{"id":10672,"date":"2024-03-14T12:31:10","date_gmt":"2024-03-14T12:31:10","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/what-is-the-usage-of-optional-in-c\/"},"modified":"2025-08-04T02:25:47","modified_gmt":"2025-08-04T02:25:47","slug":"what-is-the-usage-of-optional-in-c","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/what-is-the-usage-of-optional-in-c\/","title":{"rendered":"C++ Optional: Complete Usage Guide"},"content":{"rendered":"

The std::optional class template was introduced in the C++17 standard, it is a generic class template that can be used to wrap a value, indicating that the value may or may not exist.<\/p>\n

Here is how to use std::optional:<\/p>\n

    \n
  1. Create an std::optional object and initialize it:<\/li>\n<\/ol>\n
    std::optional<int<\/span>> opt1; \/\/ \u672a\u521d\u59cb\u5316\uff0c\u503c\u4e0d\u5b58\u5728<\/span>\r\nstd::optional<int<\/span>> opt2 = 42<\/span>; \/\/ \u521d\u59cb\u5316\u4e3a42<\/span>\r\n<\/code><\/pre>\n
      \n
    1. Check if the value exists:<\/li>\n<\/ol>\n
      if<\/span> (opt1.has_value<\/span>()) {\r\n    \/\/ \u503c\u5b58\u5728<\/span>\r\n} else<\/span> {\r\n    \/\/ \u503c\u4e0d\u5b58\u5728<\/span>\r\n}\r\n<\/code><\/pre>\n
        \n
      1. Access value:<\/li>\n<\/ol>\n
        if<\/span> (opt2.has_value<\/span>()) {\r\n    int<\/span> value = opt2.value<\/span>(); \/\/ \u83b7\u53d6\u503c<\/span>\r\n    \/\/ \u6216\u8005<\/span>\r\n    int<\/span> value = *opt2; \/\/ \u901a\u8fc7\u89e3\u5f15\u7528\u83b7\u53d6\u503c<\/span>\r\n}\r\n<\/code><\/pre>\n
          \n
        1. Retrieve value or default value:<\/li>\n<\/ol>\n
          int<\/span> value = opt1.value_or<\/span>(0<\/span>); \/\/ \u5982\u679c\u503c\u5b58\u5728\uff0c\u83b7\u53d6\u503c\uff1b\u5426\u5219\u8fd4\u56de\u9ed8\u8ba4\u503c0<\/span>\r\n<\/code><\/pre>\n
            \n
          1. Reset the value of the optional object:<\/li>\n<\/ol>\n
            opt1.reset<\/span>(); \/\/ \u91cd\u7f6e\u503c\uff0c\u4f7f\u5176\u4e0d\u5b58\u5728<\/span>\r\n<\/code><\/pre>\n
            The use of std::optional can help avoid the possibility of null pointer exceptions when using pointers or references, increasing the safety and readability of the code.<\/p>\n","protected":false},"excerpt":{"rendered":"
            The std::optional class template was introduced in the C++17 standard, it is a generic class template that can be used to wrap a value, indicating that the value may or may not exist. Here is how to use std::optional: Create an std::optional object and initialize it: std::optional<int> opt1; \/\/ \u672a\u521d\u59cb\u5316\uff0c\u503c\u4e0d\u5b58\u5728 std::optional<int> opt2 = 42; \/\/ […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_import_markdown_pro_load_document_selector":0,"_import_markdown_pro_submit_text_textarea":"","footnotes":""},"categories":[1],"tags":[274,13413,13431,299,13412],"class_list":["post-10672","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-c","tag-c17","tag-optional-type","tag-programming","tag-stdoptional"],"yoast_head":"\nC++ Optional: Complete Usage Guide - Blog - Silicon Cloud<\/title>\n<meta name=\"description\" content=\"Learn how to use std::optional in C++17. 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