anduin / Funny CPP

#include <iostream> #include <vector> #include <array> #include <string> #include <algorithm> #include <ranges> #include <utility> // 1. 正常人类 (C++98) void print_evens_c98(int arr[], int size) { for (int i = 0; i < size; i++) { if (arr[i] % 2 == 0) { std::cout << arr[i] << " "; } } } // 2. 稍微不正常 (C++11) void print_evens_c11(const std::vector<int>& nums) { std::for_each(nums.begin(), nums.end(), [](int n) { if (n % 2 == 0) { std::cout << n << " "; } }); } // 3. 再不正常一点 (C++20) void print_evens_c20(const std::vector<int>& nums) { for (int n : nums | std::views::filter([](int n) { return n % 2 == 0; })) { std::cout << n << " "; } } // 4. 特别不正常 (C++20 纯编译期) template <size_t... Is> constexpr auto get_even_numbers_string_helper(const std::array<int, sizeof...(Is)>& arr, std::index_sequence<Is...>) { auto filter_and_convert = [&](auto index) constexpr { if (arr[index] % 2 == 0) { // Returns an empty string literal to avoid runtime heap allocation return std::to_string(arr[index]) + " "; } return std::string(""); }; return (filter_and_convert(Is) + ...); } template <size_t N> void print_even_in_array(const std::array<int, N>& arr) { std::cout << get_even_numbers_string_helper(arr, std::make_index_sequence<N>{}); } int main() { int arr[] = {5, 2, 8, 1, 6}; std::vector<int> nums_vec = {5, 2, 8, 1, 6}; constexpr std::array<int, 5> nums_arr_constexpr = {5, 2, 8, 1, 6}; std::cout << "1. 正常人类 (C++98):" << std::endl; print_evens_c98(arr, 5); std::cout << "\n\n"; std::cout << "2. 稍微不正常 (C++11):" << std::endl; print_evens_c11(nums_vec); std::cout << "\n\n"; std::cout << "3. 再不正常一点 (C++20):" << std::endl; print_evens_c20(nums_vec); std::cout << "\n\n"; std::cout << "4. 特别不正常 (C++20 纯编译期):" << std::endl; print_even_in_array(nums_arr_constexpr); std::cout << "\n"; return 0; }