::cout << std::endl;

#include <vector>
#include <iostream>

// ...

std::vector<int> numbers = {1, 2, 3, 4, 5};
for (int num : numbers) { // 或者更推荐的 const auto&amp;amp; num : numbers
    std::cout << num << " ";
}
std::cout << std::endl;

for (int num : numbers)

numbers

begin()

end()

begin()

end()

begin()

end()

#include <iostream>
#include <stdexcept> // for std::out_of_range

template <typename T>
class MyDynamicArray {
private:
    T* data;
    size_t current_size;
    size_t capacity;

public:
    // 构造函数、析构函数、拷贝构造、赋值运算符省略...

    MyDynamicArray(size_t initial_capacity = 10) : current_size(0), capacity(initial_capacity) {
        data = new T[capacity];
    }

    ~MyDynamicArray() {
        delete[] data;
    }

    void push_back(const T& value) {
        if (current_size == capacity) {
            // 扩容逻辑，这里简化
            std::cout << "扩容中..." << std::endl;
            // 实际中会分配新内存，拷贝旧数据，释放旧内存
            capacity *= 2; // 简单翻倍
            T* new_data = new T[capacity];
            for (size_t i = 0; i < current_size; ++i) {
                new_data[i] = data[i];
            }
            delete[] data;
            data = new_data;
        }
        data[current_size++] = value;
    }

    size_t size() const { return current_size; }

    // 关键：实现迭代器
    class Iterator {
    private:
        T* ptr;
    public:
        using difference_type = std::ptrdiff_t;
        using value_type = T;
        using pointer = T*;
        using reference = T&;
        using iterator_category = std::random_access_iterator_tag; // 或者 forward_iterator_tag

        Iterator(T* p = nullptr) : ptr(p) {}

        // 迭代器核心操作
        reference operator*() const { return *ptr; }
        pointer operator->() const { return ptr; }
        Iterator& operator++() { ++ptr; return *this; } // 前置递增
        Iterator operator++(int) { Iterator temp = *this; ++ptr; return temp; } // 后置递增
        bool operator==(const Iterator& other) const { return ptr == other.ptr; }
        bool operator!=(const Iterator& other) const { return ptr != other.ptr; }
        // 随机访问迭代器还需要更多操作，这里简化
    };

    // 提供 begin() 和 end() 方法
    Iterator begin() { return Iterator(data); }
    Iterator end() { return Iterator(data + current_size); }

    // 为了 const correctness，也提供 const 版本的 begin() 和 end()
    // 这样 MyDynamicArray 对象的 const 引用也能被范围for循环
    const Iterator begin() const { return Iterator(data); }
    const Iterator end() const { return Iterator(data + current_size); }
};

// 示例使用
// int main() {
//     MyDynamicArray<int> arr;
//     arr.push_back(10);
//     arr.push_back(20);
//     arr.push_back(30);

//     for (int val : arr) {
//         std::cout << val << " ";
//     }
//     std::cout << std::endl; // 输出：10 20 30
//     return 0;
// }

MyDynamicArray

Iterator

*

++

==

!=

begin()

end()

std::vector

push_back

erase

begin()

end()

std::vector

const auto&

std::views::enumerate

views

views

std::transform

std::copy_if

#include <vector>
#include <iostream>
#include <ranges> // C++20 Ranges库

// ...

std::vector<int> numbers = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

// 使用Ranges库进行过滤和转换，然后用范围for循环遍历结果
for (int num : numbers 
                | std::views::filter([](int n){ return n % 2 == 0; }) // 过滤出偶数
                | std::views::transform([](int n){ return n * 2; })) { // 将偶数乘以2
    std::cout << num << " ";
}
std::cout << std::endl; // 输出：4 8 12 16 20

numbers

std::views::filter

std::views::transform

views