{"id":1019,"date":"2020-05-08T17:26:40","date_gmt":"2020-05-08T09:26:40","guid":{"rendered":"https:\/\/beijian99.top\/?p=1019"},"modified":"2025-05-10T09:08:04","modified_gmt":"2025-05-10T01:08:04","slug":"c17-%e6%96%b0%e7%89%b9%e6%80%a7","status":"publish","type":"post","link":"https:\/\/beijian99.top\/?p=1019","title":{"rendered":"C++17 \u65b0\u7279\u6027"},"content":{"rendered":"\n
\"\"<\/figure>\n\n\n\n

\u4e00\u3001C++17 \u53d1\u5e03\u65f6\u95f4<\/p>\n\n\n\n

C++17 \u6807\u51c6\u6b63\u5f0f\u53d1\u5e03\u65f6\u95f4\u4e3a 2017\u5e7412\u6708\uff0cISO \u6807\u51c6\u7f16\u53f7\u4e3a ISO\/IEC 14882:2017\u3002<\/p>\n\n\n\n

\u4e8c\u3001C++17 \u6838\u5fc3\u65b0\u7279\u6027<\/p>\n\n\n\n

    \n
  1. \u7ed3\u6784\u5316\u7ed1\u5b9a (Structured Bindings)<\/li>\n<\/ol>\n\n\n\n
    #include <tuple>
    #include <map>

    \/\/ \u5143\u7ec4\u89e3\u5305
    auto [x, y, z] = std::make_tuple(1, 2.5, \"hello\");

    \/\/ map \u904d\u5386
    std::map<int, std::string> m = {{1, \"one\"}, {2, \"two\"}};
    for (const auto& [key, value] : m) {
        std::cout << key << \": \" << value << '\\n';
    }

    \/\/ \u7ed3\u6784\u4f53\u6210\u5458\u7ed1\u5b9a
    struct Point { int x; int y; };
    Point p{10, 20};
    auto [px, py] = p;<\/code><\/pre>\n\n\n\n
      \n
    1. if<\/code>\/switch<\/code> \u521d\u59cb\u5316\u8bed\u53e5<\/li>\n<\/ol>\n\n\n\n
      \/\/ if \u521d\u59cb\u5316
      if (auto it = m.find(1); it != m.end()) {
          std::cout << \"Found: \" << it->second << '\\n';
      }

      \/\/ switch \u521d\u59cb\u5316
      switch (int n = rand() % 3; n) {
          case 0: \/*...*\/ break;
          case 1: \/*...*\/ break;
          case 2: \/*...*\/ break;
      }<\/code><\/pre>\n\n\n\n
        \n
      1. \u5185\u8054\u53d8\u91cf (Inline Variables)<\/li>\n<\/ol>\n\n\n\n
        \/\/ \u5934\u6587\u4ef6\u4e2d\u5b9a\u4e49\u5185\u8054\u53d8\u91cf\uff08\u907f\u514d\u591a\u91cd\u5b9a\u4e49\u9519\u8bef\uff09
        inline int global_counter = 0;

        \/\/ \u7c7b\u9759\u6001\u6210\u5458\u521d\u59cb\u5316
        class MyClass {
            inline static int count = 0; \/\/ C++17 \u76f4\u63a5\u521d\u59cb\u5316
        };<\/code><\/pre>\n\n\n\n
          \n
        1. \u6298\u53e0\u8868\u8fbe\u5f0f (Fold Expressions)<\/li>\n<\/ol>\n\n\n\n
          template<typename... Args>
          auto sum(Args... args) {
              return (... + args); \/\/ \u4e00\u5143\u53f3\u6298\u53e0
          }

          template<typename... Args>
          void print(Args... args) {
              (std::cout << ... << args) << '\\n'; \/\/ \u4e8c\u5143\u5de6\u6298\u53e0
          }

          \/\/ \u4f7f\u7528
          int total = sum(1, 2, 3, 4, 5); \/\/ 15
          print(\"Hello\", \" \", \"World\");   \/\/ Hello World<\/code><\/pre>\n\n\n\n
            \n
          1. std::optional<\/code><\/li>\n<\/ol>\n\n\n\n
            #include <optional>

            std::optional<int> find(int key) {
                if (key > 0) return key * 2;
                return std::nullopt; \/\/ \u65e0\u503c
            }

            \/\/ \u4f7f\u7528
            if (auto val = find(5)) {
                std::cout << *val << '\\n'; \/\/ 10
            }

            \/\/ \u63d0\u4f9b\u9ed8\u8ba4\u503c
            int result = find(-1).value_or(0); \/\/ 0<\/code><\/pre>\n\n\n\n
              \n
            1. std::variant<\/code><\/li>\n<\/ol>\n\n\n\n
              #include <variant>
              #include <string>

              std::variant<int, double, std::string> v;
              v = 42; \/\/ \u5b58\u50a8 int
              v = 3.14; \/\/ \u5b58\u50a8 double
              v = \"hello\"; \/\/ \u5b58\u50a8 string

              \/\/ \u8bbf\u95ee
              std::visit([](auto&& arg) {
                  std::cout << arg << '\\n';
              }, v);<\/code><\/pre>\n\n\n\n
                \n
              1. std::any<\/code><\/li>\n<\/ol>\n\n\n\n
                #include <any>

                std::any a = 42;
                a = std::string(\"hello\");

                \/\/ \u7c7b\u578b\u5b89\u5168\u8bbf\u95ee
                try {
                    std::string s = std::any_cast<std::string>(a);
                } catch (const std::bad_any_cast& e) {
                    std::cerr << e.what() << '\\n';
                }<\/code><\/pre>\n\n\n\n
                  \n
                1. \u6587\u4ef6\u7cfb\u7edf\u5e93 (std::filesystem<\/code>)<\/li>\n<\/ol>\n\n\n\n
                  #include <filesystem>
                  namespace fs = std::filesystem;

                  \/\/ \u904d\u5386\u76ee\u5f55
                  for (auto& p : fs::directory_iterator(\".\")) {
                      std::cout << p.path() << '\\n';
                  }

                  \/\/ \u6587\u4ef6\u64cd\u4f5c
                  if (fs::exists(\"test.txt\")) {
                      auto size = fs::file_size(\"test.txt\");
                      fs::rename(\"test.txt\", \"new.txt\");
                  }<\/code><\/pre>\n\n\n\n
                    \n
                  1. \u5e76\u884c\u7b97\u6cd5<\/li>\n<\/ol>\n\n\n\n
                    #include <algorithm>
                    #include <execution>
                    #include <vector>

                    std::vector<int> v(1000000);

                    \/\/ \u5e76\u884c\u6392\u5e8f
                    std::sort(std::execution::par, v.begin(), v.end());

                    \/\/ \u5e76\u884c\u67e5\u627e
                    auto it = std::find_if(std::execution::par, 
                                          v.begin(), v.end(), 
                                          [](int x) { return x > 100; });<\/code><\/pre>\n\n\n\n
                      \n
                    1. constexpr if<\/code> (\u7f16\u8bd1\u671f if)<\/li>\n<\/ol>\n\n\n\n
                      template<typename T>
                      auto get_value(T t) {
                          if constexpr (std::is_pointer_v<T>) {
                              return *t; \/\/ \u89e3\u5f15\u7528\u6307\u9488
                          } else {
                              return t; \/\/ \u76f4\u63a5\u8fd4\u56de\u503c
                          }
                      }

                      \/\/ \u4f7f\u7528
                      int x = 10;
                      int* p = &x;
                      auto v1 = get_value(x); \/\/ 10
                      auto v2 = get_value(p); \/\/ 10<\/code><\/pre>\n\n\n\n
                        \n
                      1. \u7c7b\u6a21\u677f\u53c2\u6570\u63a8\u5bfc (Class Template Argument Deduction)<\/li>\n<\/ol>\n\n\n\n
                        std::pair p(1, 2.5); \/\/ \u81ea\u52a8\u63a8\u5bfc\u4e3a std::pair<int, double>
                        std::vector v{1, 2, 3}; \/\/ \u81ea\u52a8\u63a8\u5bfc\u4e3a std::vector<int>

                        \/\/ \u81ea\u5b9a\u4e49\u7c7b\u63a8\u5bfc\u6307\u5357
                        template<typename T>
                        struct MyContainer {
                            MyContainer(T t) : value(t) {}
                            T value;
                        };

                        \/\/ \u63a8\u5bfc\u6307\u5357
                        MyContainer(const char*) -> MyContainer<std::string>;

                        MyContainer c(\"hello\"); \/\/ \u63a8\u5bfc\u4e3a MyContainer<std::string><\/code><\/pre>\n\n\n\n
                          \n
                        1. std::string_view<\/code><\/li>\n<\/ol>\n\n\n\n
                          #include <string_view>

                          void process(std::string_view sv) {
                              \/\/ \u4e0d\u62e5\u6709\u6570\u636e\uff0c\u907f\u514d\u62f7\u8d1d
                              std::cout << sv.substr(0, 5) << '\\n';
                          }

                          \/\/ \u4f7f\u7528
                          process(\"Hello World\"); \/\/ \u4e0d\u62f7\u8d1d\u5b57\u7b26\u4e32
                          process(std::string(\"C++17\")); \/\/ \u4ecestd::string\u8f6c\u6362<\/code><\/pre>\n\n\n\n
                            \n
                          1. \u5d4c\u5957\u547d\u540d\u7a7a\u95f4\u5b9a\u4e49<\/li>\n<\/ol>\n\n\n\n
                            \/\/ C++11\/14 \u65b9\u5f0f
                            namespace A {
                                namespace B {
                                    namespace C {
                                        \/*...*\/
                                    }
                                }
                            }

                            \/\/ C++17 \u7b80\u5316\u65b9\u5f0f
                            namespace A::B::C {
                                \/*...*\/
                            }<\/code><\/pre>\n\n\n\n
                              \n
                            1. [[maybe_unused]]<\/code> \u5c5e\u6027<\/li>\n<\/ol>\n\n\n\n
                              void foo(int x, [[maybe_unused]] int y) {
                                  \/\/ \u53ef\u80fd\u4e0d\u4f7f\u7528\u53c2\u6570y\uff0c\u907f\u514d\u7f16\u8bd1\u5668\u8b66\u544a
                                  std::cout << x << '\\n';
                              }<\/code><\/pre>\n\n\n\n
                                \n
                              1. std::byte<\/code><\/li>\n<\/ol>\n\n\n\n
                                #include <cstddef>

                                std::byte b{0x7F};
                                std::byte mask{0xF0};
                                auto result = b & mask; \/\/ \u4f4d\u64cd\u4f5c<\/code><\/pre>\n\n\n\n
                                \u4e09\u3001C++17 \u91cd\u8981\u6539\u8fdb\u603b\u7ed3<\/p>\n\n\n\n
                                \u7c7b\u522b<\/th>\u4e3b\u8981\u7279\u6027<\/th><\/tr><\/thead>
                                \u8bed\u6cd5\u589e\u5f3a<\/td>\u7ed3\u6784\u5316\u7ed1\u5b9a\u3001if\/switch\u521d\u59cb\u5316\u3001\u6298\u53e0\u8868\u8fbe\u5f0f\u3001constexpr if<\/td><\/tr>
                                \u7c7b\u578b\u7cfb\u7edf<\/td>std::optional\u3001std::variant\u3001std::any\u3001std::string_view<\/td><\/tr>
                                \u5e93\u6269\u5c55<\/td>\u6587\u4ef6\u7cfb\u7edf\u3001\u5e76\u884c\u7b97\u6cd5\u3001std::byte\u3001\u6570\u5b66\u7279\u6b8a\u51fd\u6570<\/td><\/tr>
                                \u6a21\u677f\u6539\u8fdb<\/td>\u7c7b\u6a21\u677f\u53c2\u6570\u63a8\u5bfc\u3001auto\u975e\u7c7b\u578b\u6a21\u677f\u53c2\u6570<\/td><\/tr>
                                \u5176\u4ed6<\/td>\u5185\u8054\u53d8\u91cf\u3001\u5d4c\u5957\u547d\u540d\u7a7a\u95f4\u3001\u5c5e\u6027\u589e\u5f3a<\/td><\/tr><\/tbody><\/table><\/figure>\n","protected":false},"excerpt":{"rendered":"
                                \u4e00\u3001C++17 \u53d1\u5e03\u65f6\u95f4 C++17 \u6807\u51c6\u6b63\u5f0f\u53d1\u5e03\u65f6\u95f4\u4e3a 2017\u5e7412\u6708\uff0cISO \u6807\u51c6\u7f16\u53f7\u4e3a ISO\/IEC […]<\/p>\n","protected":false},"author":1,"featured_media":1021,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[153],"tags":[154],"class_list":["post-1019","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-cpp","tag-cpp"],"_links":{"self":[{"href":"https:\/\/beijian99.top\/index.php?rest_route=\/wp\/v2\/posts\/1019","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/beijian99.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/beijian99.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/beijian99.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/beijian99.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1019"}],"version-history":[{"count":2,"href":"https:\/\/beijian99.top\/index.php?rest_route=\/wp\/v2\/posts\/1019\/revisions"}],"predecessor-version":[{"id":1022,"href":"https:\/\/beijian99.top\/index.php?rest_route=\/wp\/v2\/posts\/1019\/revisions\/1022"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/beijian99.top\/index.php?rest_route=\/wp\/v2\/media\/1021"}],"wp:attachment":[{"href":"https:\/\/beijian99.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1019"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/beijian99.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1019"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/beijian99.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1019"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}