{"id":1353,"date":"2018-06-07T23:07:33","date_gmt":"2018-06-07T15:07:33","guid":{"rendered":"https:\/\/damogame.cn:15443\/wordpress\/?p=1353"},"modified":"2018-06-07T23:07:33","modified_gmt":"2018-06-07T15:07:33","slug":"%e5%a4%9a%e9%87%8d%e7%bb%a7%e6%89%bf%e5%92%8c%e8%99%9a%e7%bb%a7%e6%89%bf%e7%9a%84%e5%86%85%e5%ad%98%e5%b8%83%e5%b1%80","status":"publish","type":"post","link":"https:\/\/i007.cc\/wordpress\/archives\/1353","title":{"rendered":"\u591a\u91cd\u7ee7\u627f\u548c\u865a\u7ee7\u627f\u7684\u5185\u5b58\u5e03\u5c40"},"content":{"rendered":"
\u591a\u91cd\u7ee7\u627f\u548c\u865a\u7ee7\u627f\u7684\u5185\u5b58\u5e03\u5c40<\/a><\/div>\n
<\/b>\u5206\u7c7b\uff1a\u00a0LINUX<\/p>\n

2011-09-08 12:55:50<\/p>\n<\/div>\n

\n
<\/div>\n
\n
\n

\u591a\u91cd\u7ee7\u627f\u548c\u865a\u7ee7\u627f\u7684\u5185\u5b58\u5e03\u5c40<\/strong><\/p>\n

\u523a\u732c@http:\/\/blog.csdn.net\/littlehedgehog<\/p>\n

 <\/p>\n

http:\/\/blog.csdn.net\/littlehedgehog\/article\/details\/5442430<\/a><\/p>\n

 <\/p>\n

\u8fd9\u7bc7\u6587\u7ae0\u4e3b\u8981\u8bb2\u89e3\u865a\u7ee7\u627f\u7684C++\u5bf9\u8c61\u5185\u5b58\u5206\u5e03\u95ee\u9898\uff0c\u4ece\u4e2d\u4e5f\u5f15\u51fa\u4e86dynamic_cast\u548cstatic_cast\u672c\u8d28\u533a\u522b\u3001\u865a\u51fd\u6570\u8868\u7684\u683c\u5f0f\u7b49\u4e00\u4e9b\u5927\u90e8\u5206C++\u7a0b\u5e8f\u5458\u90fd\u4f3c\u662f\u800c\u975e\u7684\u6982\u5ff5\u3002\u539f\u6587\u89c1\u8fd9\u91cc<\/a>(By Edsko de Vries, January 2006)<\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

\u00a0<\/span>\u656c\u544a:\u00a0\u672c\u6587\u662f\u4ecb\u7ecdC++\u7684\u6280\u672f\u6587\u7ae0\uff0c\u5047\u5b9a\u8bfb\u8005\u5bf9\u4e8eC++\u6709\u6bd4\u8f83\u6df1\u5165\u7684\u8ba4\u8bc6\uff0c\u540c\u65f6\u4e5f\u9700\u8981\u4e00\u4e9b\u6c47\u7f16\u77e5\u8bc6\u3002<\/p>\n

\u00a0\u00a0\u00a0\u672c\u6587\u6211\u4eec\u5c06\u9610\u91caGCC\u7f16\u8bd1\u5668\u9488\u5bf9\u591a\u91cd\u7ee7\u627f\u548c\u865a\u62df\u7ee7\u627f\u4e0b\u7684\u5bf9\u8c61\u5185\u5b58\u5e03\u5c40\u3002\u5c3d\u7ba1\u5728\u7406\u60f3\u7684\u4f7f\u7528\u73af\u5883\u4e2d\uff0c\u4e00\u4e2aC++\u7a0b\u5e8f\u5458\u5e76\u4e0d\u9700\u8981\u4e86\u89e3\u8fd9\u4e9b\u7f16\u8bd1\u5668\u5185\u90e8\u5b9e\u73b0\u7ec6\u8282\uff0c\u5b9e\u9645\u4e0a\uff0c\u7f16\u8bd1\u5668\u9488\u5bf9\u591a\u91cd\u7ee7\u627f(\u7279\u522b\u662f\u865a\u62df\u7ee7\u627f)\u7684\u5404\u79cd\u5b9e\u73b0\u7ec6\u8282\u5bf9\u4e8e\u6211\u4eec\u7f16\u5199C++\u4ee3\u7801\u90fd\u6216\u591a\u6216\u5c11\u4ea7\u751f\u4e00\u4e9b\u5f71\u54cd(\u6bd4\u5982downcasting\u00a0pointer\u3001pointers\u00a0to\u00a0pointers\u00a0\u4ee5\u53ca\u865a\u57fa\u7c7b\u6784\u9020\u51fd\u6570\u7684\u8c03\u7528\u987a\u5e8f)\u3002\u5982\u679c\u4f60\u80fd\u660e\u767d\u591a\u91cd\u7ee7\u627f\u662f\u5982\u4f55\u5b9e\u73b0\u7684\uff0c\u90a3\u4e48\u4f60\u81ea\u5df1\u5c31\u80fd\u591f\u9884\u89c1\u5230\u8fd9\u4e9b\u5f71\u54cd\uff0c\u8fdb\u800c\u80fd\u591f\u5728\u4f60\u7684\u4ee3\u7801\u4e2d\u5f88\u597d\u5730\u5e94\u5bf9\u5b83\u4eec\u3002\u518d\u8005\uff0c\u5982\u679c\u4f60\u5341\u5206\u5728\u610f\u7684\u4ee3\u7801\u7684\u8fd0\u884c\u6548\u7387\uff0c\u6b63\u786e\u5730\u7406\u89e3\u865a\u7ee7\u627f\u4e5f\u662f\u5f88\u6709\u5e2e\u52a9\u7684\u3002\u6700\u540e\u561b\uff0c\u8fd9\u4e2ahack\u7684\u8fc7\u7a0b\u662f\u5f88\u6709\u8da3\u7684\u54e6:)<\/p>\n

\n

\u591a\u91cd\u7ee7\u627f<\/strong><\/p>\n

\u00a0\u00a0 \u9996\u5148\u6211\u4eec\u5148\u6765\u8003\u8651\u4e00\u4e2a\u5f88\u7b80\u5355(non-virtual)\u7684\u591a\u91cd\u7ee7\u627f\u3002\u770b\u770b\u4e0b\u9762\u8fd9\u4e2aC++\u7c7b\u5c42\u6b21\u7ed3\u6784\u3002<\/p>\n

\u00a01\u00a0<\/span>class<\/strong>\u00a0Top
\n2\u00a0<\/span>{
\n3\u00a0<\/span>public<\/strong>:
\n4\u00a0<\/span>\u00a0\u00a0\u00a0<\/span>int<\/strong>\u00a0a;
\n5\u00a0<\/span>};
\n6\u00a0<\/span>
\n7\u00a0<\/span>class<\/strong>\u00a0Left :\u00a0<\/span>public<\/strong>\u00a0Top
\n8\u00a0<\/span>{
\n9\u00a0<\/span>public<\/strong>:
\n10\u00a0<\/span>\u00a0\u00a0\u00a0<\/span>int<\/strong>\u00a0b;
\n11\u00a0<\/span>};
\n12\u00a0<\/span>
\n13\u00a0<\/span>class<\/strong>\u00a0Right :\u00a0<\/span>public<\/strong>\u00a0Top
\n14\u00a0<\/span>{
\n15\u00a0<\/span>public<\/strong>:
\n16\u00a0<\/span>\u00a0\u00a0\u00a0<\/span>int<\/strong>\u00a0c;
\n17\u00a0<\/span>};
\n18\u00a0<\/span>
\n19\u00a0<\/span>class<\/strong>\u00a0Bottom :\u00a0<\/span>public<\/strong>\u00a0Left,\u00a0<\/span>public<\/strong>\u00a0Right
\n20\u00a0<\/span>{
\n21\u00a0<\/span>public<\/strong>:
\n22\u00a0<\/span>\u00a0\u00a0\u00a0<\/span>int<\/strong>\u00a0d;
\n23\u00a0<\/span>};
\n24\u00a0<\/span>
\n\u7528UML\u8868\u8ff0\u5982\u4e0b:<\/p>\n

\"\"<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u6ce8\u610f\u5230Top\u7c7b\u5b9e\u9645\u4e0a\u88ab\u7ee7\u627f\u4e86\u4e24\u6b21\uff0c(\u8fd9\u79cd\u673a\u5236\u5728Eiffel\u4e2d\u88ab\u79f0\u4f5crepeated\u00a0inheritance)\uff0c\u8fd9\u5c31\u610f\u5473\u7740\u5728\u4e00\u4e2abottom\u5bf9\u8c61\u4e2d\u5b9e\u9645\u4e0a\u6709\u4e24\u4e2aa\u5c5e\u6027(attributes\uff0c\u53ef\u4ee5\u901a\u8fc7bottom.Left::a\u548c\u00a0bottom.Right::a\u8bbf\u95ee)\u00a0\u3002<\/p>\n

\u00a0\u00a0\u00a0\u00a0<\/span>\u90a3\u4e48Left\u3001Right\u3001Bottom\u5728\u5185\u5b58\u4e2d\u5982\u4f55\u5206\u5e03\u7684\u5462\uff1f\u6211\u4eec\u5148\u6765\u770b\u770b\u7b80\u5355\u7684Left\u548cRight\u5185\u5b58\u5206\u5e03\uff1a<\/p>\n

\"\"<\/p>\n

[Right \u7c7b\u7684\u5e03\u5c40\u548cLeft\u662f\u4e00\u6837\u7684\uff0c\u56e0\u6b64\u6211\u8fd9\u91cc\u5c31\u6ca1\u518d\u753b\u56fe\u4e86\u3002\u523a\u732c]<\/p>\n

\u00a0<\/span>\u6ce8\u610f\u5230\u4e0a\u9762\u7c7b\u5404\u81ea\u7684\u7b2c\u4e00\u4e2a\u5c5e\u6027\u90fd\u662f\u7ee7\u627f\u81eaTop\u7c7b\uff0c\u8fd9\u5c31\u610f\u5473\u7740\u4e0b\u9762\u4e24\u4e2a\u8d4b\u503c\u8bed\u53e5:<\/p>\n

1\u00a0<\/span>Left* left =\u00a0<\/span>new<\/strong>\u00a0Left();
\n2\u00a0<\/span>Top* top = left;<\/p>\n

\u00a0<\/span>left\u548ctop\u5b9e\u9645\u4e0a\u662f\u6307\u5411\u4e24\u4e2a\u76f8\u540c\u7684\u5730\u5740\uff0c\u6211\u4eec\u53ef\u4ee5\u628aLeft\u5bf9\u8c61\u5f53\u4f5c\u4e00\u4e2aTop\u5bf9\u8c61(\u540c\u6837\u4e5f\u53ef\u4ee5\u628aRight\u5bf9\u8c61\u5f53Top\u5bf9\u8c61\u6765\u4f7f\u7528)\u3002\u4f46\u662fBotom\u5bf9\u8c61\u5462?GCC\u662f\u8fd9\u6837\u5904\u7406\u7684\uff1a<\/p>\n

\"\"<\/p>\n

\u00a0\u00a0\u00a0\u00a0 \u4f46\u662f\u73b0\u5728\u5982\u679c\u6211\u4eecupcast\u00a0\u4e00\u4e2aBottom\u6307\u9488\u5c06\u4f1a\u6709\u4ec0\u4e48\u7ed3\u679c?<\/p>\n

1\u00a0<\/span>Bottom* bottom =\u00a0<\/span>new<\/strong>\u00a0Bottom();
\n2\u00a0<\/span>Left* left = bottom;<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>\u8fd9\u6bb5\u4ee3\u7801\u8fd0\u884c\u6b63\u786e\u3002\u8fd9\u662f\u56e0\u4e3aGCC\u9009\u62e9\u7684\u8fd9\u79cd\u5185\u5b58\u5e03\u5c40\u4f7f\u5f97\u6211\u4eec\u53ef\u4ee5\u628aBottom\u5bf9\u8c61\u5f53\u4f5cLeft\u5bf9\u8c61\uff0c\u5b83\u4eec\u4e24\u8005(Left\u90e8\u5206)\u6b63\u597d\u76f8\u540c\u3002\u4f46\u662f\uff0c\u5982\u679c\u6211\u4eec\u628aBottom\u5bf9\u8c61\u6307\u9488upcast\u5230Right\u5bf9\u8c61\u5462?<\/p>\n

1\u00a0<\/span>Right* right = bottom;<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u5982\u679c\u6211\u4eec\u8981\u4f7f\u8fd9\u6bb5\u4ee3\u7801\u6b63\u5e38\u5de5\u4f5c\u7684\u8bdd\uff0c\u6211\u4eec\u9700\u8981\u8c03\u6574\u6307\u9488\u6307\u5411Bottom\u4e2d\u76f8\u5e94\u7684\u90e8\u5206\u3002<\/p>\n

\"\"<\/p>\n

\u00a0<\/span>\u901a\u8fc7\u8c03\u6574\uff0c\u6211\u4eec\u53ef\u4ee5\u7528right\u6307\u9488\u8bbf\u95eeBottom\u5bf9\u8c61\uff0c\u8fd9\u65f6Bottom\u5bf9\u8c61\u8868\u73b0\u5f97\u5c31\u5982Right\u5bf9\u8c61\u3002\u4f46\u662fbottom\u548cright\u6307\u9488\u6307\u5411\u4e86\u4e0d\u540c\u7684\u5185\u5b58\u5730\u5740\u3002\u6700\u540e\uff0c\u6211\u4eec\u8003\u8651\u4e0b:<\/p>\n

1\u00a0<\/span>Top* top = bottom;<\/p>\n

\u00a0<\/span>\u6069\uff0c\u4ec0\u4e48\u7ed3\u679c\u4e5f\u6ca1\u6709\uff0c\u8fd9\u6761\u8bed\u53e5\u5b9e\u9645\u4e0a\u662f\u6709\u6b67\u4e49(ambiguous)\u7684\uff0c\u7f16\u8bd1\u5668\u4f1a\u62a5\u9519: error: `Top’ is an ambiguous base of `Bottom’\u3002\u5176\u5b9e\u8fd9\u4e24\u79cd\u5e26\u6709\u6b67\u4e49\u7684\u53ef\u80fd\u6027\u53ef\u4ee5\u7528\u5982\u4e0b\u8bed\u53e5\u52a0\u4ee5\u533a\u5206\uff1a<\/p>\n

1\u00a0<\/span>Top* topL = (Left*) bottom;
\n2\u00a0<\/span>Top* topR = (Right*) bottom;\u00a0<\/span><\/p>\n

\u00a0<\/span>\u8fd9\u4e24\u4e2a\u8d4b\u503c\u8bed\u53e5\u6267\u884c\u4e4b\u540e\uff0ctopL\u548cleft\u6307\u9488\u5c06\u6307\u5411\u540c\u4e00\u4e2a\u5730\u5740\uff0c\u540c\u6837topR\u548cright<\/strong>\u4e5f\u5c06\u6307\u5411\u540c\u4e00\u4e2a\u5730\u5740<\/strong>\u3002<\/p>\n

 <\/p>\n

 <\/p>\n

\u865a\u62df\u7ee7\u627f<\/strong><\/p>\n

\u00a0<\/span>\u4e3a\u4e86\u907f\u514d\u4e0a\u8ff0Top\u7c7b\u7684\u591a\u6b21\u7ee7\u627f\uff0c\u6211\u4eec\u5fc5\u987b\u865a\u62df\u7ee7\u627f\u7c7bTop\u3002<\/p>\n

1\u00a0<\/span>class Top
\n2\u00a0<\/span>{
\n3\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0public<\/strong>:
\n4\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0int<\/strong>\u00a0a;
\n5\u00a0<\/span>};
\n6\u00a0<\/span>
\n7\u00a0<\/span>class Left : virtual public Top
\n8\u00a0<\/span>{
\n9\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0public<\/strong>:
\n10\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0int<\/strong>\u00a0b;
\n11\u00a0<\/span>};
\n12\u00a0<\/span>
\n13\u00a0<\/span>class Right : virtual public Top
\n14\u00a0<\/span>{
\n15\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0public<\/strong>:
\n16\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0int<\/strong>\u00a0c;
\n17\u00a0<\/span>};
\n18\u00a0<\/span>
\n19\u00a0<\/span>class Bottom : public Left, public Right
\n20\u00a0<\/span>{
\n21\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0public<\/strong>:
\n22\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0int<\/strong>\u00a0d;
\n23\u00a0<\/span>};
\n24<\/p>\n

\u00a0<\/span>\u4e0a\u8ff0\u4ee3\u7801\u5c06\u4ea7\u751f\u5982\u4e0b\u7684\u7c7b\u5c42\u6b21\u56fe(\u5176\u5b9e\u8fd9\u53ef\u80fd\u6b63\u597d\u662f\u4f60\u6700\u5f00\u59cb\u60f3\u8981\u7684\u7ee7\u627f\u65b9\u5f0f)\u3002<\/p>\n

\"virtualinheritance\"<\/p>\n

 <\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>\u5bf9\u4e8e\u7a0b\u5e8f\u5458\u6765\u8bf4\uff0c\u8fd9\u79cd\u7c7b\u5c42\u6b21\u56fe\u663e\u5f97\u66f4\u52a0\u7b80\u5355\u548c\u6e05\u6670\uff0c\u4e0d\u8fc7\u5bf9\u4e8e\u4e00\u4e2a\u7f16\u8bd1\u5668\u6765\u8bf4\uff0c\u8fd9\u5c31\u590d\u6742\u5f97\u591a\u4e86\u3002\u6211\u4eec\u518d\u7528Bottom\u7684\u5185\u5b58\u5e03\u5c40\u4f5c\u4e3a\u4f8b\u5b50\u8003\u8651\uff0c\u5b83\u53ef\u80fd\u662f\u8fd9\u6837\u7684:<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>\"\"<\/p>\n

\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>\u8fd9\u79cd\u5185\u5b58\u5e03\u5c40\u7684\u4f18\u52bf\u5728\u4e8e\u5b83\u7684\u5f00\u5934\u90e8\u5206(Left\u90e8\u5206)\u548cLeft\u7684\u5e03\u5c40\u6b63\u597d\u76f8\u540c\uff0c\u6211\u4eec\u53ef\u4ee5\u5f88\u8f7b\u6613\u5730\u901a\u8fc7\u4e00\u4e2aLeft\u6307\u9488\u8bbf\u95ee\u4e00\u4e2aBottom\u5bf9\u8c61\u3002\u4e0d\u8fc7\uff0c\u6211\u4eec\u518d\u6765\u8003\u8651\u8003\u8651Right:<\/p>\n

1\u00a0<\/span>Right* right = bottom;<\/p>\n

\u00a0\u00a0<\/span>\u8fd9\u91cc\u6211\u4eec\u5e94\u8be5\u628a\u4ec0\u4e48\u5730\u5740\u8d4b\u503c\u7ed9right\u6307\u9488\u5462\uff1f\u7406\u8bba\u4e0a\u8bf4\uff0c\u901a\u8fc7\u8fd9\u4e2a\u8d4b\u503c\u8bed\u53e5\uff0c\u6211\u4eec\u53ef\u4ee5\u628a\u8fd9\u4e2aright\u6307\u9488\u5f53\u4f5c\u771f\u6b63\u6307\u5411\u4e00\u4e2aRight\u5bf9\u8c61\u7684\u6307\u9488(\u73b0\u5728\u6307\u5411\u7684\u662fBottom)\u6765\u4f7f\u7528\u3002\u4f46\u5b9e\u9645\u4e0a\u8fd9\u662f\u4e0d\u73b0\u5b9e\u7684\uff01\u4e00\u4e2a\u771f\u6b63\u7684Right\u5bf9\u8c61\u5185\u5b58\u5e03\u5c40\u548cBottom\u5bf9\u8c61Right\u90e8\u5206\u662f\u5b8c\u5168\u4e0d\u540c\u7684\uff0c\u6240\u4ee5\u5176\u5b9e\u6211\u4eec\u4e0d\u53ef\u80fd\u518d\u628a\u8fd9\u4e2aupcasted\u7684bottom\u5bf9\u8c61\u5f53\u4f5c\u4e00\u4e2a\u771f\u6b63\u7684right\u5bf9\u8c61\u6765\u4f7f\u7528\u4e86\u3002\u800c\u4e14\uff0c\u6211\u4eec\u8fd9\u79cd\u5e03\u5c40\u7684\u8bbe\u8ba1\u4e0d\u53ef\u80fd\u8fd8\u6709\u6539\u8fdb\u7684\u4f59\u5730\u4e86\u3002\u8fd9\u91cc\u6211\u4eec\u5148\u770b\u770b\u5b9e\u9645\u4e0a\u5185\u5b58\u662f\u600e\u4e48\u5206\u5e03\u7684\uff0c\u7136\u540e\u518d\u89e3\u91ca\u4e0b\u4e3a\u4ec0\u4e48\u8fd9\u4e48\u8bbe\u8ba1\u3002<\/p>\n

\"vtable\"<\/p>\n

\u00a0<\/span>\u4e0a\u56fe\u6709\u4e24\u70b9\u503c\u5f97\u5927\u5bb6\u6ce8\u610f\u3002\u7b2c\u4e00\u70b9\u5c31\u662f\u7c7b\u4e2d\u6210\u5458\u5206\u5e03\u987a\u5e8f\u662f\u5b8c\u5168\u4e0d\u4e00\u6837\u7684(\u5b9e\u9645\u4e0a\u53ef\u4ee5\u8bf4\u662f\u6b63\u597d\u76f8\u53cd)\u3002\u7b2c\u4e8c\u70b9\uff0c\u7c7b\u4e2d\u589e\u52a0\u4e86vptr\u6307\u9488\uff0c\u8fd9\u4e9b\u662f\u88ab\u7f16\u8bd1\u5668\u5728\u7f16\u8bd1\u8fc7\u7a0b\u4e2d\u63d2\u5165\u5230\u7c7b\u4e2d\u7684(\u5728\u8bbe\u8ba1\u7c7b\u65f6\u5982\u679c\u4f7f\u7528\u4e86\u865a\u7ee7\u627f\uff0c\u865a\u51fd\u6570\u90fd\u4f1a\u4ea7\u751f\u76f8\u5173vptr)\u3002\u540c\u65f6\uff0c\u5728\u7c7b\u7684\u6784\u9020\u51fd\u6570\u4e2d\u4f1a\u5bf9\u76f8\u5173\u6307\u9488\u505a\u521d\u59cb\u5316\uff0c\u8fd9\u4e9b\u4e5f\u662f\u7f16\u8bd1\u5668\u5b8c\u6210\u7684\u5de5\u4f5c\u3002Vptr\u6307\u9488\u6307\u5411\u4e86\u4e00\u4e2a\u201cvirtual\u00a0table\u201d\u3002\u5728\u7c7b\u4e2d\u6bcf\u4e2a\u865a\u57fa\u7c7b\u90fd\u4f1a\u5b58\u5728\u4e0e\u4e4b\u5bf9\u5e94\u7684\u4e00\u4e2avptr\u6307\u9488\u3002\u4e3a\u4e86\u7ed9\u5927\u5bb6\u5c55\u793avirtual\u00a0table\u4f5c\u7528\uff0c\u8003\u8651\u4e0b\u5982\u4e0b\u4ee3\u7801\u3002<\/p>\n

1\u00a0<\/span>Bottom* bottom = new Bottom();
\n2\u00a0<\/span>Left* left = bottom;
\n3\u00a0<\/span>int<\/strong>\u00a0p = left->a;
\n\u00a0<\/span>\u7b2c\u4e8c\u6761\u7684\u8d4b\u503c\u8bed\u53e5\u8ba9left\u6307\u9488\u6307\u5411\u548cbottom\u540c\u6837\u7684\u8d77\u59cb\u5730\u5740(\u5373\u5b83\u6307\u5411Bottom\u5bf9\u8c61\u7684\u201c\u9876\u90e8\u201d)\u3002\u6211\u4eec\u6765\u8003\u8651\u4e0b\u7b2c\u4e09\u6761\u7684\u8d4b\u503c\u8bed\u53e5\u3002<\/p>\n

1\u00a0<\/span>movl\u00a0\u00a0left, %eax\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0# %eax\u00a0=\u00a0<\/span>left
\n2\u00a0<\/span>movl\u00a0\u00a0(%eax), %eax\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0# %eax\u00a0=\u00a0<\/span>left.vptr.Left<\/strong>
\n3\u00a0<\/span>movl\u00a0\u00a0(%eax), %eax\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0# %eax\u00a0=\u00a0<\/span>virtual\u00a0base\u00a0offset
\n4\u00a0<\/span>addl\u00a0\u00a0left, %eax\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0# %eax\u00a0=\u00a0<\/span>left\u00a0+\u00a0<\/span>virtual\u00a0base\u00a0offset
\n5\u00a0<\/span>movl\u00a0\u00a0(%eax), %eax\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0# %eax\u00a0=\u00a0<\/span>left.a
\n6\u00a0<\/span>movl\u00a0\u00a0%eax,\u00a0<\/span>p\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 #\u00a0<\/span>p\u00a0=\u00a0<\/span>left.a<\/p>\n

\u603b\u7ed3\u4e0b\uff0c\u6211\u4eec\u7528left\u6307\u9488\u53bb\u7d22\u5f15(\u627e\u5230)virtual\u00a0table\uff0c\u7136\u540e\u5728virtual\u00a0table\u4e2d\u83b7\u53d6<\/strong>\u5230\u865a\u57fa\u7c7b\u7684\u504f\u79fb(virtual\u00a0base\u00a0offset<\/strong>,\u00a0vbase)\uff0c\u7136\u540e\u5728left\u6307\u9488\u4e0a\u52a0\u4e0a\u8fd9\u4e2a\u504f\u79fb\u91cf\uff0c\u8fd9\u6837\u6211\u4eec\u5c31\u83b7\u53d6\u5230\u4e86Bottom\u7c7b\u4e2dTop<\/strong>\u7c7b\u7684\u5f00\u59cb\u5730\u5740\u3002<\/strong>\u4ece\u4e0a\u56fe\u4e2d\uff0c\u6211\u4eec\u53ef\u4ee5\u770b\u5230\u5bf9\u4e8eLeft\u6307\u9488\uff0c\u5b83\u7684virtual\u00a0base\u00a0offset\u662f20\uff0c\u5982\u679c\u6211\u4eec\u5047\u8bbeBottom\u4e2d\u6bcf\u4e2a\u6210\u5458\u90fd\u662f4\u5b57\u8282\u5927\u5c0f\uff0c\u90a3\u4e48Left\u6307\u9488\u52a0\u4e0a20\u5b57\u8282\u6b63\u597d\u662f\u6210\u5458a\u7684\u5730\u5740\u3002<\/p>\n

 <\/p>\n

\u00a0<\/span>\u6211\u4eec\u540c\u6837\u53ef\u4ee5\u7528\u76f8\u540c\u7684\u65b9\u5f0f\u8bbf\u95eeBottom\u4e2dRight\u90e8\u5206\u3002<\/p>\n

1\u00a0<\/span>Bottom* bottom = new Bottom();
\n2\u00a0<\/span>Right* right = bottom;
\n3\u00a0<\/span>int<\/strong>\u00a0p = right->a;<\/p>\n

\u00a0<\/span>right\u6307\u9488\u5c31\u4f1a\u6307\u5411\u5728Bottom\u5bf9\u8c61\u4e2d\u76f8\u5e94\u7684\u4f4d\u7f6e\u3002<\/p>\n

\"\"<\/p>\n

\u00a0<\/span>\u8fd9\u91cc\u5bf9\u4e8ep\u7684\u8d4b\u503c\u8bed\u53e5\u6700\u7ec8\u4f1a\u88ab\u7f16\u8bd1\u6210\u548c\u4e0a\u8ff0left\u76f8\u540c\u7684\u65b9\u5f0f\u8bbf\u95eea\u3002\u552f\u4e00\u7684\u4e0d\u540c\u662f\u5c31\u662fvptr\uff0c\u6211\u4eec\u8bbf\u95ee\u7684vptr\u73b0\u5728\u6307\u5411\u4e86virtual\u00a0table\u53e6\u4e00\u4e2a\u5730\u5740\uff0c\u6211\u4eec\u5f97\u5230\u7684virtual\u00a0base\u00a0offset\u4e5f\u53d8\u4e3a12\u3002\u6211\u4eec\u753b\u56fe\u603b\u7ed3\u4e0b\uff1a<\/p>\n

 <\/p>\n

\"virtualinheritance\"<\/p>\n

\u00a0<\/span>\u5f53\u7136\uff0c\u5173\u952e\u70b9\u5728\u4e8e\u6211\u4eec\u5e0c\u671b\u80fd\u591f\u8ba9\u8bbf\u95ee\u4e00\u4e2a\u771f\u6b63\u5355\u72ec\u7684Right\u5bf9\u8c61\u4e5f\u5982\u540c\u8bbf\u95ee\u4e00\u4e2a\u7ecf\u8fc7upcasted\uff08\u5230Right\u5bf9\u8c61\uff09\u7684Bottom\u5bf9\u8c61\u4e00\u6837\u3002\u8fd9\u91cc\u6211\u4eec\u4e5f\u5728Right\u5bf9\u8c61\u4e2d\u5f15\u5165vptrs\u3002<\/p>\n

\"vtable2\"<\/p>\n

\u00a0<\/span>OK\uff0c\u73b0\u5728\u8fd9\u6837\u7684\u8bbe\u8ba1\u7ec8\u4e8e\u8ba9\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u4e00\u4e2aRight\u6307\u9488\u8bbf\u95eeBottom\u5bf9\u8c61\u4e86\u3002\u4e0d\u8fc7\uff0c\u9700\u8981\u63d0\u9192\u7684\u662f\u4ee5\u4e0a\u8bbe\u8ba1\u9700\u8981\u627f\u62c5\u4e00\u4e2a\u76f8\u5f53\u5927\u7684\u4ee3\u4ef7\uff1a\u6211\u4eec\u9700\u8981\u5f15\u5165\u865a\u51fd\u6570\u8868\uff0c\u5bf9\u8c61\u5e95\u5c42\u4e5f\u5fc5\u987b\u6269\u5c55\u4ee5\u652f\u6301\u4e00\u4e2a\u6216\u591a\u4e2a\u865a\u51fd\u6570\u6307\u9488\uff0c\u539f\u6765\u4e00\u4e2a\u7b80\u5355\u7684\u6210\u5458\u8bbf\u95ee\u73b0\u5728\u9700\u8981\u901a\u8fc7\u865a\u51fd\u6570\u8868\u4e24\u6b21\u95f4\u63a5\u5bfb\u5740(\u7f16\u8bd1\u5668\u4f18\u5316\u53ef\u4ee5\u5728\u4e00\u5b9a\u7a0b\u5ea6\u4e0a\u51cf\u8f7b\u6027\u80fd\u635f\u5931)\u3002<\/p>\n

\n

Downcasting<\/strong><\/p>\n

\u00a0\u00a0\u00a0<\/span>\u5982\u6211\u4eec\u731c\u60f3\uff0c\u5c06\u4e00\u4e2a\u6307\u9488\u4ece\u4e00\u4e2a\u6d3e\u751f\u7c7b\u5230\u4e00\u4e2a\u57fa\u7c7b\u7684\u8f6c\u6362(casting)\u4f1a\u6d89\u53ca\u5230\u5728\u6307\u9488\u4e0a\u6dfb\u52a0\u504f\u79fb\u91cf\u3002\u53ef\u80fd\u6709\u670b\u53cb\u731c\u60f3\uff0cdowncasting\u4e00\u4e2a\u6307\u9488\u4ec5\u4ec5\u51cf\u53bb\u4e00\u4e9b\u504f\u79fb\u91cf\u5c31\u884c\u4e86\u5427\u3002\u5b9e\u9645\u4e0a\uff0c\u975e\u865a\u7ee7\u627f\u60c5\u51b5\u4e0b\u786e\u5b9e\u662f\u8fd9\u6837\uff0c\u4f46\u662f\uff0c\u5bf9\u4e8e\u865a\u7ee7\u627f\u6765\u8bf4\uff0c\u53c8\u4e0d\u5f97\u4e0d\u5f15\u5165\u5176\u5b83\u7684\u590d\u6742\u95ee\u9898\u3002\u8fd9\u91cc\u6211\u4eec\u5728\u4e0a\u9762\u7684\u4f8b\u5b50\u4e2d\u6dfb\u52a0\u4e00\u4e9b\u7ee7\u627f\u5173\u7cfb:<\/p>\n

1\u00a0<\/span>class AnotherBottom : public Left, public Right
\n2\u00a0<\/span>{
\n3\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0public<\/strong>:
\n4\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0int<\/strong>\u00a0e;
\n5\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0int<\/strong>\u00a0f;
\n6\u00a0<\/span>};<\/p>\n

 <\/p>\n

\u00a0\u00a0 \u8fd9\u4e2a\u7ee7\u627f\u5173\u7cfb\u5982\u4e0b\u56fe\u6240\u793a:<\/p>\n

\"virtual2\"<\/p>\n

\u00a0\u00a0 \u90a3\u4e48\u73b0\u5728\u8003\u8651\u5982\u4e0b\u4ee3\u7801<\/p>\n

1\u00a0<\/span>Bottom* bottom1 =\u00a0<\/span>new<\/strong>\u00a0Bottom();
\n2\u00a0<\/span>AnotherBottom* bottom2 =\u00a0<\/span>new<\/strong>\u00a0AnotherBottom();
\n3\u00a0<\/span>Top* top1 = bottom1;
\n4\u00a0<\/span>Top* top2 = bottom2;
\n5\u00a0<\/span>Left* left =\u00a0<\/span>static_cast<\/strong><left*>(top1);<\/left*>
\n\u4e0b\u9762\u8fd9\u56fe\u5c55\u793a\u4e86Bottom\u548cAnotherBottom\u7684\u5185\u5b58\u5e03\u5c40\uff0c\u540c\u65f6\u4e5f\u5c55\u793a\u4e86\u5404\u81eatop\u6307\u9488\u6240\u6307\u5411\u7684\u4f4d\u7f6e\u3002<\/p>\n

\"\"<\/p>\n

\u00a0<\/span>\u73b0\u5728\u6211\u4eec\u6765\u8003\u8651\u8003\u8651\u4ecetop1\u5230left\u7684static_cast\uff0c\u6ce8\u610f\u8fd9\u91cc\u6211\u4eec\u5e76\u4e0d\u6e05\u695a\u5bf9\u4e8etop1\u6307\u9488\u6307\u5411\u7684\u5bf9\u8c61\u662fBottom\u8fd8\u662fAnotherBottom\u3002\u8fd9\u91cc\u662f\u6839\u672c\u4e0d\u80fd\u7f16\u8bd1\u901a\u8fc7\u7684\uff01\u56e0\u4e3a\u6839\u672c\u4e0d\u80fd\u786e\u8ba4top1\u8fd0\u884c\u65f6\u9700\u8981\u8c03\u6574\u7684\u504f\u79fb\u91cf(\u5bf9\u4e8eBottom\u662f20\uff0c\u5bf9\u4e8eAnotherBottom\u662f24)\u3002\u6240\u4ee5\u7f16\u8bd1\u5668\u5c06\u4f1a\u63d0\u51fa\u9519\u8bef: error: cannot convert from base `Top’ to derived type `Left’ via virtual base `Top’\u3002\u8fd9\u91cc\u6211\u4eec\u9700\u8981\u77e5\u9053\u8fd0\u884c\u65f6\u4fe1\u606f\uff0c\u6240\u4ee5\u6211\u4eec\u9700\u8981\u4f7f\u7528dynamic_cast\uff1a<\/p>\n

1\u00a0<\/span>Left* left =\u00a0<\/span>dynamic_cast<\/strong><left*>(top1);<\/left*><\/p>\n

\u00a0\u00a0\u00a0\u00a0\u4e0d\u8fc7\uff0c\u7f16\u8bd1\u5668\u4ecd\u7136\u4f1a\u62a5\u9519\u7684\u00a0<\/span>error: cannot dynamic_cast `top’ (of type `class Top*’) to type `class Left*’ (source type is not polymorphic)\u3002\u5173\u952e\u95ee\u9898\u5728\u4e8e\u4f7f\u7528dynamic_cast\uff08\u548c\u4f7f\u7528typeid<\/strong>\u4e00\u6837\uff09\u9700\u8981\u77e5\u9053\u6307\u9488\u6240\u6307\u5bf9\u8c61\u7684\u8fd0\u884c\u65f6\u4fe1\u606f\u3002<\/strong>\u4f46\u662f\uff0c\u56de\u5934\u770b\u770b\u4e0a\u9762\u7684\u7ed3\u6784\u56fe\uff0c\u6211\u4eec\u5c31\u4f1a\u53d1\u73b0top1\u6307\u9488\u6240\u6307\u7684\u4ec5\u4ec5\u662f\u4e00\u4e2a\u6574\u6570\u6210\u5458a\u3002\u7f16\u8bd1\u5668\u6ca1\u6709\u5728Bottom\u7c7b\u4e2d\u5305\u542b\u9488\u5bf9top\u7684vptr\uff0c\u5b83\u8ba4\u4e3a\u8fd9\u5b8c\u5168\u6ca1\u6709\u5fc5\u8981\u3002\u4e3a\u4e86\u5f3a\u5236\u7f16\u8bd1\u5668\u5728Bottom\u4e2d\u5305\u542btop\u7684vptr\uff0c\u6211\u4eec\u53ef\u4ee5\u5728top\u7c7b\u91cc\u9762\u6dfb\u52a0\u4e00\u4e2a\u865a\u6790\u6784\u51fd\u6570\u3002<\/p>\n

1\u00a0<\/span>class<\/strong>\u00a0Top
\n2\u00a0<\/span>{
\n3\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0public<\/strong>:
\n4\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0virtual<\/strong>\u00a0~Top() {}\u00a0<\/span>
\n5\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0int<\/strong>\u00a0a;
\n6\u00a0<\/span>};<\/p>\n

 <\/p>\n

\u00a0\u00a0\u00a0\u00a0\u8fd9\u5c31\u8feb\u4f7f\u7f16\u8bd1\u5668\u4e3aTop\u7c7b\u6dfb\u52a0\u4e86\u4e00\u4e2avptr\u3002\u4e0b\u9762\u6765\u770b\u770bBottom\u65b0\u7684\u5185\u5b58\u5e03\u5c40\uff1a<\/p>\n

\"\"<\/p>\n

\u00a0\u00a0 \u662f\u7684\uff0c\u5176\u5b83\u6d3e\u751f\u7c7b(Left\u3001Right)\u90fd\u4f1a\u6dfb\u52a0\u4e00\u4e2avptr.top\uff0c\u7f16\u8bd1\u5668\u4e3adynamic_cast\u751f\u6210\u4e86\u4e00\u4e2a\u5e93\u51fd\u6570\u8c03\u7528\u3002<\/p>\n

1\u00a0<\/span>left = __dynamic_cast(top1, typeinfo_for_Top, typeinfo_for_Left, -1);<\/p>\n

\u00a0\u00a0 __dynamic_cast\u5b9a\u4e49\u5728libstdc++(\u5bf9\u5e94\u7684\u5934\u6587\u4ef6\u662fcxxabi.h)\uff0c\u6709\u4e86Top\u3001Left\u548cBottom\u7684\u7c7b\u578b\u4fe1\u606f\uff0c\u8f6c\u6362\u5f97\u4ee5\u6267\u884c\u3002\u5176\u4e2d\uff0c\u53c2\u6570-1\u4ee3\u8868\u7684\u662f\u7c7bLeft\u548c\u7c7bTop\u4e4b\u95f4\u7684\u5173\u7cfb\u672a\u660e\u3002\u5982\u679c\u60f3\u8be6\u7ec6\u4e86\u89e3\uff0c\u8bf7\u53c2\u770btinfo.cc<\/a>\u7684\u5b9e\u73b0\u3002<\/p>\n

 <\/p>\n

 <\/p>\n

\n

\u603b\u7ed3<\/strong><\/p>\n

\u00a0\u00a0\u00a0\u00a0<\/span>\u6700\u540e\uff0c\u6211\u4eec\u518d\u804a\u804a\u4e00\u4e9b\u76f8\u5173\u5185\u5bb9\u3002<\/p>\n

\n

\u4e8c\u7ea7\u6307\u9488<\/strong><\/p>\n

\u00a0\u00a0\u00a0\u8fd9\u91cc\u7684\u95ee\u9898\u521d\u770b\u6478\u4e0d\u7740\u5934\u8111\uff0c\u4f46\u662f\u7ec6\u7ec6\u60f3\u6765\u6709\u4e9b\u95ee\u9898\u8fd8\u662f\u663e\u800c\u6613\u89c1\u7684\u3002\u8fd9\u91cc\u6211\u4eec\u8003\u8651\u4e00\u4e2a\u95ee\u9898\uff0c\u8fd8\u662f\u4ee5\u4e0a\u8282\u7684Downcasting\u4e2d\u7684\u7c7b\u7ee7\u627f\u7ed3\u6784\u56fe\u4f5c\u4e3a\u4f8b\u5b50\u3002<\/p>\n

1\u00a0<\/span>Bottom* b =\u00a0<\/span>new<\/strong>\u00a0Bottom();
\n2\u00a0<\/span>Right* r = b;<\/p>\n

(\u5728\u628ab\u6307\u9488\u7684\u503c\u8d4b\u503c\u7ed9\u6307\u9488r\u65f6\uff0cb\u6307\u9488\u5c06\u52a0\u4e0a8\u5b57\u8282\uff0c\u8fd9\u6837r\u6307\u9488\u624d\u6307\u5411Bottom\u5bf9\u8c61\u4e2dRight\u90e8\u5206)\u3002\u56e0\u6b64\u6211\u4eec\u53ef\u4ee5\u628aBottom*\u7c7b\u578b\u7684\u503c\u8d4b\u503c\u7ed9Right*\u5bf9\u8c61\u3002\u4f46\u662fBottom**\u548cRight**\u4e24\u79cd\u7c7b\u578b\u7684\u6307\u9488\u4e4b\u95f4\u8d4b\u503c\u5462\uff1f<\/p>\n

1\u00a0<\/span>Bottom** bb = &b;
\n2\u00a0<\/span>Right** rr = bb;<\/p>\n

\u7f16\u8bd1\u5668\u80fd\u901a\u8fc7\u8fd9\u4e24\u6761\u8bed\u53e5\u5417\uff1f\u5b9e\u9645\u4e0a\u7f16\u8bd1\u5668\u4f1a\u62a5\u9519: error: invalid conversion from `Bottom**’ to `Right**’
\n\u00a0<\/span>\u4e3a\u4ec0\u4e48?\u00a0\u4e0d\u59a8\u53cd\u8fc7\u6765\u60f3\u60f3\uff0c\u5982\u679c\u80fd\u591f\u5c06bb\u8d4b\u503c\u7ed9rr\uff0c\u5982\u4e0b\u56fe\u6240\u793a\u3002\u6240\u4ee5\u8fd9\u91ccbb\u548crr\u4e24\u4e2a\u6307\u9488\u90fd\u6307\u5411\u4e86b\uff0cb\u548cr\u90fd\u6307\u5411\u4e86Bottom\u5bf9\u8c61\u7684\u76f8\u5e94\u90e8\u5206\u3002\u90a3\u4e48\u73b0\u5728\u8003\u8651\u8003\u8651\u5982\u679c\u7ed9*rr\u8d4b\u503c\u5c06\u4f1a\u53d1\u751f\u4ec0\u4e48\u3002<\/p>\n

1\u00a0<\/span>*rr = b;<\/p>\n

\u6ce8\u610f*rr\u662fRight*\u7c7b\u578b(\u4e00\u7ea7)\u7684\u6307\u9488\uff0c\u6240\u4ee5\u8fd9\u4e2a\u8d4b\u503c\u662f\u6709\u6548\u7684\uff01<\/p>\n

\"doublepointers\"<\/p>\n

\u00a0\u00a0\u00a0 \u8fd9\u4e2a\u5c31\u548c\u6211\u4eec\u4e0a\u9762\u7ed9r\u6307\u9488\u8d4b\u503c\u4e00\u6837(*rr\u662f\u4e00\u7ea7\u7684Right*\u7c7b\u578b\u6307\u9488\uff0c\u800cr\u540c\u6837\u662f\u4e00\u7ea7Right*\u6307\u9488)\u3002\u6240\u4ee5\uff0c\u7f16\u8bd1\u5668\u5c06\u91c7\u7528\u76f8\u540c\u7684\u65b9\u5f0f\u5b9e\u73b0\u5bf9*rr\u7684\u8d4b\u503c\u64cd\u4f5c\u3002\u5b9e\u9645\u4e0a\uff0c\u6211\u4eec\u53c8\u8981\u8c03\u6574b\u7684\u503c\uff0c\u52a0\u4e0a8\u5b57\u8282\uff0c\u7136\u540e\u8d4b\u503c\u7ed9*rr\uff0c\u4f46\u662f\u73b0\u5728**rr\u5176\u5b9e\u662f\u6307\u5411b\u7684!\u5982\u4e0b\u56fe<\/p>\n

\"\"<\/p>\n

\u5443\uff0c\u5982\u679c\u6211\u4eec\u901a\u8fc7rr\u8bbf\u95eeBottom\u5bf9\u8c61\uff0c\u90a3\u4e48\u6309\u7167\u4e0a\u56fe\u7ed3\u6784\u6211\u4eec\u80fd\u591f\u5b8c\u6210\u5bf9Bottom\u5bf9\u8c61\u7684\u8bbf\u95ee\uff0c\u4f46\u662f\u5982\u679c\u662f\u7528b\u6765\u8bbf\u95eeBottom\u5bf9\u8c61\u5462\uff0c\u6240\u6709\u7684\u5bf9\u8c61\u5f15\u7528\u5b9e\u9645\u4e0a\u90fd\u504f\u79fb\u4e868\u5b57\u8282\u2014\u2014\u660e\u663e\u662f\u9519\u8bef\u7684\uff01<\/p>\n

\u00a0\u00a0 \u603b\u800c\u8a00\u4e4b\uff0c\u5c3d\u7ba1*a\u548c*b\u4e4b\u95f4\u80fd\u4f9d\u9760\u7c7b\u7ee7\u627f\u5173\u7cfb\u76f8\u4e92\u8f6c\u5316\uff0c\u800c**a\u548c**b\u4e0d\u80fd\u6709\u8fd9\u79cd\u63a8\u8bba\u3002<\/p>\n

 <\/p>\n

\u865a\u57fa\u7c7b\u7684\u6784\u9020\u51fd\u6570<\/strong><\/p>\n

\u00a0\u00a0 \u7f16\u8bd1\u5668\u5fc5\u987b\u8981\u4fdd\u8bc1\u6240\u6709\u7684\u865a\u51fd\u6570\u6307\u9488\u8981\u88ab\u6b63\u786e\u7684\u521d\u59cb\u5316\u3002\u7279\u522b\u662f\u8981\u4fdd\u8bc1\u7c7b\u4e2d\u6240\u6709\u865a\u57fa\u7c7b\u7684\u6784\u9020\u51fd\u6570\u90fd\u8981\u88ab\u8c03\u7528\uff0c\u800c\u4e14\u8fd8\u53ea\u80fd\u8c03\u7528\u4e00\u6b21\u3002<\/strong>\u5982\u679c\u4f60\u5199\u4ee3\u7801\u65f6\u81ea\u5df1\u4e0d\u663e\u793a\u8c03\u7528\u6784\u9020\u51fd\u6570\uff0c\u7f16\u8bd1\u5668\u4f1a\u81ea\u52a8\u63d2\u5165\u4e00\u6bb5\u6784\u9020\u51fd\u6570\u8c03\u7528\u4ee3\u7801\u3002\u8fd9\u5c06\u4f1a\u5bfc\u81f4\u4e00\u4e9b\u5947\u602a\u7684\u7ed3\u679c\uff0c\u540c\u6837\u8003\u8651\u4e0b\u4e0a\u9762\u7684\u7c7b\u7ee7\u627f\u7ed3\u6784\u56fe\uff0c\u4e0d\u8fc7\u8981\u52a0\u5165\u6784\u9020\u51fd\u6570\u3002<\/p>\n

\u00a01\u00a0<\/span>class<\/strong>\u00a0Top
\n2\u00a0<\/span>{
\n3\u00a0<\/span>public<\/strong>:
\n4\u00a0<\/span>\u00a0\u00a0 Top() { a = -1; }\u00a0<\/span>
\n5\u00a0<\/span>\u00a0\u00a0 Top(int<\/strong>\u00a0_a) { a = _a; }\u00a0<\/span>
\n6\u00a0<\/span>\u00a0\u00a0\u00a0<\/span>int<\/strong>\u00a0a;
\n7\u00a0<\/span>};
\n8\u00a0<\/span>
\n9\u00a0<\/span>class<\/strong>\u00a0Left :\u00a0<\/span>public<\/strong>\u00a0Top
\n10\u00a0<\/span>{
\n11\u00a0<\/span>public<\/strong>:
\n12\u00a0<\/span>\u00a0\u00a0 Left() { b = -2; }
\n13\u00a0<\/span>\u00a0\u00a0 Left(int<\/strong>\u00a0_a,\u00a0<\/span>int<\/strong>\u00a0_b) : Top(_a) { b = _b; }
\n14\u00a0<\/span>\u00a0\u00a0\u00a0<\/span>int<\/strong>\u00a0b;
\n15\u00a0<\/span>};
\n16\u00a0<\/span>
\n17\u00a0<\/span>class<\/strong>\u00a0Right :\u00a0<\/span>public<\/strong>\u00a0Top
\n18\u00a0<\/span>{
\n19\u00a0<\/span>public<\/strong>:
\n20\u00a0<\/span>\u00a0\u00a0 Right() { c = -3; }
\n21\u00a0<\/span>\u00a0\u00a0 Right(int<\/strong>\u00a0_a,\u00a0<\/span>int<\/strong>\u00a0_c) : Top(_a) { c = _c; }
\n22\u00a0<\/span>\u00a0\u00a0\u00a0<\/span>int<\/strong>\u00a0c;
\n23\u00a0<\/span>};
\n24\u00a0<\/span>
\n25\u00a0<\/span>class<\/strong>\u00a0Bottom :\u00a0<\/span>public<\/strong>\u00a0Left,\u00a0<\/span>public<\/strong>\u00a0Right
\n26\u00a0<\/span>{
\n27\u00a0<\/span>public<\/strong>:
\n28\u00a0<\/span>\u00a0\u00a0 Bottom() { d = -4; }\u00a0<\/span>
\n29\u00a0<\/span>\u00a0\u00a0 Bottom(int<\/strong>\u00a0_a,\u00a0<\/span>int<\/strong>\u00a0_b,\u00a0<\/span>int<\/strong>\u00a0_c,\u00a0<\/span>int<\/strong>\u00a0_d) : Left(_a, _b), Right(_a, _c)\u00a0<\/span>
\n30\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0{\u00a0<\/span>
\n31\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0d = _d;\u00a0<\/span>
\n32\u00a0<\/span>\u00a0\u00a0\u00a0\u00a0}
\n33\u00a0<\/span>\u00a0\u00a0\u00a0<\/span>int<\/strong>\u00a0d;
\n34\u00a0<\/span>};
\n35
\n\u5148\u6765\u8003\u8651\u4e0b\u4e0d\u5305\u542b\u865a\u51fd\u6570\u7684\u60c5\u51b5\uff0c\u4e0b\u9762\u8fd9\u6bb5\u4ee3\u7801\u8f93\u51fa\u4ec0\u4e48?<\/p>\n

1\u00a0<\/span>Bottom bottom(1,2,3,4);
\n2\u00a0<\/span>printf(“%d\u00a0%d\u00a0%d\u00a0%d\u00a0%d\/n”, bottom.Left::a, bottom.Right::a, bottom.b, bottom.c, bottom.d);
\n\u00a0<\/span>\u4f60\u53ef\u80fd\u731c\u60f3\u4f1a\u6709\u8fd9\u6837\u7ed3\u679c\uff1a<\/p>\n

1 1 2 3 4
\n\u00a0<\/span>\u4f46\u662f\uff0c\u5982\u679c\u6211\u4eec\u8003\u8651\u4e0b\u5305\u542b\u865a\u51fd\u6570\u7684\u60c5\u51b5\u5462\uff0c\u5982\u679c\u6211\u4eec\u4eceTop\u865a\u7ee7\u627f\u6d3e\u751f\u51fa\u5b50\u7c7b\uff0c\u90a3\u4e48\u6211\u4eec\u5c06\u5f97\u5230\u5982\u4e0b\u7ed3\u679c\uff1a<\/p>\n

 <\/p>\n

-1 -1 2 3 4
\n\u00a0<\/span>\u5982\u672c\u8282\u5f00\u5934\u6240\u8bb2\uff0c\u7f16\u8bd1\u5668\u5728Bottom\u4e2d\u63d2\u5165\u4e86\u4e00\u4e2aTop\u7684\u9ed8\u8ba4\u6784\u9020\u51fd\u6570\uff0c\u800c\u4e14\u8fd9\u4e2a\u9ed8\u8ba4\u6784\u9020\u51fd\u6570\u5b89\u6392\u5728\u5176\u4ed6\u7684\u6784\u9020\u51fd\u6570\u4e4b\u524d\uff0c\u5f53Left\u5f00\u59cb\u8c03\u7528\u5b83\u7684\u57fa\u7c7b\u6784\u9020\u51fd\u6570\u65f6\uff0c\u6211\u4eec\u53d1\u73b0Top\u5df2\u7ecf\u6784\u9020\u521d\u59cb\u5316\u597d\u4e86\uff0c\u6240\u4ee5\u76f8\u5e94\u7684\u6784\u9020\u51fd\u6570\u4e0d\u4f1a\u88ab\u8c03\u7528\u3002\u5982\u679c\u8ddf\u8e2a\u6784\u9020\u51fd\u6570\uff0c\u6211\u4eec\u5c06\u4f1a\u770b\u5230<\/p>\n

Top::Top()
\nLeft::Left(1,2)
\nRight::Right(1,3)
\nBottom::Bottom(1,2,3,4)
\n\u4e3a\u4e86\u907f\u514d\u8fd9\u79cd\u60c5\u51b5\uff0c\u6211\u4eec\u5e94\u8be5\u663e\u793a\u5730\u8c03\u7528\u865a\u57fa\u7c7b\u7684\u6784\u9020\u51fd\u6570<\/p>\n

1\u00a0<\/span>Bottom(int<\/strong>\u00a0_a,\u00a0<\/span>int<\/strong>\u00a0_b,\u00a0<\/span>int<\/strong>\u00a0_c,\u00a0<\/span>int<\/strong>\u00a0_d): Top(_a), Left(_a,_b), Right(_a,_c)\u00a0<\/span>
\n2\u00a0<\/span>{\u00a0<\/span>
\n3\u00a0<\/span>\u00a0\u00a0 d = _d;\u00a0<\/span>
\n4\u00a0<\/span>}<\/p>\n

\n

\u5230void*\u00a0\u7684\u8f6c\u6362<\/strong><\/p>\n

\u00a01\u00a0<\/span>dynamic_cast<\/strong><void<\/strong>*>(b);<\/p>\n

\u00a0<\/span>\u6700\u540e\u6211\u4eec\u6765\u8003\u8651\u4e0b\u628a\u4e00\u4e2a\u6307\u9488\u8f6c\u6362\u5230void\u00a0*\u3002\u7f16\u8bd1\u5668\u4f1a\u628a\u6307\u9488\u8c03\u6574\u5230\u5bf9\u8c61\u7684\u5f00\u59cb\u5730\u5740\u3002\u901a\u8fc7\u67e5vtable\uff0c\u8fd9\u4e2a\u5e94\u8be5\u662f\u5f88\u5bb9\u6613\u5b9e\u73b0\u3002\u770b\u770b\u4e0a\u9762\u7684vtable\u7ed3\u6784\u56fe\uff0c\u5176\u4e2doffset\u00a0to\u00a0top\u5c31\u662fvptr\u5230\u5bf9\u8c61\u5f00\u59cb\u5730\u5740\u3002\u53e6\u5916\u56e0\u4e3a\u8981\u67e5\u9605vtable\uff0c\u6240\u4ee5\u9700\u8981\u4f7f\u7528dynamic_cast\u3002<\/p>\n

\u6307\u9488\u7684\u6bd4\u8f83<\/strong><\/p>\n

\u00a0\u00a0 \u518d\u4ee5\u4e0a\u9762Bottom\u7c7b\u7ee7\u627f\u5173\u7cfb\u4e3a\u4f8b\u8ba8\u8bba\uff0c\u4e0b\u9762\u8fd9\u6bb5\u4ee3\u7801\u4f1a\u6253\u5370Equal\u5417\uff1f<\/p>\n

1\u00a0<\/span>Bottom* b =\u00a0<\/span>new<\/strong>\u00a0Bottom();\u00a0<\/span>
\n2\u00a0<\/span>Right* r = b;
\n3\u00a0<\/span>
\n4\u00a0<\/span>if<\/strong>(r == b)
\n5\u00a0<\/span>\u00a0\u00a0 printf(“Equal!\/n”);
\n\u00a0\u5148\u660e\u786e\u4e0b\u8fd9\u4e24\u4e2a\u6307\u9488\u5b9e\u9645\u4e0a\u662f\u6307\u5411\u4e0d\u540c\u5730\u5740\u7684\uff0cr\u6307\u9488\u5b9e\u9645\u4e0a\u5728b\u6307\u9488\u6240\u6307\u5730\u5740\u4e0a\u504f\u79fb8\u5b57\u8282<\/strong>\uff0c\u4f46\u662f\uff0c\u8fd9\u4e9bC++\u5185\u90e8\u7ec6\u8282\u4e0d\u80fd\u544a\u8bc9C++\u7a0b\u5e8f\u5458\uff0c\u6240\u4ee5C++\u7f16\u8bd1\u5668\u5728\u6bd4\u8f83r\u548cb\u65f6\uff0c\u4f1a\u628ar\u51cf\u53bb8\u5b57\u8282\uff0c\u7136\u540e\u518d\u6765\u6bd4\u8f83\uff0c\u6240\u4ee5\u6253\u5370\u51fa\u7684\u503c\u662f”Equal”.<\/p>\n

\n

\u53c2\u8003\u6587\u732e<\/strong><\/p>\n

 <\/p>\n

[1]\u00a0<\/span>CodeSourcery<\/a>, in particular the\u00a0<\/span>C++ ABI Summary<\/a>, the\u00a0<\/span>Itanium C++ ABI<\/a>\u00a0<\/span>(despite the name, this document is referenced in a platform-independent context; in particular, the\u00a0<\/span>structure of the vtables<\/a>\u00a0<\/span>is detailed here). The\u00a0<\/span>libstdc++\u00a0<\/span>implementation of dynamic casts, as well RTTI and name unmangling\/demangling, is defined in\u00a0<\/span>tinfo.cc<\/a>.<\/p>\n

[2] The\u00a0<\/span>libstdc++<\/a>\u00a0<\/span>website, in particular the section on the\u00a0<\/span>C++ Standard Library API<\/a>.<\/p>\n

[3]\u00a0<\/span>C++: Under the Hood<\/a>\u00a0<\/span>by Jan Gray.<\/p>\n

[4] Chapter 9, \u201cMultiple Inheritance\u201d of\u00a0<\/span>Thinking in C++ (volume 2)<\/em>\u00a0<\/span>by\u00a0<\/span>Bruce Eckel<\/a>. The author has made this book available fordownload<\/a>.<\/p>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

\u591a\u91cd\u7ee7\u627f\u548c\u865a\u7ee7\u627f\u7684\u5185\u5b58\u5e03\u5c40 \u5206\u7c7b\uff1a\u00a0LI<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"colormag_page_container_layout":"default_layout","colormag_page_sidebar_layout":"default_layout","footnotes":""},"categories":[],"tags":[118],"class_list":["post-1353","post","type-post","status-publish","format-standard","hentry","tag-02-"],"_links":{"self":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts\/1353","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/comments?post=1353"}],"version-history":[{"count":0,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts\/1353\/revisions"}],"wp:attachment":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/media?parent=1353"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/categories?post=1353"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/tags?post=1353"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}