{"id":14843,"date":"2024-03-15T10:03:43","date_gmt":"2024-03-15T10:03:43","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/what-is-the-usage-of-constexpr-in-c\/"},"modified":"2025-08-06T13:35:20","modified_gmt":"2025-08-06T13:35:20","slug":"what-is-the-usage-of-constexpr-in-c","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/what-is-the-usage-of-constexpr-in-c\/","title":{"rendered":"What is the usage of constexpr in C++?"},"content":{"rendered":"

In C++, the keyword ‘constexpr’ is used to declare that an expression or function is a compile-time constant. It can be used in defining constant expressions, variable declarations, function declarations, and other places.<\/p>\n

The use of the constexpr keyword allows delaying compile-time constant calculations until compile time, thereby improving program performance. Its main uses include the following aspects:<\/p>\n

    \n
  1. Declare a constant expression: using the constexpr keyword, you can declare an expression as a compile-time constant. For example:<\/li>\n<\/ol>\n
    constexpr<\/span> int<\/span> size = 10<\/span>;\r\n<\/code><\/pre>\n
      \n
    1. Defining Constants: You can declare and define a compile-time constant using the constexpr keyword. For example:<\/li>\n<\/ol>\n
      constexpr<\/span> int<\/span> factorial<\/span>(int<\/span> n)<\/span> <\/span>{\r\n    return<\/span> (n <= 1<\/span>) ? 1<\/span> : (n * factorial<\/span>(n - 1<\/span>));\r\n}\r\nconstexpr<\/span> int<\/span> result = factorial<\/span>(5<\/span>); \/\/ \u5728\u7f16\u8bd1\u671f\u95f4\u8ba1\u7b97factorial(5)\u7684\u7ed3\u679c\u5e76\u8d4b\u503c\u7ed9result<\/span>\r\n<\/code><\/pre>\n
        \n
      1. constexpr\u5173\u952e\u5b57\u53ef\u4ee5\u5728\u58f0\u660e\u6570\u7ec4\u5927\u5c0f\u65f6\u4f7f\u7528\uff0c\u4f46\u5fc5\u987b\u786e\u4fdd\u6570\u7ec4\u5927\u5c0f\u662f\u4e00\u4e2a\u7f16\u8bd1\u65f6\u5e38\u91cf\u3002\u4f8b\u5982\uff1a<\/li>\n<\/ol>\n
        constexpr<\/span> int<\/span> size = 5<\/span>;\r\nint<\/span> arr[size]; \/\/ \u53ef\u4ee5\u4f7f\u7528\u7f16\u8bd1\u65f6\u5e38\u91cf\u4f5c\u4e3a\u6570\u7ec4\u5927\u5c0f<\/span>\r\n<\/code><\/pre>\n
          \n
        1. The constexpr keyword can be used for template parameters, requiring them to be compile-time constants. For example:<\/li>\n<\/ol>\n
          template<\/span> <int<\/span> N>\r\nvoid<\/span> printArraySize<\/span>()<\/span> <\/span>{\r\n    int<\/span> arr[N];\r\n    std::cout << \"Array size: \"<\/span> << N << std::endl;\r\n}\r\nconstexpr<\/span> int<\/span> size = 10<\/span>;\r\nprintArraySize<\/span><size>(); \/\/ \u7f16\u8bd1\u65f6\u5c55\u5f00\u6a21\u677f\uff0c\u5e76\u5c06size\u4f5c\u4e3a\u5e38\u91cf\u4f20\u9012\u7ed9\u6a21\u677f\u51fd\u6570<\/span>\r\n<\/code><\/pre>\n
          In general, using the constexpr keyword allows programs to perform more calculations during compilation, improving performance, and in some cases avoiding runtime costs.<\/p>\n","protected":false},"excerpt":{"rendered":"
          In C++, the keyword ‘constexpr’ is used to declare that an expression or function is a compile-time constant. It can be used in defining constant expressions, variable declarations, function declarations, and other places. The use of the constexpr keyword allows delaying compile-time constant calculations until compile time, thereby improving program performance. Its main uses include […]<\/p>\n","protected":false},"author":11,"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":[453,1402,299,1404,1403],"class_list":["post-14843","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-development","tag-guide","tag-programming","tag-technology","tag-tutorial"],"yoast_head":"\nWhat is the usage of constexpr in C++? - Blog - Silicon Cloud<\/title>\n<meta name=\"description\" content=\"Learn about what is the usage of constexpr in c++?. 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