{"id":19025,"date":"2024-03-15T18:02:52","date_gmt":"2024-03-15T18:02:52","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/how-is-container_of-utilized\/"},"modified":"2024-03-21T14:42:51","modified_gmt":"2024-03-21T14:42:51","slug":"how-is-container_of-utilized","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/how-is-container_of-utilized\/","title":{"rendered":"How is container_of utilized?"},"content":{"rendered":"<p>&#8220;container_of is a C language macro used to obtain a pointer to the structure containing a specific member by using a pointer to that member.&#8221;<\/p>\n<p>Here is how to use it:<\/p>\n<pre class=\"post-pre\"><code><span class=\"hljs-meta\">#<span class=\"hljs-keyword\">define<\/span> container_of(ptr, type, member) \\\r\n    ((type *)((char *)(ptr) - offsetof(type, member)))<\/span>\r\n<\/code><\/pre>\n<p>Explanation of parameters:<\/p>\n<ol>\n<li>ptr: pointer to a member of a structure.<\/li>\n<li>type: the type of the structure.<\/li>\n<li>Member: The name of a member within a structure.<\/li>\n<\/ol>\n<p>The container_of macro calculates the offset of a member within a structure using the offsetof macro, then subtracts the offset from the member pointer to obtain a pointer to the structure.<\/p>\n<p>Here is an example of using the container_of macro:<\/p>\n<pre class=\"post-pre\"><code><span class=\"hljs-meta\">#<span class=\"hljs-keyword\">include<\/span> <span class=\"hljs-string\">&lt;stddef.h&gt;<\/span><\/span>\r\n\r\n<span class=\"hljs-class\"><span class=\"hljs-keyword\">struct<\/span> <span class=\"hljs-title\">Person<\/span> {<\/span>\r\n    <span class=\"hljs-type\">char<\/span> name[<span class=\"hljs-number\">20<\/span>];\r\n    <span class=\"hljs-type\">int<\/span> age;\r\n};\r\n\r\n<span class=\"hljs-type\">int<\/span> <span class=\"hljs-title function_\">main<\/span><span class=\"hljs-params\">()<\/span> {\r\n    <span class=\"hljs-class\"><span class=\"hljs-keyword\">struct<\/span> <span class=\"hljs-title\">Person<\/span> <span class=\"hljs-title\">p<\/span> =<\/span> {<span class=\"hljs-string\">\"John Doe\"<\/span>, <span class=\"hljs-number\">25<\/span>};\r\n    <span class=\"hljs-type\">int<\/span> *p_age = &amp;p.age;\r\n\r\n    <span class=\"hljs-class\"><span class=\"hljs-keyword\">struct<\/span> <span class=\"hljs-title\">Person<\/span> *<span class=\"hljs-title\">p_ptr<\/span> =<\/span> container_of(p_age, <span class=\"hljs-keyword\">struct<\/span> Person, age);\r\n\r\n    <span class=\"hljs-built_in\">printf<\/span>(<span class=\"hljs-string\">\"Name: %s\\n\"<\/span>, p_ptr-&gt;name);\r\n    <span class=\"hljs-built_in\">printf<\/span>(<span class=\"hljs-string\">\"Age: %d\\n\"<\/span>, p_ptr-&gt;age);\r\n\r\n    <span class=\"hljs-keyword\">return<\/span> <span class=\"hljs-number\">0<\/span>;\r\n}\r\n<\/code><\/pre>\n<p>Output result:<\/p>\n<pre class=\"post-pre\"><code>Name: John Doe\r\nAge: 25\r\n<\/code><\/pre>\n<p>In the example above, using the container_of macro, we can obtain a pointer to the struct Person containing the member p.age by accessing p_ptr through the pointer p_age, allowing us to access other members of the struct.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>&#8220;container_of is a C language macro used to obtain a pointer to the structure containing a specific member by using a pointer to that member.&#8221; Here is how to use it: #define container_of(ptr, type, member) \\ ((type *)((char *)(ptr) &#8211; offsetof(type, member))) Explanation of parameters: ptr: pointer to a member of a structure. type: the [&hellip;]<\/p>\n","protected":false},"author":12,"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-19025","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v21.5 (Yoast SEO v21.5) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>How is container_of utilized? 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