{"id":645,"date":"2015-12-27T19:08:05","date_gmt":"2015-12-27T11:08:05","guid":{"rendered":"http:\/\/yangwang.hk\/?p=645"},"modified":"2015-12-27T19:08:05","modified_gmt":"2015-12-27T11:08:05","slug":"%e5%b2%94%e8%b7%af%e5%8f%a3%e3%80%81%e6%9c%aa%e5%ae%9a%e4%b9%89%e8%a1%8c%e4%b8%baundefined-behavior%ef%bc%8cub%e8%a1%8c%e4%b8%ba","status":"publish","type":"post","link":"https:\/\/yangwang.hk\/?p=645","title":{"rendered":"\u5c94\u8def\u53e3\u3001\u672a\u5b9a\u4e49\u884c\u4e3a(undefined behavior\uff0cub\u884c\u4e3a)"},"content":{"rendered":"

\u5728\u4e0a\u4e00\u7bc7\u6587\u7ae0\u4e2d\u6211\u4eec\u8bf4\u5230\uff0c\u4e0d\u5e94\u8be5\u5728\u4e00\u4e2a\u8868\u8fbe\u5f0f\u5185\u8fdb\u884c\u591a\u4e2a\u201c\u81ea\u589e\u201d\uff0c\u201c\u81ea\u51cf\u201d\u64cd\u4f5c<\/p>\n

\u539f\u56e0\u662f\u8fd9\u662f\u4e00\u4e2a\u672a\u5b9a\u4e49\u884c\u4e3a\uff0c\u90a3\u4e48\u4ec0\u4e48\u662f\u672a\u5b9a\u4e49\u884c\u4e3a\u5462\uff1f<\/p>\n

\u5728C\u8bed\u8a00\u6807\u51c6\u4e2d\uff0c\u6709\u4e00\u7c7b\u884c\u4e3a\u6ca1\u6709\u88ab\u89c4\u5b9a\uff0c\u8fd9\u6837\u4e00\u4e9b\u884c\u4e3a\u4fbf\u662f\u672a\u5b9a\u4e49\u884c\u4e3a\uff08Undefined Behavior\uff0c\u6709\u65f6\u79f0\u4e3aUB\u6216UB\u884c\u4e3a\uff09<\/p>\n

\u5982\u679c\u4f60\u7684\u7a0b\u5e8f\u4e2d\u6709\u672a\u5b9a\u4e49\u884c\u4e3a\uff0c\u90a3\u4e48\u8fd9\u4e2a\u7a0b\u5e8f\u7684\u7ed3\u679c\u4e0d\u662f\u786e\u5b9a\u7684\u3002\u6362\u53e5\u8bdd\u8bf4\uff0c\u5c31\u662f\u4f60\u7684\u7a0b\u5e8f\u5728\u4e0d\u540c\u7684\u7f16\u8bd1\u5668\u4e0a\u53ef\u80fd\u4f1a\u5f97\u5230\u5b8c\u5168\u4e0d\u540c\u7684\u7ed3\u679c\uff08\u4f8b\u5982\u4e0a\u4e00\u7bc7\u6587\u7ae0\u4e2d\u7684\u4f8b\u5b50\uff09\u3002<\/p>\n

\u90a3\u4e48\u4f60\u53ef\u80fd\u4f1a\u4e3a\uff0c\u90a3\u4e48\u4e3a\u4ec0\u4e48c\u6807\u51c6\u4e0d\u5bf9\u8fd9\u4e9b\u884c\u4e3a\u505a\u51fa\u89c4\u5b9a\u5462\uff1f\u96be\u9053\u662f\u758f\u6f0f\u4e48\uff1f<\/p>\n

\u7b54\u6848\u662f\u5426\u5b9a\u7684\uff0c\u89c4\u5b9a\u7684\u5236\u5b9a\u8005\u4eec\u65e9\u5c31\u8003\u8651\u5230\u4e86\u8fd9\u4e9b\u95ee\u9898\u3002\u7136\u800c\u76f8\u5bf9\u4e8e\u5c06\u8fd9\u4e9b\u884c\u4e3a\u786e\u5b9a\u4e0b\u6765\uff0c\u5bf9\u8fd9\u4e9b\u884c\u4e3a\u4e0d\u505a\u89c4\u5b9a\u4f3c\u4e4e\u662f\u4e00\u4e2a\u66f4\u597d\u7684\u9009\u62e9\uff0c\u56e0\u4e3a\u5b83\u7ed9\u7f16\u8bd1\u5668\u5bf9\u7a0b\u5e8f\u8fdb\u884c\u4f18\u5316\u63d0\u4f9b\u4e86\u7a7a\u95f4<\/p>\n

\u6bd5\u7adf\uff0cc\u8bed\u8a00\u76f8\u6bd4\u5176\u5b83\u8bed\u8a00\u7684\u4e00\u5927\u7279\u70b9\u4fbf\u662f\u66f4\u9ad8\u7684\u6267\u884c\u6548\u7387\uff0c\u7528\u51e0\u4e2aUB\u884c\u4e3a\u6765\u6362\u53d6\u66f4\u9ad8\u7684\u6548\u7387\uff0c\u5728\u4e00\u5b9a\u7a0b\u5ea6\u4e0a\u6216\u8bb8\u662f\u53ef\u4ee5\u63a5\u53d7\u7684\u3002<\/p>\n

\u6216\u8bb8\uff0c\u201c\u672a\u5b9a\u4e49\u884c\u4e3a\u201d\u662f\u4e00\u4e2a\u5931\u8d25\u7684\u7ffb\u8bd1\uff0c\u5018\u82e5\u5c06\u5176\u7ffb\u8bd1\u4e3a\u201c\u4e0d\u5b9a\u4e49\u884c\u4e3a\u201d\uff0c\u624d\u662f\u5176\u771f\u5b9e\u7684\u610f\u4e49 \":mrgreen:\"<\/p>\n

\u90a3\u4e48\u6709\u54ea\u4e9b\u672a\u5b9a\u4e49\u884c\u4e3a\u5462\uff1f<\/p>\n

\u4e00\u4e2a\u5f88\u5e38\u89c1\u7684\u672a\u5b9a\u4e49\u884c\u4e3a\u4fbf\u662f\u5728\u4e00\u4e2a\u8868\u8fbe\u5f0f\u4e2d\u4fee\u6539\u4e86\u67d0\u4e00\u4e2a\u503c\uff0c\u800c\u8fd9\u4e2a\u503c\u53c8\u5728\u8be5\u8868\u8fbe\u5f0f\u4e2d\u88ab\u4f7f\u7528<\/p>\n

\u4f8b\u5982\uff1a<\/p>\n

\r\nint foo = 0;\r\nfoo += foo++;\r\n<\/pre>\n
\u5c06\u8fd9\u4e2a\u8868\u8fbe\u5f0f\u5c55\u5f00\u540e\uff0c\u4f60\u5c06\u5f97\u5230foo = foo + foo++;<\/p>\n
\u8fd9\u6837\u95ee\u9898\u4fbf\u6765\u4e86\uff0c\u5982\u679c\u7f16\u8bd1\u5668\u5148\u8ba1\u7b97+=\u5de6\u8fb9\u7684\u503c\uff0c\u53730\uff0c\u63a5\u7740\u518d\u8ba1\u7b97foo++\uff0c\u5b83\u7684\u503c\u4e5f\u662f0\uff0c\u800cfoo\u5219\u662f1\u30020+0\uff0c\u4f60\u6700\u540e\u5c06\u5f97\u52300<\/p>\n
\u5982\u679c\u5148\u8ba1\u7b97foo++\uff0c\u5b83\u7684\u503c\u662f0\uff0c\u800cfoo\u5219\u6210\u4e861\uff0c\u8fd9\u65f6\u82e5\u518d\u5c06\u4e24\u8005\u76f8\u52a0\uff0c\u4f60\u5c06\u5f97\u52301+0\u4e5f\u5c31\u662f1\u8fd9\u4e2a\u7ed3\u679c<\/p>\n
\u4e0d\u540c\u7684\u8ba1\u7b97\u987a\u5e8f\u5c06\u5f97\u5230\u4e0d\u540c\u7684\u7ed3\u679c\uff0c\u800cC\u6807\u51c6\u4e2d\u6b63\u597d\u6ca1\u6709\u5bf9\u6b64\u8fdb\u884c\u89c4\u5b9a<\/p>\n
\u53e6\u4e00\u4e2a\u4f8b\u5b50\u662f<\/p>\n
\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\nint main(void)\r\n{\r\n    int foo = 0;\r\n\tprintf("%d %d %d", foo, foo++, foo);\r\n\treturn 0;\r\n}\r\n<\/pre>\n
\u4f60\u8ba4\u4e3a\u8f93\u51fa\u7ed3\u679c\u4f1a\u662f\u4ec0\u4e48\u5462\uff1f<\/p>\n
0 0 0\u4e48\uff1f1 0 0\u6216\u80050 0 1\uff1f<\/p>\n
\u7136\u800c\u7b54\u6848\u662f\u90fd\u4e0d\u662f\uff01<\/p>\n
\u5982\u679c\u4f60\u4f7f\u7528gcc\u7f16\u8bd1\u5668\uff0c\u4f60\u5c06\u5f97\u52301 0 1\uff0c\u5982\u4e0b\u56fe<\/p>\n
\"ub\"<\/a><\/p>\n
\u6ca1\u9519\uff0c\u8fd9\u4e5f\u662f\u4e00\u4e2a\u672a\u5b9a\u4e49\u884c\u4e3a\uff01<\/p>\n
\u663e\u7136\uff0c\u4f60\u7684\u7a0b\u5e8f\u4e2d\u5982\u679c\u6709\u672a\u5b9a\u4e49\u884c\u4e3a\uff0c\u6216\u8bb8\u6b63\u5982\u8bed\u8a00\u6807\u51c6\u6240\u8bf4\uff0c\u201c\u4ec0\u4e48\u4e8b\u60c5\u90fd\u53ef\u80fd\u53d1\u751f\u201d\u3002\u5f53\u7136\u4e5f\u8bb8\u4ec0\u4e48\u90fd\u6ca1\u6709\u53d1\u751f\u3002<\/p>\n
\u672a\u5b9a\u4e49\u884c\u4e3a\u5e76\u4e0d\u662f\u4e25\u683c\u610f\u4e49\u4e0a\u7684\u9519\u8bef\uff0c\u56e0\u4e3a\u4eba\u5bb6\u662f\u7b26\u5408\u8bed\u6cd5\u7684\u3002\u800c\u4e14c\u8bed\u8a00\u6807\u51c6\u4e5f\u5e76\u6ca1\u6709\u8981\u6c42\u7f16\u8bd1\u5668\u53bb\u68c0\u67e5\u8fd9\u4e9b\u672a\u5b9a\u4e49\u884c\u4e3a<\/p>\n
\u56e0\u6b64\uff0c\u4f60\u5e94\u8be5\u5c06\u8fd9\u4e9b\u884c\u4e3a\u719f\u8bb0\u4e8e\u5fc3\uff0c\u5e76\u8fdc\u79bb\u5b83\u4eec<\/p>\n
\u672a\u5b9a\u4e49\u884c\u4e3a\u8fd8\u6709\u597d\u591a\uff0c\u6211\u4eec\u5c06\u5728\u540e\u9762\u5b66\u4e60\u65b0\u77e5\u8bc6\u7684\u65f6\u5019\u6307\u51fa\uff0c\u8bf7\u7559\u5fc3\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"
\u5728\u4e0a\u4e00\u7bc7\u6587\u7ae0\u4e2d\u6211\u4eec\u8bf4\u5230\uff0c\u4e0d\u5e94\u8be5\u5728\u4e00\u4e2a\u8868\u8fbe\u5f0f\u5185\u8fdb\u884c\u591a\u4e2a\u201c\u81ea\u589e\u201d\uff0c\u201c\u81ea\u51cf\u201d\u64cd\u4f5c \u539f\u56e0\u662f\u8fd9\u662f\u4e00\u4e2a\u672a\u5b9a\u4e49\u884c\u4e3a\uff0c\u90a3\u4e48\u4ec0\u4e48\u2026 Read More: \u5c94\u8def\u53e3\u3001\u672a\u5b9a\u4e49\u884c\u4e3a(\u2026 »<\/a><\/span><\/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-645","post","type-post","status-publish","format-standard","hentry","category-c"],"views":2873,"_links":{"self":[{"href":"https:\/\/yangwang.hk\/index.php?rest_route=\/wp\/v2\/posts\/645","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/yangwang.hk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/yangwang.hk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/yangwang.hk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/yangwang.hk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=645"}],"version-history":[{"count":1,"href":"https:\/\/yangwang.hk\/index.php?rest_route=\/wp\/v2\/posts\/645\/revisions"}],"predecessor-version":[{"id":647,"href":"https:\/\/yangwang.hk\/index.php?rest_route=\/wp\/v2\/posts\/645\/revisions\/647"}],"wp:attachment":[{"href":"https:\/\/yangwang.hk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=645"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/yangwang.hk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=645"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/yangwang.hk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=645"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}