{"id":10001,"date":"2024-03-14T10:26:11","date_gmt":"2024-03-14T10:26:11","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/how-to-sort-a-c-hash-table\/"},"modified":"2025-08-03T17:59:32","modified_gmt":"2025-08-03T17:59:32","slug":"how-to-sort-a-c-hash-table","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/how-to-sort-a-c-hash-table\/","title":{"rendered":"Sorting C++ unordered_map: Simple Guide"},"content":{"rendered":"<p>In C++, hash tables are unordered data structures, so they cannot be sorted directly. If sorting elements within a hash table is necessary, you can copy the elements to a new container (such as a vector) and then sort that container.<\/p>\n<p>Here is a sample code demonstrating how to copy elements from a hash map to a vector and sort them.<\/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;unordered_map&gt;<\/span><\/span>\r\n<span class=\"hljs-meta\">#<span class=\"hljs-keyword\">include<\/span> <span class=\"hljs-string\">&lt;vector&gt;<\/span><\/span>\r\n<span class=\"hljs-meta\">#<span class=\"hljs-keyword\">include<\/span> <span class=\"hljs-string\">&lt;algorithm&gt;<\/span><\/span>\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    std::unordered_map&lt;<span class=\"hljs-type\">int<\/span>, std::string&gt; hashTable = {\r\n        {<span class=\"hljs-number\">1<\/span>, <span class=\"hljs-string\">\"apple\"<\/span>},\r\n        {<span class=\"hljs-number\">3<\/span>, <span class=\"hljs-string\">\"banana\"<\/span>},\r\n        {<span class=\"hljs-number\">2<\/span>, <span class=\"hljs-string\">\"orange\"<\/span>}\r\n    };\r\n\r\n    std::vector&lt;std::pair&lt;<span class=\"hljs-type\">int<\/span>, std::string&gt;&gt; <span class=\"hljs-built_in\">vec<\/span>(hashTable.<span class=\"hljs-built_in\">begin<\/span>(), hashTable.<span class=\"hljs-built_in\">end<\/span>());\r\n\r\n    <span class=\"hljs-comment\">\/\/ \u5bf9vector\u4e2d\u7684\u5143\u7d20\u8fdb\u884c\u6392\u5e8f<\/span>\r\n    std::<span class=\"hljs-built_in\">sort<\/span>(vec.<span class=\"hljs-built_in\">begin<\/span>(), vec.<span class=\"hljs-built_in\">end<\/span>(), [](<span class=\"hljs-type\">const<\/span> std::pair&lt;<span class=\"hljs-type\">int<\/span>, std::string&gt;&amp; a, <span class=\"hljs-type\">const<\/span> std::pair&lt;<span class=\"hljs-type\">int<\/span>, std::string&gt;&amp; b) {\r\n        <span class=\"hljs-keyword\">return<\/span> a.first &lt; b.first;\r\n    });\r\n\r\n    <span class=\"hljs-comment\">\/\/ \u6253\u5370\u6392\u5e8f\u540e\u7684\u7ed3\u679c<\/span>\r\n    <span class=\"hljs-keyword\">for<\/span> (<span class=\"hljs-type\">const<\/span> <span class=\"hljs-keyword\">auto<\/span>&amp; pair : vec) {\r\n        std::cout &lt;&lt; pair.first &lt;&lt; <span class=\"hljs-string\">\": \"<\/span> &lt;&lt; pair.second &lt;&lt; std::endl;\r\n    }\r\n\r\n    <span class=\"hljs-keyword\">return<\/span> <span class=\"hljs-number\">0<\/span>;\r\n}\r\n<\/code><\/pre>\n<p>In the example above, the elements in the hash table are first copied to a vector, then the elements in the vector are sorted using the std::sort function, and finally the sorted results are printed.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>In C++, hash tables are unordered data structures, so they cannot be sorted directly. If sorting elements within a hash table is necessary, you can copy the elements to a new container (such as a vector) and then sort that container. Here is a sample code demonstrating how to copy elements from a hash map [&hellip;]<\/p>\n","protected":false},"author":5,"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":[5425,5148,12195,12196,12197],"class_list":["post-10001","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-c-code-example","tag-c-containers","tag-c-unordered_map","tag-sort-hash-table","tag-stdvector-sort"],"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>Sorting C++ unordered_map: Simple Guide - Blog - Silicon Cloud<\/title>\n<meta name=\"description\" content=\"Learn how to sort C++ unordered_map elements by copying to vectors. 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