{"id":13922,"date":"2024-03-15T08:08:48","date_gmt":"2024-03-15T08:08:48","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/what-is-the-purpose-of-c-typeid\/"},"modified":"2025-08-06T01:11:45","modified_gmt":"2025-08-06T01:11:45","slug":"what-is-the-purpose-of-c-typeid","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/what-is-the-purpose-of-c-typeid\/","title":{"rendered":"C++ typeid Explained: Purpose and Usage"},"content":{"rendered":"<p>The typeid in C++ is an operator used to retrieve the type information of an expression. It returns a std::type_info object that contains the type information of the expression, including the name of the type.<\/p>\n<p>The typeid is commonly used with dynamic_cast and std::type_info to identify the actual type of an object at runtime, allowing for polymorphism.<\/p>\n<p>Here is an example of how to use typeid:<\/p>\n<pre class=\"post-pre\"><code><span class=\"hljs-meta\">#<span class=\"hljs-keyword\">include<\/span> <span class=\"hljs-string\">&lt;iostream&gt;<\/span><\/span>\r\n<span class=\"hljs-meta\">#<span class=\"hljs-keyword\">include<\/span> <span class=\"hljs-string\">&lt;typeinfo&gt;<\/span><\/span>\r\n\r\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title class_\">Base<\/span> {\r\n   <span class=\"hljs-function\"><span class=\"hljs-keyword\">virtual<\/span> <span class=\"hljs-type\">void<\/span> <span class=\"hljs-title\">foo<\/span><span class=\"hljs-params\">()<\/span> <\/span>{}\r\n};\r\n\r\n<span class=\"hljs-keyword\">class<\/span> <span class=\"hljs-title class_\">Derived<\/span> : <span class=\"hljs-keyword\">public<\/span> Base {};\r\n\r\n<span class=\"hljs-function\"><span class=\"hljs-type\">int<\/span> <span class=\"hljs-title\">main<\/span><span class=\"hljs-params\">()<\/span> <\/span>{\r\n   Base* basePtr = <span class=\"hljs-keyword\">new<\/span> <span class=\"hljs-built_in\">Derived<\/span>();\r\n\r\n   <span class=\"hljs-comment\">\/\/ \u4f7f\u7528typeid\u83b7\u53d6basePtr\u6240\u6307\u5bf9\u8c61\u7684\u7c7b\u578b\u4fe1\u606f<\/span>\r\n   <span class=\"hljs-type\">const<\/span> std::type_info&amp; type = <span class=\"hljs-built_in\">typeid<\/span>(*basePtr);\r\n\r\n   <span class=\"hljs-comment\">\/\/ \u6253\u5370\u7c7b\u578b\u7684\u540d\u79f0<\/span>\r\n   std::cout &lt;&lt; <span class=\"hljs-string\">\"Object type: \"<\/span> &lt;&lt; type.<span class=\"hljs-built_in\">name<\/span>() &lt;&lt; std::endl;\r\n\r\n   <span class=\"hljs-comment\">\/\/ \u4f7f\u7528typeid\u8fdb\u884c\u7c7b\u578b\u5224\u65ad<\/span>\r\n   <span class=\"hljs-keyword\">if<\/span> (type == <span class=\"hljs-built_in\">typeid<\/span>(Base)) {\r\n      std::cout &lt;&lt; <span class=\"hljs-string\">\"Object is of type Base\"<\/span> &lt;&lt; std::endl;\r\n   }\r\n   <span class=\"hljs-keyword\">else<\/span> <span class=\"hljs-keyword\">if<\/span> (type == <span class=\"hljs-built_in\">typeid<\/span>(Derived)) {\r\n      std::cout &lt;&lt; <span class=\"hljs-string\">\"Object is of type Derived\"<\/span> &lt;&lt; std::endl;\r\n   }\r\n\r\n   <span class=\"hljs-keyword\">delete<\/span> basePtr;\r\n   <span class=\"hljs-keyword\">return<\/span> <span class=\"hljs-number\">0<\/span>;\r\n}\r\n<\/code><\/pre>\n<p>The output result:<\/p>\n<pre class=\"post-pre\"><code>Object type: class Derived\r\nObject is of type Derived\r\n<\/code><\/pre>\n<p>In the example above, typeid(*basePtr) returns a type_info object with the name &#8220;class Derived&#8221;, indicating that the actual type of the object pointed to by basePtr is Derived.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The typeid in C++ is an operator used to retrieve the type information of an expression. It returns a std::type_info object that contains the type information of the expression, including the name of the type. The typeid is commonly used with dynamic_cast and std::type_info to identify the actual type of an object at runtime, allowing [&hellip;]<\/p>\n","protected":false},"author":14,"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":[3395,18714,18716,18717,18715],"class_list":["post-13922","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-c-rtti","tag-c-typeid","tag-runtime-type-identification","tag-stdtype_info","tag-typeid-operator"],"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>C++ typeid Explained: Purpose and Usage - Blog - Silicon Cloud<\/title>\n<meta name=\"description\" content=\"Discover how C++ typeid enables runtime type identification with std::type_info. 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