{"id":24170,"date":"2024-03-16T02:42:37","date_gmt":"2024-03-16T02:42:37","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/what-is-the-method-for-declaring-and-defining-extern-in-c\/"},"modified":"2024-03-22T03:03:04","modified_gmt":"2024-03-22T03:03:04","slug":"what-is-the-method-for-declaring-and-defining-extern-in-c","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/what-is-the-method-for-declaring-and-defining-extern-in-c\/","title":{"rendered":"What is the method for declaring and defining extern in C++?"},"content":{"rendered":"

In C++, the extern keyword is used to reference global variables, functions, or objects defined in another file. By using the extern keyword, the compiler is informed that the definition of the variable, function, or object is in a different file rather than the current one.<\/p>\n

There are two ways to declare extern.<\/p>\n

    \n
  1. Declare a variable: Declare a global variable in one file where its definition is in another file. For example:<\/li>\n<\/ol>\n
    extern<\/span> int<\/span> globalVariable; \/\/ \u58f0\u660e\u4e00\u4e2a\u5168\u5c40\u53d8\u91cf\uff0c\u5b9a\u4e49\u5728\u5176\u4ed6\u6587\u4ef6\u4e2d<\/span>\r\n<\/code><\/pre>\n
      \n
    1. Reference a function or object: Declare a function or object in one file, with its definition in another file. For example:<\/li>\n<\/ol>\n
      extern<\/span> void<\/span> function<\/span>()<\/span><\/span>; \/\/ \u58f0\u660e\u4e00\u4e2a\u51fd\u6570\uff0c\u5b9a\u4e49\u5728\u5176\u4ed6\u6587\u4ef6\u4e2d<\/span>\r\n\r\nextern<\/span> MyClass object; \/\/ \u58f0\u660e\u4e00\u4e2a\u5bf9\u8c61\uff0c\u5b9a\u4e49\u5728\u5176\u4ed6\u6587\u4ef6\u4e2d<\/span>\r\n<\/code><\/pre>\n
      The correct way to use the extern declaration is to declare in one file and define in another. For example, if a global variable is declared in one file, it should be defined in another file.<\/p>\n
      \/\/ File1.cpp<\/span>\r\nextern<\/span> int<\/span> globalVariable; \/\/ \u58f0\u660e\u5168\u5c40\u53d8\u91cf<\/span>\r\n\r\n\/\/ File2.cpp<\/span>\r\nint<\/span> globalVariable = 10<\/span>; \/\/ \u5b9a\u4e49\u5168\u5c40\u53d8\u91cf<\/span>\r\n<\/code><\/pre>\n
      Note: The extern keyword simply indicates that the variable, function, or object is defined in another file, and it is not necessary to use the extern keyword for declaration. Sometimes in C++, it is possible to define directly in a file without the need for the extern keyword for declaration. In this case, the compiler will consider the variable, function, or object definition as global.<\/p>\n","protected":false},"excerpt":{"rendered":"
      In C++, the extern keyword is used to reference global variables, functions, or objects defined in another file. By using the extern keyword, the compiler is informed that the definition of the variable, function, or object is in a different file rather than the current one. There are two ways to declare extern. Declare a […]<\/p>\n","protected":false},"author":9,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_import_markdown_pro_load_document_selector":0,"_import_markdown_pro_submit_text_textarea":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-24170","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"\nWhat is the method for declaring and defining extern in C++? - Blog - Silicon Cloud<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.silicloud.com\/blog\/what-is-the-method-for-declaring-and-defining-extern-in-c\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"What is the method for declaring and defining extern in C++?\" \/>\n<meta property=\"og:description\" content=\"In C++, the extern keyword is used to reference global variables, functions, or objects defined in another file. 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