prepare for c++17

code/4/4.1.cpp

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+//
+// 4.1.cpp
+// c++1x tutorial
+//
+// created by changkun at shiyanlou.com
+//
+// std::array
+
+#include <iostream>
+#include <array>
+
+void foo(int *p, int len) {
+    for (int i = 0; i != len; ++i) {
+        std::cout << p[i] << std::endl;
+    }
+}
+
+int main() {
+    std::array<int, 4> arr= {1,4,3,2};
+    
+    //int len = 4;
+    //std::array<int, len> arr = {1,2,3,4}; // 非法, 数组大小参数必须是常量表达式
+    
+    // C 风格接口传参
+    // foo(arr, arr.size());           // 非法, 无法隐式转换
+    foo(&arr[0], arr.size());
+    foo(arr.data(), arr.size());
+    
+    // 更多接口使用
+    std::sort(arr.begin(), arr.end());
+    for(auto &i : arr)
+        std::cout << i << std::endl;
+    
+    return 0;
+}

code/4/4.2.cpp

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+//
+// 4.2.cpp
+// c++1x tutorial
+//
+// created by changkun at shiyanlou.com
+//
+// 无序容器
+
+#include <iostream>
+#include <string>
+#include <unordered_map>
+#include <map>
+
+int main() {
+    // 两组结构按同样的顺序初始化
+    std::unordered_map<int, std::string> u = {
+        {1, "1"},
+        {3, "3"},
+        {2, "2"}
+    };
+    std::map<int, std::string> v = {
+        {1, "1"},
+        {3, "3"},
+        {2, "2"}
+    };
+    
+    // 分别对两组结构进行遍历
+    std::cout << "std::unordered_map" << std::endl;
+    for( const auto & n : u)
+        std::cout << "Key:[" << n.first << "] Value:[" << n.second << "]\n";
+    
+    std::cout << std::endl;
+    std::cout << "std::map" << std::endl;
+    for( const auto & n : v)
+        std::cout << "Key:[" << n.first << "] Value:[" << n.second << "]\n";
+}

code/4/4.3.cpp

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+//
+// 4.3.cpp
+// c++1x tutorial
+//
+// created by changkun at shiyanlou.com
+//
+// std::tuple 及其操作
+
+
+#include <tuple>
+#include <iostream>
+#include <boost/variant.hpp>
+
+auto get_student(int id)
+{
+    if (id == 0)
+        return std::make_tuple(3.8, 'A', "张三");
+    if (id == 1)
+        return std::make_tuple(2.9, 'C', "李四");
+    if (id == 2)
+        return std::make_tuple(1.7, 'D', "王五");
+    // 返回类型被推断为 std::tuple<double, char, std::string>
+    return std::make_tuple(0.0, 'D', "null");
+}
+
+template <size_t n, typename... T>
+boost::variant<T...> _tuple_index(size_t i, const std::tuple<T...>& tpl) {
+    if (i == n)
+        return std::get<n>(tpl);
+    else if (n == sizeof...(T) - 1)
+        throw std::out_of_range("越界.");
+    else
+        return _tuple_index<(n < sizeof...(T)-1 ? n+1 : 0)>(i, tpl);
+}
+template <typename... T>
+boost::variant<T...> tuple_index(size_t i, const std::tuple<T...>& tpl) {
+    return _tuple_index<0>(i, tpl);
+}
+
+template <typename T>
+auto tuple_len(T &tpl) {
+    return std::tuple_size<T>::value;
+}
+
+int main()
+{
+    auto student = get_student(0);
+    std::cout << "ID: 0, "
+    << "GPA: " << std::get<0>(student) << ", "
+    << "成绩: " << std::get<1>(student) << ", "
+    << "姓名: " << std::get<2>(student) << '\n';
+    
+    double gpa;
+    char grade;
+    std::string name;
+    
+    // 元组进行拆包
+    std::tie(gpa, grade, name) = get_student(1);
+    std::cout << "ID: 1, "
+    << "GPA: " << gpa << ", "
+    << "成绩: " << grade << ", "
+    << "姓名: " << name << '\n';
+    
+    
+    std::tuple<std::string, double, double, int> t("123", 4.5, 6.7, 8);
+    std::cout << std::get<std::string>(t) << std::endl;
+    // std::cout << std::get<double>(t) << std::endl;   // 非法, 引发编译期错误
+    std::cout << std::get<3>(t) << std::endl;
+    
+    // 拼接元组
+    auto new_tuple = std::tuple_cat(get_student(1), std::move(t));
+    
+    // 迭代
+    for(int i = 0; i != tuple_len(new_tuple); ++i)
+        // 运行期索引
+        std::cout << tuple_index(i, new_tuple) << std::endl;
+}