{"id":5673,"date":"2019-04-29T19:35:09","date_gmt":"2019-04-29T19:35:09","guid":{"rendered":"https:\/\/www.modernescpp.com\/index.php\/c-20-modules\/"},"modified":"2023-06-26T10:11:17","modified_gmt":"2023-06-26T10:11:17","slug":"c-20-modules","status":"publish","type":"post","link":"https:\/\/www.modernescpp.com\/index.php\/c-20-modules\/","title":{"rendered":"Modules"},"content":{"rendered":"

Modules are one of the five prominent features of C++20. Modules will overcome the restrictions of header files. They promise a lot. For example, the separation of header and source files becomes as obsolete as the preprocessor. Ultimately, we will also have faster build times and an easier way to build packages.<\/p>\n

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 \"graphic<\/p>\n

Explaining modules from the user’s perspective is quite easy, but this will not hold for the implementer’s perspective. My plan for this post is to start with a simple example of modules and add more features as we go.<\/p>\n

<\/span>A First Example<\/span><\/h2>\n

First of all, here is my first math<\/code> module.<\/span><\/p>\n

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\/\/ math.cppm<\/span>\r\n\r\nexport<\/span> module math;\r\n\r\nexport<\/span> int<\/span> add<\/span>(int<\/span> fir, int<\/span> sec){\r\n    return<\/span> fir +<\/span> sec;\r\n} \r\n<\/pre>\n<\/div>\n
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The expression export module math<\/span> is the module declaration. By putting export<\/span> before the function adds,<\/span> add <\/span>is exported and can, therefore, be used by a consumer of my module. <\/p>\n
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\/\/ main.cpp<\/span>\r\n\r\nimport math;\r\n\r\nint<\/span> main<\/span>(){\r\n   \r\n   add(2000<\/span>, 20<\/span>);\r\n   \r\n}\r\n<\/pre>\n<\/div>\n
 <\/p>\n
import math<\/span> imports the module math<\/span> and makes the exported names in main.cpp<\/span> visible. This was the easy part. The challenge started when I compiled the program.<\/p>\n
<\/span>Module Declaration Files<\/span><\/h3>\n
But first, did you notice the strange name of the module: math.cppm<\/span>.<\/p>\n