{"id":362,"date":"2015-04-07T10:47:53","date_gmt":"2015-04-07T02:47:53","guid":{"rendered":"http:\/\/www.cgdev.net\/blog\/?p=362"},"modified":"2023-05-01T12:19:53","modified_gmt":"2023-05-01T04:19:53","slug":"c11-smart-pointers","status":"publish","type":"post","link":"https:\/\/www.cgdev.net\/blog\/362.html","title":{"rendered":"C++11 Smart Pointers"},"content":{"rendered":"<h3>\u4e00.\u00a0 unique_ptr<\/h3>\n<p>\u8fd9\u79cd\u6307\u9488\u521a\u597d\u548c shared_ptr \u76f8\u53cd: unique_ptr \u7981\u6b62\u4e86\u62f7\u8d1d\u6784\u9020\u51fd\u6570, \u56e0\u6b64\u4efb\u4f55\u65f6\u523b\u4e0d\u53ef\u80fd\u6709\u4e24\u4e2a unique_ptr \u6307\u5411\u540c\u4e00\u4e2a\u5bf9\u8c61, \u4e5f\u5c31\u662f\u8bf4\u5b83\u6ca1\u6709\u590d\u5236\u64cd\u4f5c. \u90a3\u4e48\u8981\u5c06\u6307\u9488\u8d4b\u7ed9\u53e6\u4e00\u4e2a\u6307\u9488\u600e\u4e48\u529e\u5462? \u8fd9\u5c31\u8981\u7528 std::move \u51fd\u6570\u6765\u79fb\u4ea4\u6240\u6709\u6743, \u79f0\u4e3a\u79fb\u52a8\u64cd\u4f5c.\u00a0 \u521b\u5efa\u64cd\u4f5c\u6700\u597d\u7528 C++14 \u5f15\u5165\u7684 std::make_unique \u66ff\u4ee3new, \u56e0\u4e3a\u8fd9\u53ef\u4ee5\u8ba9\u7f16\u8bd1\u5668\u4ea7\u751f\u66f4\u5c0f\u66f4\u5feb\u7684\u4ee3\u7801. \u91ca\u653e\u64cd\u4f5c\u4e3b\u8981\u6709\u4e24\u4e2a\u51fd\u6570: release \u91ca\u653e\u6240\u6709\u6743\u5e76\u8fd4\u56de\u539f\u59cb\u6307\u9488, reset \u4e0d\u5e26\u53c2\u6570\u7684\u8bdd\u5373\u91ca\u653e\u6240\u6709\u6743, \u5e26\u53c2\u6570\u7684\u8bdd\u5219\u8fd8\u80fd\u7ed1\u5b9a\u5230\u65b0\u5bf9\u8c61.<\/p>\n<pre>pointer release();\r\nvoid reset( pointer _Ptr = pointer() );\r\n<\/pre>\n<p>unique_ptr \u867d\u7136\u4e0d\u80fd\u590d\u5236, \u4f46\u5728\u51fd\u6570\u4e2d\u4f5c\u4e3a\u8fd4\u56de\u503c\u5374\u53ef\u4ee5\u8fd9\u6837\u7528:<\/p>\n<pre>unique_ptr&lt;int&gt; GetId() \r\n{\r\n\u00a0\u00a0 unique_ptr&lt;int&gt; p(new int(1));\r\n\u00a0\u00a0 return p;\r\n}\r\nunique_ptr&lt;int&gt; pID = GetId();<\/pre>\n<p>unique_ptr\u6709\u4e2a\u91cd\u8981\u7528\u5904\u662f\u5b83\u53ef\u4ee5\u7528\u4f5cstl\u5bb9\u5668\u5143\u7d20, \u4f46\u4e0d\u80fd\u76f4\u63a5push_back, \u800c\u662f\u9700\u8981\u7528move\u79fb\u4ea4\u6240\u6709\u6743\u7684\u65b9\u5f0f, \u5982\u4e0b<\/p>\n<pre>\u00a0\u00a0 unique_ptr&lt;int&gt; p(new int(2));\r\n\u00a0\u00a0 vector&lt;unique_ptr&lt;int&gt;&gt; v;\r\n\u00a0\u00a0 v.push_back(std::move(p));<\/pre>\n<p>\u53e6\u4e00\u4e2a\u91cd\u8981\u7528\u5904\u662f\u7f16\u5199\u5f02\u5e38\u5b89\u5168\u7684\u4ee3\u7801<\/p>\n<pre>void fun()\r\n{\r\n\u00a0\u00a0 unique_ptr&lt;int&gt; p(new int(2));\u00a0 \/\/\u5373\u4f7f\u4e0b\u9762\u53d1\u751f\u5f02\u5e38\u7684\u8bdd,\u4e5f\u80fd\u786e\u4fdd\u5bf9\u8c61\u88ab\u9500\u6bc1\r\n\u00a0\u00a0 show(p);\r\n\u00a0\u00a0 \/\/...\r\n}\r\n   \r\n<\/pre>\n<h3>\u4e8c. shared_ptr<\/h3>\n<p>shared_ptr \u5141\u8bb8\u591a\u4e2a\u6307\u9488\u6307\u5411\u540c\u4e00\u4e2a\u5bf9\u8c61, \u8fd9\u5c31\u548c unique_ptr \u76f8\u53cd<br \/>\n\u7528vc2008\u7684\u8bdd, \u9700\u8981\u5b89\u88c5sp1\u540e\u8fd9\u6837\u4f7f\u7528\u5b83std::tr1::shared_ptr, \u82e5\u662f\u4f7f\u7528\u65b0\u7248\u672c\u6bd4\u5982vc2015\u5219\u4e0d\u7528.<br \/>\nshared_ptr\u521b\u5efa\u64cd\u4f5c\u6700\u597d\u7528C++11\u5f15\u5165\u7684 std::make_shared \u66ff\u4ee3new; \u82e5\u8981\u83b7\u5f97\u666e\u901a\u6307\u9488\u53ef\u7528<span class=\"me1\">get\u51fd\u6570<\/span>; \u91ca\u653e\u6240\u6709\u6743\u662f\u7528reset\u51fd\u6570\u800c\u65e0release\u51fd\u6570; \u4ea4\u6362\u4e24\u4e2a<tt><span style=\"font-family: NSimsun;\">shared_ptr<\/span><\/tt>\u7528<tt><span style=\"font-family: NSimsun;\">swap<\/span><\/tt>\u51fd\u6570<\/p>\n<pre>void reset() \r\n{\u00a0\u00a0 \u00a0\r\n\u00a0\u00a0 shared_ptr().swap(*this); \/\/ release resource and convert to empty shared_ptr object\r\n}<\/pre>\n<p>\u8981\u6ce8\u610f\u9632\u6b62\u4ece\u4e00\u4e2a\u666e\u901a\u6307\u9488\u6784\u9020\u51fa\u4e24\u4e2a\u4ee5\u4e0a\u7684\u667a\u80fd\u6307\u9488, \u6bd4\u5982\u8fd9\u6837\u5199\u662f\u9519\u8bef\u7684<\/p>\n<pre>\u00a0\u00a0 int *p = new int(2);\r\n\u00a0\u00a0 shared_ptr&lt;int&gt; p1(p);\r\n\u00a0\u00a0 shared_ptr&lt;int&gt; p2(p); \/\/\u56e0\u4e3a\u4f7f\u7528\u4e86\u65b0\u5f15\u7528\u8ba1\u6570\u5668, \u6545\u4f1a\u53d1\u751f\u7b2c\u4e8c\u6b21\u9500\u6bc1<\/pre>\n<p>\u82e5\u8981\u5bf9\u6307\u9488\u6267\u884c\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u6bd4\u5982static_cast, \u6211\u4eec\u53ef\u4ee5\u53d6\u51fa\u666e\u901a\u6307\u9488\u7136\u540e\u8fdb\u884c\u5f3a\u5236\u8f6c\u6362, \u4f46\u4e0d\u8981\u628a\u5b83\u5b58\u5230\u53e6\u4e00\u4e2ashared_ptr\u91cc, \u56e0\u4e3a\u65b0\u7684 shared_ptr\u4f1a\u6709\u72ec\u7acb\u7684\u5f15\u7528\u8ba1\u6570\u5668, \u4ece\u800c\u53d1\u751f\u4e0a\u9762\u90a3\u79cd\u9519\u8bef\u3002\u5bf9\u4e8e\u8fd9\u79cd\u9700\u8981\u5f3a\u5236\u8f6c\u6362\u7684\u60c5\u5f62, \u5c31\u8981\u7528\u5230 static_pointer_cast \u6216\u8005 dynamic_pointer_cast \u624d\u80fd\u7ef4\u62a4\u6b63\u786e\u7684\u5f15\u7528\u8ba1\u6570<\/p>\n<pre>\u00a0\u00a0 \/\/\u5047\u8bbeCBox\u7ee7\u627f\u81eaCObject\r\n\u00a0\u00a0 shared_ptr&lt;CBase&gt; p(new CBox);\r\n\u00a0\u00a0 shared_ptr&lt;CBox&gt; pb = static_pointer_cast&lt;CBox&gt;(p);<\/pre>\n<p>\u5728\u5b9a\u4e49\u7c7b\u65f6\u8981\u6ce8\u610f\u9632\u6b62\u7c7b\u5bf9\u8c61\u672c\u8eab\u5f53\u4e2d\u4e0d\u80fd\u5b58\u50a8\u7c7b\u5bf9\u8c61\u672c\u8eab\u7684 shared_ptr, \u5426\u5219\u8fd9\u4e9b\u5bf9\u8c61\u6c38\u8fdc\u90fd\u4e0d\u4f1a\u88ab\u9500\u6bc1, \u540c\u6837\u4e5f\u8981\u9632\u6b62\u4f7f\u7528shared_ptr\u9020\u6210\u5bf9\u8c61\u4e92\u76f8\u4f9d\u8d56\u7684\u60c5\u5f62, \u5373\u7c7bA\u4e2d\u5b9a\u4e49\u4e86\u6307\u5411\u7c7bB\u5bf9\u8c61\u7684shared_ptr, \u7c7bB\u4e2d\u4e5f\u5b9a\u4e49\u4e86\u6307\u5411\u7c7bA\u5bf9\u8c61\u7684shared_ptr, \u90a3\u4e48\u5f53\u6211\u4eec\u4e3a\u8fd9\u4e24\u4e2a\u7c7b\u521b\u5efa\u51fa\u5bf9\u8c61\u540e, \u5b83\u4eec\u90fd\u4e0d\u80fd\u88ab\u9500\u6bc1\u4e86, \u5176\u672c\u8d28\u539f\u56e0\u662f\u80fd\u6700\u7ec8\u89e6\u53d1\u5bf9\u8c61\u9500\u6bc1\u7684\u4e24\u4e2a\u667a\u80fd\u6307\u9488\u6070\u597d\u662f\u4e24\u4e2a\u5bf9\u8c61\u5185\u7684\u6210\u5458, \u4ece\u800c\u4f7f\u4e24\u5bf9\u8c61\u7684\u751f\u5b58\u671f\u6784\u6210\u73af\u5f62\u4f9d\u8d56\u5173\u7cfb.<\/p>\n<pre>class B;\r\nclass A\r\n{\r\npublic:\r\n\u00a0\u00a0 shared_ptr&lt;B&gt; pb;\r\n\r\n\u00a0\u00a0 ~A()\r\n\u00a0\u00a0 {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 cout &lt;&lt; \"A end\\n\";\r\n\u00a0\u00a0 }\r\n};\r\n\r\nclass B\r\n{\r\npublic:\r\n\u00a0\u00a0 shared_ptr&lt;A&gt; pa;\r\n\u00a0 \u00a0\r\n\u00a0\u00a0 ~B()\r\n\u00a0\u00a0 {\r\n\u00a0\u00a0\u00a0\u00a0\u00a0 cout &lt;&lt; \"B end\\n\";\r\n\u00a0\u00a0 }\r\n};<\/pre>\n<h3>\u00a0\u4e09. weak_ptr<\/h3>\n<p>\u4e0a\u9762\u8c08\u5230shared_ptr \u7684\u5faa\u73af\u5f15\u7528\u4f1a\u9020\u6210\u5bf9\u8c61\u65e0\u6cd5\u88ab\u91ca\u653e\u4ece\u800c\u5bfc\u81f4\u5185\u5b58\u6cc4\u6f0f, \u800c\u8981\u76f8\u4e92\u4fdd\u5b58\u5bf9\u65b9\u7684\u667a\u80fd\u6307\u9488\u600e\u4e48\u529e\u5462, \u8fd9\u5c31\u8981\u7528weak_ptr, \u5b83\u76f8\u5f53\u4e8e shared_ptr \u7684\u89c2\u5bdf\u8005, \u4e0d\u4f1a\u589e\u52a0\u6307\u9488\u7684\u5f15\u7528\u8ba1\u6570, \u4e0d\u4f1a\u53bb\u7ba1\u7406\u5bf9\u8c61\u7684\u751f\u5b58\u671f, \u4ece\u800c\u4e0d\u4f1a\u5bfc\u81f4\u5faa\u73af\u7684\u4f9d\u8d56\u94fe.<\/p>\n<p>\u5728\u9700\u8981shared_ptr\u7684\u65f6\u5019\u7528lock()\u51fd\u6570; \u7528\u51fd\u6570use_count()\u53ef\u4ee5\u89c2\u6d4b\u5f15\u7528\u8ba1\u6570, \u51fd\u6570expired()\u7b49\u4ef7\u4e8e use_count()==0 \u7528\u4e8e\u5224\u65ad\u5bf9\u8c61\u662f\u5426\u5df2\u91ca\u653e<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e00.\u00a0 unique_ptr \u8fd9\u79cd\u6307\u9488\u521a\u597d\u548c shared_ptr \u76f8\u53cd: unique_ptr \u7981\u6b62\u4e86\u62f7\u8d1d\u6784\u9020\u51fd\u6570, \u56e0\u6b64\u4efb\u4f55\u65f6\u523b\u4e0d\u53ef\u80fd\u6709\u4e24\u4e2a unique_ptr \u6307\u5411\u540c\u4e00\u4e2a\u5bf9\u8c61, \u4e5f\u5c31\u662f\u8bf4\u5b83\u6ca1\u6709\u590d\u5236\u64cd\u4f5c. \u90a3\u4e48\u8981\u5c06\u6307\u9488\u8d4b\u7ed9\u53e6\u4e00\u4e2a\u6307\u9488\u600e\u4e48\u529e\u5462? \u8fd9\u5c31\u8981\u7528 std::move \u51fd\u6570\u6765\u79fb\u4ea4\u6240\u6709\u6743, \u79f0\u4e3a\u79fb\u52a8\u64cd\u4f5c.\u00a0 \u521b\u5efa\u64cd\u4f5c\u6700\u597d\u7528 C++14 \u5f15\u5165\u7684 std::make_unique \u66ff\u4ee3new, \u56e0\u4e3a\u8fd9\u53ef\u4ee5\u8ba9\u7f16\u8bd1\u5668\u4ea7\u751f\u66f4\u5c0f\u66f4\u5feb\u7684\u4ee3\u7801. \u91ca\u653e\u64cd\u4f5c\u4e3b\u8981\u6709\u4e24\u4e2a\u51fd\u6570: release \u91ca\u653e\u6240\u6709\u6743\u5e76\u8fd4\u56de\u539f\u59cb\u6307\u9488, reset \u4e0d\u5e26\u53c2\u6570\u7684\u8bdd\u5373\u91ca\u653e\u6240\u6709\u6743, \u5e26\u53c2\u6570\u7684\u8bdd\u5219\u8fd8\u80fd\u7ed1\u5b9a\u5230\u65b0\u5bf9\u8c61. pointer release(); void reset( pointer _Ptr = pointer() ); unique_ptr \u867d\u7136\u4e0d\u80fd\u590d\u5236, \u4f46\u5728\u51fd\u6570\u4e2d\u4f5c\u4e3a\u8fd4\u56de\u503c\u5374\u53ef\u4ee5\u8fd9\u6837\u7528: unique_ptr&lt;int&gt; GetId() { \u00a0\u00a0 unique_ptr&lt;int&gt; p(new int(1)); \u00a0\u00a0 return p; } unique_ptr&lt;int&gt; pID = GetId(); [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"class_list":["post-362","post","type-post","status-publish","format-standard","hentry","category-cpp"],"_links":{"self":[{"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/posts\/362","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/comments?post=362"}],"version-history":[{"count":0,"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/posts\/362\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/media?parent=362"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/categories?post=362"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cgdev.net\/blog\/wp-json\/wp\/v2\/tags?post=362"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}