{"id":261293,"date":"2024-05-15T13:59:08","date_gmt":"2024-05-15T05:59:08","guid":{"rendered":"https:\/\/docs.pingcode.com\/ask\/ask-ask\/261293.html"},"modified":"2024-05-15T13:59:15","modified_gmt":"2024-05-15T05:59:15","slug":"%e5%a6%82%e4%bd%95%e5%9c%a8-c-%e4%bb%a3%e7%a0%81%e4%b8%ad%e6%8f%90%e7%a4%ba%e7%bc%96%e8%af%91%e5%99%a8%e6%9f%90%e4%b8%aa%e5%88%86%e6%94%af%e7%9a%84%e6%89%a7%e8%a1%8c%e6%a6%82%e7%8e%87%e9%ab%98","status":"publish","type":"post","link":"https:\/\/docs.pingcode.com\/ask\/261293.html","title":{"rendered":"\u5982\u4f55\u5728 C \u4ee3\u7801\u4e2d\u63d0\u793a\u7f16\u8bd1\u5668\u67d0\u4e2a\u5206\u652f\u7684\u6267\u884c\u6982\u7387\u9ad8"},"content":{"rendered":"

\"\u5982\u4f55\u5728<\/p>\n

\u51fd\u6570\u5206\u652f\u9884\u6d4b\u662f\u4e00\u79cd\u8ba9\u7f16\u8bd1\u5668\u63d0\u524d\u77e5\u6653\u4ee3\u7801\u4e2d\u7279\u5b9a\u6761\u4ef6\u5206\u652f\u6267\u884c\u9891\u7387\u7684\u6280\u672f\u3001\u53ef\u901a\u8fc7\u624b\u52a8\u63d0\u793a\u6216\u4f7f\u7528\u5185\u5efa\u9884\u6d4b\u51fd\u6570\u6765\u5b9e\u73b0\u3002\u5728C\u7a0b\u5e8f\u4e2d\uff0c\u60a8\u53ef\u4ee5\u4f7f\u7528\u5185\u8054\u6c47\u7f16\u3001GCC\u7684__builtin_expect<\/code>\u51fd\u6570\u4ee5\u53caC++20\u7684[[likely]]<\/code>\u548c[[unlikely]]<\/code>\u5c5e\u6027\u6765\u63d0\u793a\u7f16\u8bd1\u5668\u54ea\u4e2a\u5206\u652f\u7684\u6267\u884c\u6982\u7387\u66f4\u9ad8\u3002\u4f7f\u7528\u8fd9\u4e9b\u65b9\u6cd5\u53ef\u5e2e\u52a9\u7f16\u8bd1\u5668\u4f18\u5316\u4ee3\u7801\uff0c\u63d0\u9ad8\u7a0b\u5e8f\u8fd0\u884c\u6548\u7387\uff0c\u5c24\u5176\u662f\u5728\u70ed\u8def\u5f84\u4e0a\u66f4\u4e3a\u663e\u8457\u3002<\/strong><\/p>\n<\/p>\n

\u63a5\u4e0b\u6765\uff0c\u6211\u4f1a\u8be6\u7ec6\u4ecb\u7ecd\u5982\u4f55\u4f7f\u7528GCC\u7684__builtin_expect<\/code>\u51fd\u6570\u3001\u5229\u7528[[likely]]<\/code>\u548c[[unlikely]]<\/code>\u5c5e\u6027\uff0c\u4ee5\u53ca\u5982\u4f55\u5411\u7f16\u8bd1\u5668\u624b\u52a8\u63d0\u4f9b\u8fd9\u79cd\u5206\u652f\u9884\u6d4b\u4fe1\u606f\u3002<\/p>\n<\/p>\n

\u4e00\u3001GCC __BUILTIN_EXPECT<\/code><\/h3>\n<\/p>\n

GCC\u63d0\u4f9b\u4e86\u4e00\u4e2a\u5185\u7f6e\u51fd\u6570__builtin_expect<\/code>\uff0c\u8be5\u51fd\u6570\u53ef\u4ee5\u8ba9\u7a0b\u5e8f\u5458\u63d0\u4f9b\u5173\u4e8e\u5206\u652f\u9884\u6d4b\u7684\u663e\u5f0f\u4fe1\u606f\u3002\u683c\u5f0f\u5982\u4e0b\uff1a<\/p>\n<\/p>\n

long __builtin_expect(long exp, long c);<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u5b83\u544a\u8bc9\u7f16\u8bd1\u5668\uff0c\u8868\u8fbe\u5f0fexp<\/code>\u7684\u503c\u4e0ec<\/code>\u76f8\u7b49\u7684\u6982\u7387\u5f88\u9ad8\u3002\u5e38\u7528\u4e8eif<\/code>\u8bed\u53e5\u4e2d\uff0c\u5e2e\u52a9\u7f16\u8bd1\u5668\u8fdb\u884c\u5206\u652f\u9884\u6d4b\u3002<\/p>\n<\/p>\n
\u4f8b\u5982<\/strong>\uff0c\u4ee5\u4e0b\u662f\u6b64\u51fd\u6570\u5728\u5b9e\u9645if\u8bed\u53e5\u4e2d\u7684\u7528\u6cd5\uff1a<\/p>\n<\/p>\n
if (__builtin_expect(x > 0, 1)) {<\/p>\n
    \/\/ \u9ad8\u6982\u7387\u6267\u884c\u7684\u4ee3\u7801<\/p>\n
} else {<\/p>\n
    \/\/ \u4f4e\u6982\u7387\u6267\u884c\u7684\u4ee3\u7801<\/p>\n
}<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u8fd9\u91cc\uff0c__builtin_expect<\/code>\u544a\u8bc9\u7f16\u8bd1\u5668\uff0c\u6761\u4ef6x > 0<\/code>\u4e3a\u771f\u7684\u60c5\u51b5\u6982\u7387\u8f83\u9ad8\uff0c\u56e0\u6b64\u53ef\u80fd\u4f1a\u5bf9\u8fd9\u4e00\u5206\u652f\u7684\u4ee3\u7801\u8fdb\u884c\u4f18\u5316\u3002<\/p>\n<\/p>\n
\u4f7f\u7528\u573a\u666f\u5206\u6790<\/h4>\n<\/p>\n
\u5f53\u4f60\u80fd\u591f\u9884\u6d4b\u67d0\u4e2a\u6761\u4ef6\u7684\u7ed3\u679c\u65f6\uff0c\u5c31\u53ef\u4ee5\u4f7f\u7528__builtin_expect<\/code>\u6765\u544a\u77e5\u7f16\u8bd1\u5668\u3002\u5e38\u89c1\u7684\u4f7f\u7528\u573a\u666f\u5305\u62ec\u9519\u8bef\u5904\u7406\u4ee3\u7801\u3001\u5faa\u73af\u9000\u51fa\u6761\u4ef6\u7b49\u3002<\/p>\n<\/p>\n
\u4e8c\u3001C++20 [[LIKELY]]<\/code> \u548c [[UNLIKELY]]<\/code> \u5c5e\u6027<\/h3>\n<\/p>\n
\u5c3d\u7ba1__builtin_expect<\/code>\u5728C\u7a0b\u5e8f\u4e2d\u975e\u5e38\u6709\u7528\uff0cC++20\u66f4\u8fdb\u4e00\u6b65\u63d0\u4f9b\u4e86\u6807\u51c6\u7684\u65b9\u5f0f\u6765\u6307\u793a\u7f16\u8bd1\u5668\u4f18\u5316\u6700\u53ef\u80fd\uff08\u6216\u4e0d\u592a\u53ef\u80fd\uff09\u7684\u4ee3\u7801\u8def\u5f84\uff0c\u5f15\u5165\u4e86[[likely]]<\/code>\u548c[[unlikely]]<\/code>\u5c5e\u6027\u3002<\/p>\n<\/p>\n
[[LIKELY]]<\/code><\/h4>\n<\/p>\n
\u5728C++20\u4e2d\uff0c\u53ef\u4ee5\u901a\u8fc7\u5982\u4e0b\u65b9\u5f0f\u4f7f\u7528[[likely]]<\/code>\u5c5e\u6027\uff1a<\/p>\n<\/p>\n
if (x > 0) [[likely]] {<\/p>\n
    \/\/ \u9ad8\u6982\u7387\u6267\u884c\u7684\u4ee3\u7801<\/p>\n
} else {<\/p>\n
    \/\/ \u4f4e\u6982\u7387\u6267\u884c\u7684\u4ee3\u7801<\/p>\n
}<\/p>\n
<\/code><\/pre>\n<\/p>\n
[[UNLIKELY]]<\/code><\/h4>\n<\/p>\n
\u7c7b\u4f3c\u5730\uff0c[[unlikely]]<\/code>\u544a\u77e5\u7f16\u8bd1\u5668\u67d0\u5206\u652f\u7684\u6267\u884c\u6982\u7387\u4f4e\uff1a<\/p>\n<\/p>\n
if (x < 0) [[unlikely]] {<\/p>\n
    \/\/ \u4f4e\u6982\u7387\u6267\u884c\u7684\u4ee3\u7801<\/p>\n
} else {<\/p>\n
    \/\/ \u9ad8\u6982\u7387\u6267\u884c\u7684\u4ee3\u7801<\/p>\n
}<\/p>\n
<\/code><\/pre>\n<\/p>\n
\u4f7f\u7528\u8fd9\u4e24\u4e2a\u5c5e\u6027\u53ef\u4ee5\u66f4\u6e05\u6670\u5730\u8868\u8fbe\u7a0b\u5e8f\u5458\u7684\u610f\u56fe\uff0c\u5e76\u5e2e\u52a9\u7f16\u8bd1\u5668\u505a\u51fa\u66f4\u5408\u7406\u7684\u4f18\u5316\u51b3\u7b56\u3002<\/strong><\/p>\n<\/p>\n
\u4e09\u3001\u6027\u80fd\u4f18\u5316\u4e0e\u4ee3\u7801\u7ef4\u62a4<\/h3>\n<\/p>\n
\u867d\u7136\u5206\u652f\u9884\u6d4b\u4f18\u5316\u53ef\u4ee5\u63d0\u5347\u6027\u80fd\uff0c\u4f46\u5b83\u4e5f\u6709\u53ef\u80fd\u4f7f\u4ee3\u7801\u66f4\u96be\u7ef4\u62a4\u3002\u56e0\u6b64\uff0c\u53ea\u6709\u5f53\u6027\u80fd\u74f6\u9888\u5df2\u660e\u786e\uff0c\u4e14\u901a\u8fc7\u6027\u80fd\u5206\u6790\u786e\u8ba4\u5206\u652f\u9884\u6d4b\u786e\u5b9e\u53ef\u4ee5\u5e26\u6765\u663e\u8457\u6539\u8fdb\u65f6\uff0c\u624d\u5e94\u4f7f\u7528\u8fd9\u4e9b\u6280\u80fd\u3002<\/p>\n<\/p>\n
\u4ee3\u7801\u7684\u53ef\u8bfb\u6027\u5bf9\u4e8e\u7ef4\u62a4\u975e\u5e38\u5173\u952e<\/strong>\uff0c\u8fc7\u5ea6\u6216\u4e0d\u5f53\u4f7f\u7528\u5206\u652f\u9884\u6d4b\u4f18\u5316\u53ef\u80fd\u4f1a\u4f7f\u5f97\u4ee3\u7801\u96be\u4ee5\u7406\u89e3\u3002\u4e14\u968f\u7740\u7f16\u8bd1\u5668\u7684\u8fdb\u6b65\uff0c\u81ea\u52a8\u5206\u652f\u9884\u6d4b\u7684\u51c6\u786e\u6027\u4e5f\u5728\u4e0d\u65ad\u63d0\u9ad8\uff0c\u964d\u4f4e\u4e86\u624b\u52a8\u4f18\u5316\u7684\u5fc5\u8981\u6027\u3002<\/p>\n<\/p>\n
\u56db\u3001\u5b9e\u8df5\u4e2d\u7684\u6ce8\u610f\u4e8b\u9879<\/h3>\n<\/p>\n
\u624b\u52a8\u63d0\u793a\u7f16\u8bd1\u5668\u5206\u652f\u7684\u6267\u884c\u6982\u7387\u8981\u8c28\u614e\uff0c\u8fd9\u901a\u5e38\u6d89\u53ca\u5bf9\u5e94\u7528\u7a0b\u5e8f\u7684\u6df1\u5165\u4e86\u89e3\uff0c\u4ee5\u53ca\u5bf9\u6027\u80fd\u5f71\u54cd\u7684\u7ec6\u81f4\u5206\u6790\u3002<\/p>\n<\/p>\n
\u6d4b\u91cf\u4e0e\u8bc4\u4f30<\/strong>\uff1a\u4f60\u5e94\u8be5\u5148\u884c\u5bf9\u4ee3\u7801\u7684\u6027\u80fd\u8fdb\u884c\u7cbe\u786e\u6d4b\u91cf\uff0c\u7136\u540e\u518d\u51b3\u5b9a\u662f\u5426\u5b9e\u65bd\u5206\u652f\u9884\u6d4b\u4f18\u5316\u3002<\/p>\n<\/p>\n
\u5e73\u53f0\u7279\u5b9a<\/strong>\uff1a\u503c\u5f97\u6ce8\u610f\u7684\u662f\uff0c\u4e0d\u540c\u7684\u7f16\u8bd1\u5668\u548c\u76ee\u6807\u5e73\u53f0\u5bf9\u624b\u52a8\u5206\u652f\u9884\u6d4b\u7684\u652f\u6301\u7a0b\u5ea6\u4e0d\u540c\uff0c\u4f18\u5316\u6548\u679c\u53ef\u80fd\u4f1a\u6709\u663e\u8457\u5dee\u5f02\u3002<\/p>\n<\/p>\n
\u7efc\u4e0a\u6240\u8ff0\uff0c\u624b\u52a8\u4f18\u5316\u5206\u652f\u9884\u6d4b\u662f\u4e00\u4e2a\u9ad8\u7ea7\u6280\u672f\uff0c\u9700\u8981\u6df1\u5165\u7406\u89e3\u7a0b\u5e8f\u7684\u8fd0\u884c\u548c\u7f16\u8bd1\u5668\u7684\u5de5\u4f5c\u539f\u7406\uff0c\u624d\u80fd\u6b63\u786e\u5e76\u6709\u6548\u5730\u5e94\u7528\u3002\u4f7f\u7528__builtin_expect<\/code>\u6216C++20\u7684\u5c5e\u6027[[likely]]<\/code>\u548c[[unlikely]]<\/code>\u53ef\u4ee5\u663e\u8457\u63d0\u9ad8\u5173\u952e\u4ee3\u7801\u7684\u6027\u80fd\uff0c\u4f46\u5e94\u8c28\u614e\u4f7f\u7528\uff0c\u4ee5\u514d\u5f71\u54cd\u4ee3\u7801\u7684\u53ef\u8bfb\u6027\u548c\u53ef\u7ef4\u62a4\u6027\u3002\u5728\u591a\u6570\u60c5\u51b5\u4e0b\uff0c\u9075\u5faa\u7f16\u5199\u6e05\u6670\u3001\u903b\u8f91\u660e\u786e\u7684\u4ee3\u7801\u539f\u5219\uff0c\u5e76\u4f9d\u8d56\u73b0\u4ee3\u7f16\u8bd1\u5668\u7684\u4f18\u5316\u80fd\u529b\u662f\u66f4\u597d\u7684\u9009\u62e9\u3002<\/p>\n<\/p>\n
\u76f8\u5173\u95ee\u7b54FAQs\uff1a<\/strong><\/h2>\n
1. \u54ea\u4e9b\u65b9\u6cd5\u53ef\u4ee5\u5728 C \u4ee3\u7801\u4e2d\u6307\u793a\u7f16\u8bd1\u5668\u67d0\u4e2a\u5206\u652f\u7684\u6267\u884c\u6982\u7387\u8f83\u9ad8\uff1f<\/strong><\/p>\n
\u5728 C \u4ee3\u7801\u4e2d\uff0c\u53ef\u4ee5\u4f7f\u7528\u4ee5\u4e0b\u51e0\u79cd\u65b9\u6cd5\u6765\u6307\u793a\u7f16\u8bd1\u5668\u67d0\u4e2a\u5206\u652f\u7684\u6267\u884c\u6982\u7387\u8f83\u9ad8\uff1a<\/p>\n