{"id":110186,"date":"2024-03-22T16:44:07","date_gmt":"2024-03-22T07:44:07","guid":{"rendered":"https:\/\/www.silicloud.com\/ja\/blog\/c%e3%81%aedecltype%e3%81%ae%e7%94%a8%e9%80%94\/"},"modified":"2024-03-27T17:57:30","modified_gmt":"2024-03-27T08:57:30","slug":"c%e3%81%aedecltype%e3%81%ae%e7%94%a8%e9%80%94","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/ja\/blog\/c%e3%81%aedecltype%e3%81%ae%e7%94%a8%e9%80%94\/","title":{"rendered":"C++\u306edecltype\u306e\u7528\u9014"},"content":{"rendered":"<p>decltype\u306fC++\u3067\u5909\u6570\u3084\u95a2\u6570\u306e\u578b\u3092\u5f0f\u304b\u3089\u63a8\u8ad6\u3059\u308b\u305f\u3081\u306e\u578b\u63a8\u8ad6\u30e1\u30ab\u30cb\u30ba\u30e0\u3067\u3059\u3002decltype\u306f\u5909\u6570\u5ba3\u8a00\u3001\u95a2\u6570\u8fd4\u308a\u5024\u578b\u3001\u30c6\u30f3\u30d7\u30ec\u30fc\u30c8\u30d1\u30e9\u30e1\u30fc\u30bf\u306a\u3069\u3001\u3055\u307e\u3056\u307e\u306a\u5834\u6240\u3067\u4f7f\u7528\u3067\u304d\u307e\u3059\u3002<\/p>\n<p>decltype\u306e\u69cb\u6587\u306f\u6b21\u306e\u3068\u304a\u308a\u3067\u3059\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"hljs-keyword\">decltype<\/span>(expression)\r\n<\/code><\/pre>\n<p>expression \u306f\u3001\u5909\u6570\u3001\u95a2\u6570\u547c\u51fa\u3057\u3001\u7b97\u8853\u6f14\u7b97\u3001\u578b\u5909\u63db\u306a\u3069\u3001\u6709\u52b9\u306a C++ \u5f0f\u3092\u4f55\u3067\u3082\u6307\u5b9a\u3067\u304d\u307e\u3059\u3002<\/p>\n<p>decltype\u306f\u3001\u5f0f\u306e\u7d50\u679c\u3092\u89e3\u6790\u3057\u3066\u5f0f\u306e\u578b\u3092\u63a8\u8ad6\u3059\u308b\u3053\u3068\u3067\u52d5\u4f5c\u3057\u307e\u3059\u3002decltype\u306f\u3001\u5f0f\u81ea\u4f53\u3092\u5b9f\u884c\u3059\u308b\u3053\u3068\u306a\u304f\u3001\u5f0f\u306e\u578b\u306b\u57fa\u3065\u3044\u3066\u578b\u3092\u8fd4\u3057\u307e\u3059\u3002<\/p>\n<p>decltype \u3092\u7528\u3044\u308b\u4e00\u822c\u7684\u306a\u7528\u9014\u3092\u4ee5\u4e0b\u306b\u793a\u3057\u307e\u3059\u3002<\/p>\n<ol>\n<li>\u5909\u6570\u5ba3\u8a00\uff1a<\/li>\n<\/ol>\n<pre class=\"post-pre\"><code><span class=\"hljs-type\">int<\/span> x = <span class=\"hljs-number\">10<\/span>;\r\n<span class=\"hljs-keyword\">decltype<\/span>(x) y;  <span class=\"hljs-comment\">\/\/ \u63a8\u5bfc\u51fa\u53d8\u91cfy\u7684\u7c7b\u578b\u4e3aint<\/span>\r\n<\/code><\/pre>\n<ol>\n<li>\u8fd4\u308a\u5024\u306e\u578b:<\/li>\n<\/ol>\n<pre class=\"post-pre\"><code><span class=\"hljs-function\"><span class=\"hljs-type\">int<\/span> <span class=\"hljs-title\">add<\/span><span class=\"hljs-params\">(<span class=\"hljs-type\">int<\/span> a, <span class=\"hljs-type\">int<\/span> b)<\/span> <\/span>{\r\n    <span class=\"hljs-keyword\">return<\/span> a + b;\r\n}\r\n\r\n<span class=\"hljs-function\"><span class=\"hljs-type\">double<\/span> <span class=\"hljs-title\">sub<\/span><span class=\"hljs-params\">(<span class=\"hljs-type\">double<\/span> a, <span class=\"hljs-type\">double<\/span> b)<\/span> <\/span>{\r\n    <span class=\"hljs-keyword\">return<\/span> a - b;\r\n}\r\n\r\n<span class=\"hljs-keyword\">decltype<\/span>(add) sum;  <span class=\"hljs-comment\">\/\/ \u63a8\u5bfc\u51fasum\u7684\u7c7b\u578b\u4e3aint(*)(int, int)<\/span>\r\n<span class=\"hljs-keyword\">decltype<\/span>(sub) diff; <span class=\"hljs-comment\">\/\/ \u63a8\u5bfc\u51fadiff\u7684\u7c7b\u578b\u4e3adouble(*)(double, double)<\/span>\r\n<\/code><\/pre>\n<ol>\n<li>\u30cd\u30a4\u30c6\u30a3\u30d6\u306b\u65e5\u672c\u8a9e\u3067\u8a00\u3044\u63db\u3048\u308b\u3068\uff1a<\/li>\n<\/ol>\n<pre class=\"post-pre\"><code><span class=\"hljs-keyword\">template<\/span> &lt;<span class=\"hljs-keyword\">typename<\/span> T, <span class=\"hljs-keyword\">typename<\/span> U&gt;\r\n<span class=\"hljs-function\"><span class=\"hljs-type\">void<\/span> <span class=\"hljs-title\">multiply<\/span><span class=\"hljs-params\">(T a, U b)<\/span> <\/span>{\r\n    <span class=\"hljs-keyword\">decltype<\/span>(a * b) result;  <span class=\"hljs-comment\">\/\/ \u63a8\u5bfc\u51faresult\u7684\u7c7b\u578b\u4e3aT<\/span>\r\n    <span class=\"hljs-comment\">\/\/ ...<\/span>\r\n}\r\n\r\n<span class=\"hljs-type\">int<\/span> x = <span class=\"hljs-number\">10<\/span>;\r\n<span class=\"hljs-type\">double<\/span> y = <span class=\"hljs-number\">3.5<\/span>;\r\n<span class=\"hljs-built_in\">multiply<\/span>(x, y);  <span class=\"hljs-comment\">\/\/ result\u7684\u7c7b\u578b\u4e3aint<\/span>\r\n<\/code><\/pre>\n<ol>\n<li>\u95a2\u6570\u306e\u623b\u308a\u5024\u306e\u578b\u3092\u81ea\u52d5\u63a8\u5b9a<\/li>\n<\/ol>\n<pre class=\"post-pre\"><code><span class=\"hljs-function\"><span class=\"hljs-keyword\">auto<\/span> <span class=\"hljs-title\">add<\/span><span class=\"hljs-params\">(<span class=\"hljs-type\">int<\/span> a, <span class=\"hljs-type\">int<\/span> b)<\/span> -&gt; <span class=\"hljs-title\">decltype<\/span><span class=\"hljs-params\">(a + b)<\/span> <\/span>{\r\n    <span class=\"hljs-keyword\">return<\/span> a + b;\r\n}\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    <span class=\"hljs-type\">int<\/span> x = <span class=\"hljs-number\">10<\/span>;\r\n    <span class=\"hljs-type\">int<\/span> y = <span class=\"hljs-number\">20<\/span>;\r\n    <span class=\"hljs-keyword\">decltype<\/span>(<span class=\"hljs-built_in\">add<\/span>(x, y)) sum = <span class=\"hljs-built_in\">add<\/span>(x, y);  <span class=\"hljs-comment\">\/\/ \u63a8\u5bfc\u51fasum\u7684\u7c7b\u578b\u4e3aint<\/span>\r\n    <span class=\"hljs-keyword\">return<\/span> <span class=\"hljs-number\">0<\/span>;\r\n}\r\n<\/code><\/pre>\n<p>\u7dcf\u3058\u3066\u3001decltype\u306b\u3088\u308a\u5f0f\u306e\u578b\u306e\u5c0e\u51fa\u304c\u7c21\u5358\u306b\u306a\u308a\u3001\u30b3\u30fc\u30c9\u306e\u67d4\u8edf\u6027\u3068\u6c4e\u7528\u6027\u3092\u5411\u4e0a\u3067\u304d\u307e\u3059\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>decltype\u306fC++\u3067\u5909\u6570\u3084\u95a2\u6570\u306e\u578b\u3092\u5f0f\u304b\u3089\u63a8\u8ad6\u3059\u308b\u305f\u3081\u306e\u578b\u63a8\u8ad6\u30e1\u30ab\u30cb\u30ba\u30e0\u3067\u3059\u3002decltype\u306f\u5909\u6570\u5ba3\u8a00\u3001\u95a2\u6570\u8fd4\u308a\u5024\u578b\u3001\u30c6\u30f3\u30d7\u30ec\u30fc\u30c8\u30d1\u30e9\u30e1\u30fc\u30bf\u306a\u3069\u3001\u3055\u307e\u3056\u307e\u306a\u5834\u6240\u3067\u4f7f\u7528\u3067\u304d\u307e\u3059\u3002 decltype\u306e\u69cb\u6587\u306f\u6b21\u306e\u3068\u304a\u308a [&hellip;]<\/p>\n","protected":false},"author":8,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-110186","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) - 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