{"id":5298,"date":"2021-06-06T03:24:02","date_gmt":"2021-06-05T19:24:02","guid":{"rendered":"https:\/\/damogame.cn\/wordpress\/?p=5298"},"modified":"2021-06-06T03:24:02","modified_gmt":"2021-06-05T19:24:02","slug":"c%e8%af%ad%e8%a8%800%e9%95%bf%e5%ba%a6%e6%95%b0%e7%bb%84%e5%8f%af%e5%8f%98%e6%95%b0%e7%bb%84-%e6%9f%94%e6%80%a7%e6%95%b0%e7%bb%84%e8%af%a6%e8%a7%a3","status":"publish","type":"post","link":"https:\/\/i007.cc\/wordpress\/archives\/5298","title":{"rendered":"C\u8bed\u8a000\u957f\u5ea6\u6570\u7ec4(\u53ef\u53d8\u6570\u7ec4\/\u67d4\u6027\u6570\u7ec4)\u8be6\u89e3"},"content":{"rendered":"

\u539f\u6587\u5730\u5740<\/a><\/p>\n

 <\/p>\n

CHENG Jian 2017-03-20 19:37:26 31665 \u6536\u85cf 132
\n\u5206\u7c7b\u4e13\u680f\uff1a \u2508\u2508\u3010C \/ C++\u53d1\u73b0\u3011 \u6587\u7ae0\u6807\u7b7e\uff1a c\u8bed\u8a00 \u53d8\u957f\u6570\u7ec4 0\u957f\u5ea6\u6570\u7ec4 C\u6269\u5c55 GNU
\n\u7248\u6743
\nCSDN GitHub
\nC\u8bed\u8a000\u957f\u5ea6\u6570\u7ec4(\u53ef\u53d8\u6570\u7ec4\/\u67d4\u6027\u6570\u7ec4)\u8be6\u89e3 AderXCoding\/language\/c\/zero_length_array<\/p>\n

\u672c\u4f5c\u54c1\u91c7\u7528\u77e5\u8bc6\u5171\u4eab\u7f72\u540d-\u975e\u5546\u4e1a\u6027\u4f7f\u7528-\u76f8\u540c\u65b9\u5f0f\u5171\u4eab 4.0 \u56fd\u9645\u8bb8\u53ef\u534f\u8bae\u8fdb\u884c\u8bb8\u53ef, \u8f6c\u8f7d\u8bf7\u6ce8\u660e\u51fa\u5904, \u8c22\u8c22\u5408\u4f5c<\/p>\n

1 \u96f6\u957f\u5ea6\u6570\u7ec4\u6982\u5ff5
\n\u4f17\u6240\u5468\u77e5, GNU\/GCC \u5728\u6807\u51c6\u7684 C\/C++ \u57fa\u7840\u4e0a\u505a\u4e86\u6709\u5b9e\u7528\u6027\u7684\u6269\u5c55, \u96f6\u957f\u5ea6\u6570\u7ec4\uff08Arrays of Length Zero\uff09 \u5c31\u662f\u5176\u4e2d\u4e00\u4e2a\u77e5\u540d\u7684\u6269\u5c55.<\/p>\n

\u591a\u6570\u60c5\u51b5\u4e0b, \u5176\u5e94\u7528\u5728\u53d8\u957f\u6570\u7ec4\u4e2d, \u5176\u5b9a\u4e49\u5982\u4e0b<\/p>\n

struct Packet
\n{
\nint state;
\nint len;
\nchar cData[0]; \/\/\u8fd9\u91cc\u76840\u957f\u7ed3\u6784\u4f53\u5c31\u4e3a\u53d8\u957f\u7ed3\u6784\u4f53\u63d0\u4f9b\u4e86\u975e\u5e38\u597d\u7684\u652f\u6301
\n};
\n1
\n2
\n3
\n4
\n5
\n6
\n\u9996\u5148\u5bf9 0\u957f\u5ea6\u6570\u7ec4, \u4e5f\u53eb\u67d4\u6027\u6570\u7ec4 \u505a\u4e00\u4e2a\u89e3\u91ca \uff1a<\/p>\n

\u7528\u9014 : \u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4\u7684\u4e3b\u8981\u7528\u9014\u662f\u4e3a\u4e86\u6ee1\u8db3\u9700\u8981\u53d8\u957f\u5ea6\u7684\u7ed3\u6784\u4f53<\/p>\n

\u7528\u6cd5 : \u5728\u4e00\u4e2a\u7ed3\u6784\u4f53\u7684\u6700\u540e, \u7533\u660e\u4e00\u4e2a\u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4, \u5c31\u53ef\u4ee5\u4f7f\u5f97\u8fd9\u4e2a\u7ed3\u6784\u4f53\u662f\u53ef\u53d8\u957f\u7684. \u5bf9\u4e8e\u7f16\u8bd1\u5668\u6765\u8bf4, \u6b64\u65f6\u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4\u5e76\u4e0d\u5360\u7528\u7a7a\u95f4, \u56e0\u4e3a\u6570\u7ec4\u540d\u672c\u8eab\u4e0d\u5360\u7a7a\u95f4, \u5b83\u53ea\u662f\u4e00\u4e2a\u504f\u79fb\u91cf, \u6570\u7ec4\u540d\u8fd9\u4e2a\u7b26\u53f7\u672c\u8eab\u4ee3\u8868\u4e86\u4e00\u4e2a\u4e0d\u53ef\u4fee\u6539\u7684\u5730\u5740\u5e38\u91cf<\/p>\n

(\u6ce8\u610f : \u6570\u7ec4\u540d\u6c38\u8fdc\u90fd\u4e0d\u4f1a\u662f\u6307\u9488!), \u4f46\u5bf9\u4e8e\u8fd9\u4e2a\u6570\u7ec4\u7684\u5927\u5c0f, \u6211\u4eec\u53ef\u4ee5\u8fdb\u884c\u52a8\u6001\u5206\u914d<\/p>\n

\u6ce8\u610f \uff1a\u5982\u679c\u7ed3\u6784\u4f53\u662f\u901a\u8fc7calloc\u3001malloc\u6216 \u8005new\u7b49\u52a8\u6001\u5206\u914d\u65b9\u5f0f\u751f\u6210\uff0c\u5728\u4e0d\u9700\u8981\u65f6\u8981\u91ca\u653e\u76f8\u5e94\u7684\u7a7a\u95f4\u3002<\/p>\n

\u4f18\u70b9 \uff1a\u6bd4\u8d77\u5728\u7ed3\u6784\u4f53\u4e2d\u58f0\u660e\u4e00\u4e2a\u6307\u9488\u53d8\u91cf\u3001\u518d\u8fdb\u884c\u52a8\u6001\u5206 \u914d\u7684\u529e\u6cd5\uff0c\u8fd9\u79cd\u65b9\u6cd5\u6548\u7387\u8981\u9ad8\u3002\u56e0\u4e3a\u5728\u8bbf\u95ee\u6570\u7ec4\u5185\u5bb9\u65f6\uff0c\u4e0d\u9700\u8981\u95f4\u63a5\u8bbf\u95ee\uff0c\u907f\u514d\u4e86\u4e24\u6b21\u8bbf\u5b58\u3002<\/p>\n

\u7f3a\u70b9 \uff1a\u5728\u7ed3\u6784\u4f53\u4e2d\uff0c\u6570\u7ec4\u4e3a0\u7684\u6570\u7ec4\u5fc5\u987b\u5728\u6700\u540e\u58f0\u660e\uff0c\u4f7f \u7528\u4e0a\u6709\u4e00\u5b9a\u9650\u5236\u3002<\/p>\n

\u5bf9\u4e8e\u7f16\u8bd1\u5668\u800c\u8a00, \u6570\u7ec4\u540d\u4ec5\u4ec5\u662f\u4e00\u4e2a\u7b26\u53f7, \u5b83\u4e0d\u4f1a\u5360\u7528\u4efb\u4f55\u7a7a\u95f4, \u5b83\u5728\u7ed3\u6784\u4f53\u4e2d, \u53ea\u662f\u4ee3\u8868\u4e86\u4e00\u4e2a\u504f\u79fb\u91cf, \u4ee3\u8868\u4e00\u4e2a\u4e0d\u53ef\u4fee\u6539\u7684\u5730\u5740\u5e38\u91cf!<\/p>\n

2 0\u957f\u5ea6\u6570\u7ec4\u7684\u7528\u9014
\n\u6211\u4eec\u8bbe\u60f3\u8fd9\u6837\u4e00\u4e2a\u573a\u666f, \u6211\u4eec\u5728\u7f51\u7edc\u901a\u4fe1\u8fc7\u7a0b\u4e2d\u4f7f\u7528\u7684\u6570\u636e\u7f13\u51b2\u533a, \u7f13\u51b2\u533a\u5305\u62ec\u4e00\u4e2alen\u5b57\u6bb5\u548cdata\u5b57\u6bb5, \u5206\u522b\u6807\u8bc6\u6570\u636e\u7684\u957f\u5ea6\u548c\u4f20\u8f93\u7684\u6570\u636e, \u6211\u4eec\u5e38\u89c1\u7684\u6709\u51e0\u79cd\u8bbe\u8ba1\u601d\u8def<\/p>\n

\u5b9a\u957f\u6570\u636e\u7f13\u51b2\u533a, \u8bbe\u7f6e\u4e00\u4e2a\u8db3\u591f\u5927\u5c0f MAX_LENGTH \u7684\u6570\u636e\u7f13\u51b2\u533a<\/p>\n

\u8bbe\u7f6e\u4e00\u4e2a\u6307\u5411\u5b9e\u9645\u6570\u636e\u7684\u6307\u9488, \u6bcf\u6b21\u4f7f\u7528\u65f6, \u6309\u7167\u6570\u636e\u7684\u957f\u5ea6\u52a8\u6001\u7684\u5f00\u8f9f\u6570\u636e\u7f13\u51b2\u533a\u7684\u7a7a\u95f4.<\/p>\n

\u6211\u4eec\u4ece\u5b9e\u9645\u573a\u666f\u4e2d\u5e94\u7528\u7684\u8bbe\u8ba1\u6765\u8003\u8651\u4ed6\u4eec\u7684\u4f18\u52a3. \u4e3b\u8981\u8003\u8651\u7684\u6709, \u7f13\u51b2\u533a\u7a7a\u95f4\u7684\u5f00\u8f9f, \u91ca\u653e\u548c\u8bbf\u95ee.<\/p>\n

2.1 \u5b9a\u957f\u5305(\u5f00\u8f9f\u7a7a\u95f4, \u91ca\u653e, \u8bbf\u95ee)
\n\u6bd4\u5982\u6211\u8981\u53d1\u9001 1024 \u5b57\u8282\u7684\u6570\u636e, \u5982\u679c\u7528\u5b9a\u957f\u5305, \u5047\u8bbe\u5b9a\u957f\u5305\u7684\u957f\u5ea6 MAX_LENGTH \u4e3a 2048, \u5c31\u4f1a\u6d6a\u8d39 1024 \u4e2a\u5b57\u8282\u7684\u7a7a\u95f4, \u4e5f\u4f1a\u9020\u6210\u4e0d\u5fc5\u8981\u7684\u6d41\u91cf\u6d6a\u8d39.<\/p>\n

\u6570\u636e\u7ed3\u6784\u5b9a\u4e49
\n\/\/ \u5b9a\u957f\u7f13\u51b2\u533a
\nstruct max_buffer
\n{
\nint len;
\nchar data[MAX_LENGTH];
\n};
\n1
\n2
\n3
\n4
\n5
\n6
\n\u6570\u636e\u7ed3\u6784\u5927\u5c0f
\n\u8003\u8651\u5bf9\u9f50, \u90a3\u4e48\u6570\u636e\u7ed3\u6784\u7684\u5927\u5c0f >= sizeof(int) + sizeof(char) * MAX_LENGTH<\/p>\n

\u7531\u4e8e\u8003\u8651\u5230\u6570\u636e\u7684\u6ea2\u51fa, \u53d8\u957f\u6570\u636e\u5305\u4e2d\u7684 data \u6570\u7ec4\u957f\u5ea6\u4e00\u822c\u4f1a\u8bbe\u7f6e\u5f97\u8db3\u591f\u957f\u8db3\u4ee5\u5bb9\u7eb3\u6700\u5927\u7684\u6570\u636e, \u56e0\u6b64 max_buffer \u4e2d\u7684 data \u6570\u7ec4\u5f88\u591a\u60c5\u51b5\u4e0b\u90fd\u6ca1\u6709\u586b\u6ee1\u6570\u636e, \u56e0\u6b64\u9020\u6210\u4e86\u6d6a\u8d39<\/p>\n

\u6570\u636e\u5305\u7684\u6784\u9020
\n\u5047\u5982\u6211\u4eec\u8981\u53d1\u9001 CURR_LENGTH = 1024 \u4e2a\u5b57\u8282, \u6211\u4eec\u5982\u4f55\u6784\u9020\u8fd9\u4e2a\u6570\u636e\u5305\u5462:<\/p>\n

\u4e00\u822c\u6765\u8bf4, \u6211\u4eec\u4f1a\u8fd4\u56de\u4e00\u4e2a\u6307\u5411\u7f13\u51b2\u533a\u6570\u636e\u7ed3\u6784 max_buffer \u7684\u6307\u9488.<\/p>\n

\/\/\/ \u5f00\u8f9f
\nif ((mbuffer = (struct max_buffer *)malloc(sizeof(struct max_buffer))) != NULL)
\n{
\nmbuffer->len = CURR_LENGTH;
\nmemcpy(mbuffer->data, “Hello World”, CURR_LENGTH);<\/p>\n

printf(“%d, %s\\n”, mbuffer->len, mbuffer->data);
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n\u8bbf\u95ee
\n\u8fd9\u6bb5\u5185\u5b58\u8981\u5206\u4e24\u90e8\u5206\u4f7f\u7528<\/p>\n

\u524d\u90e8\u5206 4 \u4e2a\u5b57\u8282 p->len, \u4f5c\u4e3a\u5305\u5934(\u5c31\u662f\u591a\u51fa\u6765\u7684\u90a3\u90e8\u5206)\uff0c\u8fd9\u4e2a\u5305\u5934\u662f\u7528\u6765\u63cf\u8ff0\u7d27\u63a5\u7740\u5305\u5934\u540e\u9762\u7684\u6570\u636e\u90e8\u5206\u7684\u957f\u5ea6\uff0c\u8fd9\u91cc\u662f 1024, \u6240\u4ee5\u524d\u56db\u4e2a\u5b57\u8282\u8d4b\u503c\u4e3a 1024 (\u65e2\u7136\u6211\u4eec\u8981\u6784\u9020\u4e0d\u5b9a\u957f\u6570\u636e\u5305\uff0c\u90a3\u4e48\u8fd9\u4e2a\u5305\u5230\u5e95\u6709\u591a\u957f\u5462\uff0c\u56e0\u6b64\uff0c\u6211\u4eec\u5c31\u5fc5\u987b\u901a\u8fc7\u4e00\u4e2a\u53d8\u91cf\u6765\u8868\u660e\u8fd9\u4e2a\u6570\u636e\u5305\u7684\u957f\u5ea6\uff0c\u8fd9\u5c31\u662flen\u7684\u4f5c\u7528)\uff0c<\/p>\n

\u800c\u7d27\u63a5\u5176\u540e\u7684\u5185\u5b58\u662f\u771f\u6b63\u7684\u6570\u636e\u90e8\u5206, \u901a\u8fc7 p->data, \u6700\u540e, \u8fdb\u884c\u4e00\u4e2a memcpy() \u5185\u5b58\u62f7\u8d1d, \u628a\u8981\u53d1\u9001\u7684\u6570\u636e\u586b\u5165\u5230\u8fd9\u6bb5\u5185\u5b58\u5f53\u4e2d<\/p>\n

\u91ca\u653e
\n\u90a3\u4e48\u5f53\u4f7f\u7528\u5b8c\u6bd5\u91ca\u653e\u6570\u636e\u7684\u7a7a\u95f4\u7684\u65f6\u5019, \u76f4\u63a5\u91ca\u653e\u5c31\u53ef\u4ee5\u4e86<\/p>\n

\/\/\/ \u9500\u6bc1
\nfree(mbuffer);
\nmbuffer = NULL;
\n1
\n2
\n3
\n\u5c0f\u7ed3<\/p>\n

\u4f7f\u7528\u5b9a\u957f\u6570\u7ec4, \u4f5c\u4e3a\u6570\u636e\u7f13\u51b2\u533a, \u4e3a\u4e86\u907f\u514d\u9020\u6210\u7f13\u51b2\u533a\u6ea2\u51fa, \u6570\u7ec4\u7684\u5927\u5c0f\u4e00\u822c\u8bbe\u4e3a\u8db3\u591f\u7684\u7a7a\u95f4 MAX_LENGTH, \u800c\u5b9e\u9645\u4f7f\u7528\u8fc7\u7a0b\u4e2d, \u8fbe\u5230 MAX_LENGTH \u957f\u5ea6\u7684\u6570\u636e\u5f88\u5c11, \u90a3\u4e48\u591a\u6570\u60c5\u51b5\u4e0b, \u7f13\u51b2\u533a\u7684\u5927\u90e8\u5206\u7a7a\u95f4\u90fd\u662f\u6d6a\u8d39\u6389\u7684.<\/p>\n

\u4f46\u662f\u4f7f\u7528\u8fc7\u7a0b\u5f88\u7b80\u5355, \u6570\u636e\u7a7a\u95f4\u7684\u5f00\u8f9f\u548c\u91ca\u653e\u7b80\u5355, \u65e0\u9700\u7a0b\u5e8f\u5458\u8003\u8651\u989d\u5916\u7684\u64cd\u4f5c<\/p>\n

2.2 \u6307\u9488\u6570\u636e\u5305(\u5f00\u8f9f\u7a7a\u95f4, \u91ca\u653e, \u8bbf\u95ee)
\n\u5982\u679c\u4f60\u5c06\u4e0a\u9762\u7684\u957f\u5ea6\u4e3a MAX_LENGTH \u7684\u5b9a\u957f\u6570\u7ec4\u6362\u4e3a\u6307\u9488, \u6bcf\u6b21\u4f7f\u7528\u65f6\u52a8\u6001\u7684\u5f00\u8f9f CURR_LENGTH \u5927\u5c0f\u7684\u7a7a\u95f4, \u90a3\u4e48\u5c31\u907f\u514d\u9020\u6210 MAX_LENGTH – CURR_LENGTH \u7a7a\u95f4\u7684\u6d6a\u8d39, \u53ea\u6d6a\u8d39\u4e86\u4e00\u4e2a\u6307\u9488\u57df\u7684\u7a7a\u95f4.<\/p>\n

\u6570\u636e\u5305\u5b9a\u4e49
\nstruct point_buffer
\n{
\nint len;
\nchar *data;
\n};
\n1
\n2
\n3
\n4
\n5
\n\u6570\u636e\u7ed3\u6784\u5927\u5c0f
\n\u8003\u8651\u5bf9\u9f50, \u90a3\u4e48\u6570\u636e\u7ed3\u6784\u7684\u5927\u5c0f >= sizeof(int) + sizeof(char *)<\/p>\n

\u7a7a\u95f4\u5206\u914d
\n\u4f46\u662f\u4e5f\u9020\u6210\u4e86\u4f7f\u7528\u5728\u5206\u914d\u5185\u5b58\u65f6\uff0c\u9700\u91c7\u7528\u4e24\u6b65<\/p>\n

\/\/ =====================
\n\/\/ \u6307\u9488\u6570\u7ec4 \u5360\u7528-\u5f00\u8f9f-\u9500\u6bc1
\n\/\/ =====================
\n\/\/\/ \u5360\u7528
\nprintf(“the length of struct test3:%d\\n”,sizeof(struct point_buffer));
\n\/\/\/ \u5f00\u8f9f
\nif ((pbuffer = (struct point_buffer *)malloc(sizeof(struct point_buffer))) != NULL)
\n{
\npbuffer->len = CURR_LENGTH;
\nif ((pbuffer->data = (char *)malloc(sizeof(char) * CURR_LENGTH)) != NULL)
\n{
\nmemcpy(pbuffer->data, “Hello World”, CURR_LENGTH);<\/p>\n

printf(“%d, %s\\n”, pbuffer->len, pbuffer->data);
\n}
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\n16
\n17
\n\u9996\u5148, \u9700\u4e3a\u7ed3\u6784\u4f53\u5206\u914d\u4e00\u5757\u5185\u5b58\u7a7a\u95f4;<\/p>\n

\u5176\u6b21\u518d\u4e3a\u7ed3\u6784\u4f53\u4e2d\u7684\u6210\u5458\u53d8\u91cf\u5206\u914d\u5185\u5b58\u7a7a\u95f4.<\/p>\n

\u8fd9\u6837\u4e24\u6b21\u5206\u914d\u7684\u5185\u5b58\u662f\u4e0d\u8fde\u7eed\u7684, \u9700\u8981\u5206\u522b\u5bf9\u5176\u8fdb\u884c\u7ba1\u7406. \u5f53\u4f7f\u7528\u957f\u5ea6\u4e3a\u7684\u6570\u7ec4\u65f6, \u5219\u662f\u91c7\u7528\u4e00\u6b21\u5206\u914d\u7684\u539f\u5219, \u4e00\u6b21\u6027\u5c06\u6240\u9700\u7684\u5185\u5b58\u5168\u90e8\u5206\u914d\u7ed9\u5b83.<\/p>\n

\u91ca\u653e
\n\u76f8\u53cd, \u91ca\u653e\u65f6\u4e5f\u662f\u4e00\u6837\u7684.<\/p>\n

\/\/\/ \u9500\u6bc1
\nfree(pbuffer->data);
\nfree(pbuffer);
\npbuffer = NULL;
\n1
\n2
\n3
\n4
\n\u5c0f\u7ed3<\/p>\n

\u4f7f\u7528\u6307\u9488\u7ed3\u679c\u4f5c\u4e3a\u7f13\u51b2\u533a, \u53ea\u591a\u4f7f\u7528\u4e86\u4e00\u4e2a\u6307\u9488\u5927\u5c0f\u7684\u7a7a\u95f4, \u65e0\u9700\u4f7f\u7528 MAX_LENGTH \u957f\u5ea6\u7684\u6570\u7ec4, \u4e0d\u4f1a\u9020\u6210\u7a7a\u95f4\u7684\u5927\u91cf\u6d6a\u8d39.<\/p>\n

\u4f46\u90a3\u662f\u5f00\u8f9f\u7a7a\u95f4\u65f6, \u9700\u8981\u989d\u5916\u5f00\u8f9f\u6570\u636e\u57df\u7684\u7a7a\u95f4, \u65bd\u653e\u65f6\u5019\u4e5f\u9700\u8981\u663e\u793a\u91ca\u653e\u6570\u636e\u57df\u7684\u7a7a\u95f4, \u4f46\u662f\u5b9e\u9645\u4f7f\u7528\u8fc7\u7a0b\u4e2d, \u5f80\u5f80\u5728\u51fd\u6570\u4e2d\u5f00\u8f9f\u7a7a\u95f4, \u7136\u540e\u8fd4\u56de\u7ed9\u4f7f\u7528\u8005\u6307\u5411 struct point_buffer \u7684\u6307\u9488, \u8fd9\u65f6\u5019\u6211\u4eec\u5e76\u4e0d\u80fd\u5047\u5b9a\u4f7f\u7528\u8005\u4e86\u89e3\u6211\u4eec\u5f00\u8f9f\u7684\u7ec6\u8282, \u5e76\u6309\u7167\u7ea6\u5b9a\u7684\u64cd\u4f5c\u91ca\u653e\u7a7a\u95f4, \u56e0\u6b64\u4f7f\u7528\u8d77\u6765\u591a\u6709\u4e0d\u4fbf, \u751a\u81f3\u9020\u6210\u5185\u5b58\u6cc4\u6f0f<\/p>\n

2.3 \u53d8\u957f\u6570\u636e\u7f13\u51b2\u533a(\u5f00\u8f9f\u7a7a\u95f4, \u91ca\u653e, \u8bbf\u95ee)
\n\u5b9a\u957f\u6570\u7ec4\u4f7f\u7528\u65b9\u4fbf, \u4f46\u662f\u5374\u6d6a\u8d39\u7a7a\u95f4, \u6307\u9488\u5f62\u5f0f\u53ea\u591a\u4f7f\u7528\u4e86\u4e00\u4e2a\u6307\u9488\u7684\u7a7a\u95f4, \u4e0d\u4f1a\u9020\u6210\u5927\u91cf\u7a7a\u95f4\u5206\u6d6a\u8d39, \u4f46\u662f\u4f7f\u7528\u8d77\u6765\u9700\u8981\u591a\u6b21\u5206\u914d, \u591a\u6b21\u91ca\u653e, \u90a3\u4e48\u6709\u6ca1\u6709\u4e00\u79cd\u5b9e\u73b0\u65b9\u5f0f\u80fd\u591f\u65e2\u4e0d\u6d6a\u8d39\u7a7a\u95f4, \u53c8\u4f7f\u7528\u65b9\u4fbf\u7684\u5462?<\/p>\n

GNU C \u76840\u957f\u5ea6\u6570\u7ec4, \u4e5f\u53eb\u53d8\u957f\u6570\u7ec4, \u67d4\u6027\u6570\u7ec4\u5c31\u662f\u8fd9\u6837\u4e00\u4e2a\u6269\u5c55. \u5bf9\u4e8e0\u957f\u6570\u7ec4\u7684\u8fd9\u4e2a\u7279\u70b9\uff0c\u5f88\u5bb9\u6613\u6784\u9020\u51fa\u53d8\u6210\u7ed3\u6784\u4f53\uff0c\u5982\u7f13\u51b2\u533a\uff0c\u6570\u636e\u5305\u7b49\u7b49\uff1a<\/p>\n

\u6570\u636e\u7ed3\u6784\u5b9a\u4e49
\n\/\/ 0\u957f\u5ea6\u6570\u7ec4
\nstruct zero_buffer
\n{
\nint len;
\nchar data[0];
\n};
\n1
\n2
\n3
\n4
\n5
\n6
\n\u6570\u636e\u7ed3\u6784\u5927\u5c0f
\n\u8fd9\u6837\u7684\u53d8\u957f\u6570\u7ec4\u5e38\u7528\u4e8e\u7f51\u7edc\u901a\u4fe1\u4e2d\u6784\u9020\u4e0d\u5b9a\u957f\u6570\u636e\u5305, \u4e0d\u4f1a\u6d6a\u8d39\u7a7a\u95f4\u6d6a\u8d39\u7f51\u7edc\u6d41\u91cf, \u56e0\u4e3achar data[0]; \u53ea\u662f\u4e2a\u6570\u7ec4\u540d, \u662f\u4e0d\u5360\u7528\u5b58\u50a8\u7a7a\u95f4\u7684,<\/p>\n

\u5373 sizeof(struct zero_buffer) = sizeof(int)<\/p>\n

\u5f00\u8f9f\u7a7a\u95f4
\n\u90a3\u4e48\u6211\u4eec\u4f7f\u7528\u7684\u65f6\u5019, \u53ea\u9700\u8981\u5f00\u8f9f\u4e00\u6b21\u7a7a\u95f4\u5373\u53ef<\/p>\n

\/\/\/ \u5f00\u8f9f
\nif ((zbuffer = (struct zero_buffer *)malloc(sizeof(struct zero_buffer) + sizeof(char) * CURR_LENGTH)) != NULL)
\n{
\nzbuffer->len = CURR_LENGTH;
\nmemcpy(zbuffer->data, “Hello World”, CURR_LENGTH);<\/p>\n

printf(“%d, %s\\n”, zbuffer->len, zbuffer->data);
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n\u91ca\u653e\u7a7a\u95f4
\n\u91ca\u653e\u7a7a\u95f4\u4e5f\u662f\u4e00\u6837\u7684, \u4e00\u6b21\u91ca\u653e\u5373\u53ef<\/p>\n

\/\/\/ \u9500\u6bc1
\nfree(zbuffer);
\nzbuffer = NULL;
\n1
\n2
\n3
\n2.4 \u603b\u7ed3
\n\/\/ zero_length_array.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

#define MAX_LENGTH 1024
\n#define CURR_LENGTH 512<\/p>\n

\/\/ 0\u957f\u5ea6\u6570\u7ec4
\nstruct zero_buffer
\n{
\nint len;
\nchar data[0];
\n}__attribute((packed));<\/p>\n

\/\/ \u5b9a\u957f\u6570\u7ec4
\nstruct max_buffer
\n{
\nint len;
\nchar data[MAX_LENGTH];
\n}__attribute((packed));<\/p>\n

\/\/ \u6307\u9488\u6570\u7ec4
\nstruct point_buffer
\n{
\nint len;
\nchar *data;
\n}__attribute((packed));<\/p>\n

int main(void)
\n{
\nstruct zero_buffer *zbuffer = NULL;
\nstruct max_buffer *mbuffer = NULL;
\nstruct point_buffer *pbuffer = NULL;<\/p>\n

\/\/ =====================
\n\/\/ 0\u957f\u5ea6\u6570\u7ec4 \u5360\u7528-\u5f00\u8f9f-\u9500\u6bc1
\n\/\/ =====================
\n\/\/\/ \u5360\u7528
\nprintf(“the length of struct test1:%d\\n”,sizeof(struct zero_buffer));
\n\/\/\/ \u5f00\u8f9f
\nif ((zbuffer = (struct zero_buffer *)malloc(sizeof(struct zero_buffer) + sizeof(char) * CURR_LENGTH)) != NULL)
\n{
\nzbuffer->len = CURR_LENGTH;
\nmemcpy(zbuffer->data, “Hello World”, CURR_LENGTH);<\/p>\n

printf(“%d, %s\\n”, zbuffer->len, zbuffer->data);
\n}
\n\/\/\/ \u9500\u6bc1
\nfree(zbuffer);
\nzbuffer = NULL;<\/p>\n

\/\/ =====================
\n\/\/ \u5b9a\u957f\u6570\u7ec4 \u5360\u7528-\u5f00\u8f9f-\u9500\u6bc1
\n\/\/ =====================
\n\/\/\/ \u5360\u7528
\nprintf(“the length of struct test2:%d\\n”,sizeof(struct max_buffer));
\n\/\/\/ \u5f00\u8f9f
\nif ((mbuffer = (struct max_buffer *)malloc(sizeof(struct max_buffer))) != NULL)
\n{
\nmbuffer->len = CURR_LENGTH;
\nmemcpy(mbuffer->data, “Hello World”, CURR_LENGTH);<\/p>\n

printf(“%d, %s\\n”, mbuffer->len, mbuffer->data);
\n}
\n\/\/\/ \u9500\u6bc1
\nfree(mbuffer);
\nmbuffer = NULL;<\/p>\n

\/\/ =====================
\n\/\/ \u6307\u9488\u6570\u7ec4 \u5360\u7528-\u5f00\u8f9f-\u9500\u6bc1
\n\/\/ =====================
\n\/\/\/ \u5360\u7528
\nprintf(“the length of struct test3:%d\\n”,sizeof(struct point_buffer));
\n\/\/\/ \u5f00\u8f9f
\nif ((pbuffer = (struct point_buffer *)malloc(sizeof(struct point_buffer))) != NULL)
\n{
\npbuffer->len = CURR_LENGTH;
\nif ((pbuffer->data = (char *)malloc(sizeof(char) * CURR_LENGTH)) != NULL)
\n{
\nmemcpy(pbuffer->data, “Hello World”, CURR_LENGTH);<\/p>\n

printf(“%d, %s\\n”, pbuffer->len, pbuffer->data);
\n}
\n}
\n\/\/\/ \u9500\u6bc1
\nfree(pbuffer->data);
\nfree(pbuffer);
\npbuffer = NULL;<\/p>\n

return EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\n16
\n17
\n18
\n19
\n20
\n21
\n22
\n23
\n24
\n25
\n26
\n27
\n28
\n29
\n30
\n31
\n32
\n33
\n34
\n35
\n36
\n37
\n38
\n39
\n40
\n41
\n42
\n43
\n44
\n45
\n46
\n47
\n48
\n49
\n50
\n51
\n52
\n53
\n54
\n55
\n56
\n57
\n58
\n59
\n60
\n61
\n62
\n63
\n64
\n65
\n66
\n67
\n68
\n69
\n70
\n71
\n72
\n73
\n74
\n75
\n76
\n77
\n78
\n79
\n80
\n81
\n82
\n83
\n84
\n85
\n86
\n87
\n88
\n89
\n90
\n91
\n92
\n93
\n94
\n95
\n96
\n97
\n98
\n99
\n100<\/p>\n

\u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4\u5e76\u4e0d\u5360\u6709\u5185\u5b58\u7a7a\u95f4, \u800c\u6307\u9488\u65b9\u5f0f\u9700\u8981\u5360\u7528\u5185\u5b58\u7a7a\u95f4.<\/p>\n

\u5bf9\u4e8e\u957f\u5ea6\u4e3a0\u6570\u7ec4, \u5728\u7533\u8bf7\u5185\u5b58\u7a7a\u95f4\u65f6, \u91c7\u7528\u4e00\u6b21\u6027\u5206\u914d\u7684\u539f\u5219\u8fdb\u884c; \u5bf9\u4e8e\u5305\u542b\u6307\u9488\u7684\u7ed3\u6784\u4f53, \u624d\u7533\u8bf7\u7a7a\u95f4\u65f6\u9700\u5206\u522b\u8fdb\u884c, \u91ca\u653e\u65f6\u4e5f\u9700\u5206\u522b\u91ca\u653e.<\/p>\n

\u5bf9\u4e8e\u957f\u5ea6\u4e3a\u7684\u6570\u7ec4\u7684\u8bbf\u95ee\u53ef\u91c7\u7528\u6570\u7ec4\u65b9\u5f0f\u8fdb\u884c<\/p>\n

3 GNU Document\u4e2d \u53d8\u957f\u6570\u7ec4\u7684\u652f\u6301
\n\u53c2\u89c1<\/p>\n

6.17 Arrays of Length Zero<\/p>\n

C Struct Hack \u2013 Structure with variable length array<\/p>\n

\u5728 C90 \u4e4b\u524d, \u5e76\u4e0d\u652f\u63010\u957f\u5ea6\u7684\u6570\u7ec4, 0\u957f\u5ea6\u6570\u7ec4\u662f GNU C \u7684\u4e00\u4e2a\u6269\u5c55, \u56e0\u6b64\u65e9\u671f\u7684\u7f16\u8bd1\u5668\u4e2d\u662f\u65e0\u6cd5\u901a\u8fc7\u7f16\u8bd1\u7684<\/p>\n

\u5bf9\u4e8e GNU C \u589e\u52a0\u7684\u6269\u5c55, GCC \u63d0\u4f9b\u4e86\u7f16\u8bd1\u9009\u9879\u6765\u660e\u786e\u7684\u6807\u8bc6\u51fa\u4ed6\u4eec<\/p>\n

1\u3001-pedantic \u9009\u9879\uff0c\u90a3\u4e48\u4f7f\u7528\u4e86\u6269\u5c55\u8bed\u6cd5\u7684\u5730\u65b9\u5c06\u4ea7\u751f\u76f8\u5e94\u7684\u8b66\u544a\u4fe1\u606f<\/p>\n

2\u3001-Wall \u4f7f\u7528\u5b83\u80fd\u591f\u4f7fGCC\u4ea7\u751f\u5c3d\u53ef\u80fd\u591a\u7684\u8b66\u544a\u4fe1\u606f<\/p>\n

3\u3001-Werror, \u5b83\u8981\u6c42GCC\u5c06\u6240\u6709\u7684\u8b66\u544a\u5f53\u6210\u9519\u8bef\u8fdb\u884c\u5904\u7406<\/p>\n

\/\/ 1.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

int main(void)
\n{
\nchar a[0];
\nprintf(“%ld”, sizeof(a));
\nreturn EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n\u6211\u4eec\u6765\u7f16\u8bd1<\/p>\n

gcc 1.c -Wall # \u663e\u793a\u6240\u6709\u8b66\u544a
\n#none warning and error<\/p>\n

gcc 1.c -Wall -pedantic # \u5bf9GNU C\u7684\u6269\u5c55\u663e\u793a\u8b66\u544a
\n1.c: In function \u2018main\u2019:
\n1.c:7: warning: ISO C forbids zero-size array \u2018a\u2019<\/p>\n

gcc 1.c -Werror -Wall -pedantic # \u663e\u793a\u6240\u6709\u8b66\u544a\u540c\u65f6GNU C\u7684\u6269\u5c55\u663e\u793a\u8b66\u544a, \u5c06\u8b66\u544a\u7528error\u663e\u793a
\ncc1: warnings being treated as errors
\n1.c: In function \u2018main\u2019:
\n1.c:7: error: ISO C forbids zero-size array \u2018a\u2019
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12<\/p>\n

0\u957f\u5ea6\u6570\u7ec4\u5176\u5b9e\u5c31\u662f\u7075\u6d3b\u7684\u8fd0\u7528\u7684\u6570\u7ec4\u6307\u5411\u7684\u662f\u5176\u540e\u9762\u7684\u8fde\u7eed\u7684\u5185\u5b58\u7a7a\u95f4<\/p>\n

struct buffer
\n{
\nint len;
\nchar data[0];
\n};
\n1
\n2
\n3
\n4
\n5
\n\u5728\u65e9\u671f\u6ca1\u5f15\u51650\u957f\u5ea6\u6570\u7ec4\u7684\u65f6\u5019, \u5927\u5bb6\u662f\u901a\u8fc7\u5b9a\u957f\u6570\u7ec4\u548c\u6307\u9488\u7684\u65b9\u5f0f\u6765\u89e3\u51b3\u7684, \u4f46\u662f<\/p>\n

\u5b9a\u957f\u6570\u7ec4\u5b9a\u4e49\u4e86\u4e00\u4e2a\u8db3\u591f\u5927\u7684\u7f13\u51b2\u533a, \u8fd9\u6837\u4f7f\u7528\u65b9\u4fbf, \u4f46\u662f\u6bcf\u6b21\u90fd\u9020\u6210\u7a7a\u95f4\u7684\u6d6a\u8d39
\n\u6307\u9488\u7684\u65b9\u5f0f, \u8981\u6c42\u7a0b\u5e8f\u5458\u5728\u91ca\u653e\u7a7a\u95f4\u662f\u5fc5\u987b\u8fdb\u884c\u591a\u6b21\u7684free\u64cd\u4f5c, \u800c\u6211\u4eec\u5728\u4f7f\u7528\u7684\u8fc7\u7a0b\u4e2d\u5f80\u5f80\u5728\u51fd\u6570\u4e2d\u8fd4\u56de\u4e86\u6307\u5411\u7f13\u51b2\u533a\u7684\u6307\u9488, \u6211\u4eec\u5e76\u4e0d\u80fd\u4fdd\u8bc1\u6bcf\u4e2a\u4eba\u90fd\u7406\u89e3\u5e76\u9075\u4ece\u6211\u4eec\u7684\u91ca\u653e\u65b9\u5f0f
\n\u6240\u4ee5 GNU \u5c31\u5bf9\u5176\u8fdb\u884c\u4e860\u957f\u5ea6\u6570\u7ec4\u7684\u6269\u5c55. \u5f53\u4f7f\u7528data[0]\u7684\u65f6\u5019, \u4e5f\u5c31\u662f0\u957f\u5ea6\u6570\u7ec4\u7684\u65f6\u5019\uff0c0\u957f\u5ea6\u6570\u7ec4\u4f5c\u4e3a\u6570\u7ec4\u540d, \u5e76\u4e0d\u5360\u7528\u5b58\u50a8\u7a7a\u95f4.<\/p>\n

\u5728C99\u4e4b\u540e\uff0c\u4e5f\u52a0\u4e86\u7c7b\u4f3c\u7684\u6269\u5c55\uff0c\u53ea\u4e0d\u8fc7\u7528\u7684\u662f char payload[]\u8fd9\u79cd\u5f62\u5f0f\uff08\u6240\u4ee5\u5982\u679c\u4f60\u5728\u7f16\u8bd1\u7684\u65f6\u5019\u786e\u5b9e\u9700\u8981\u7528\u5230-pedantic\u53c2\u6570\uff0c\u90a3\u4e48\u4f60\u53ef\u4ee5\u5c06char payload[0]\u7c7b\u578b\u6539\u6210char payload[], \u8fd9\u6837\u5c31\u53ef\u4ee5\u7f16\u8bd1\u901a\u8fc7\u4e86\uff0c\u5f53\u7136\u4f60\u7684\u7f16\u8bd1\u5668\u5fc5\u987b\u652f\u6301C99\u6807\u51c6\u7684\uff0c\u5982\u679c\u592a\u53e4\u8001\u7684\u7f16\u8bd1\u5668\uff0c\u90a3\u53ef\u80fd\u4e0d\u652f\u6301\u4e86)<\/p>\n

\/\/ 2.c payload
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

struct payload
\n{
\nint len;
\nchar data[];
\n};<\/p>\n

int main(void)
\n{
\nstruct payload pay;
\nprintf(“%ld”, sizeof(pay));
\nreturn EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\n16
\n\u4f7f\u7528 -pedantic \u7f16\u8bd1\u540e, \u4e0d\u51fa\u73b0\u8b66\u544a, \u8bf4\u660e\u8fd9\u79cd\u8bed\u6cd5\u662f C \u6807\u51c6\u7684<\/p>\n

gcc 2.c -pedantic -std=c99
\n1<\/p>\n

\u6240\u4ee5\u7ed3\u6784\u4f53\u7684\u672b\u5c3e, \u5c31\u662f\u6307\u5411\u4e86\u5176\u540e\u9762\u7684\u5185\u5b58\u6570\u636e\u3002\u56e0\u6b64\u6211\u4eec\u53ef\u4ee5\u5f88\u597d\u7684\u5c06\u8be5\u7c7b\u578b\u7684\u7ed3\u6784\u4f53\u4f5c\u4e3a\u6570\u636e\u62a5\u6587\u7684\u5934\u683c\u5f0f\uff0c\u5e76\u4e14\u6700\u540e\u4e00\u4e2a\u6210\u5458\u53d8\u91cf\uff0c\u4e5f\u5c31\u521a\u597d\u662f\u6570\u636e\u5185\u5bb9\u4e86.<\/p>\n

GNU\u624b\u518c\u8fd8\u63d0\u4f9b\u4e86\u53e6\u5916\u4e24\u4e2a\u7ed3\u6784\u4f53\u6765\u8bf4\u660e\uff0c\u66f4\u5bb9\u6613\u770b\u61c2\u610f\u601d\uff1a<\/p>\n

struct f1 {
\nint x;
\nint y[];
\n} f1 = { 1, { 2, 3, 4 } };<\/p>\n

struct f2 {
\nstruct f1 f1;
\nint data[3];
\n} f2 = { { 1 }, { 5, 6, 7 } };
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n\u6211\u628af2\u91cc\u9762\u76842,3,4\u6539\u6210\u4e865,6,7\u4ee5\u793a\u533a\u5206\u3002\u5982\u679c\u4f60\u628a\u6570\u636e\u6253\u51fa\u6765\u3002\u5373\u5982\u4e0b\u7684\u4fe1\u606f\uff1a<\/p>\n

f1.x = 1
\nf1.y[0] = 2
\nf1.y[1] = 3
\nf1.y[2] = 4
\n1
\n2
\n3
\n4
\n\u4e5f\u5c31\u662ff1.y\u6307\u5411\u7684\u662f{2,3,4}\u8fd9\u5757\u5185\u5b58\u4e2d\u7684\u6570\u636e\u3002\u6240\u4ee5\u6211\u4eec\u5c31\u53ef\u4ee5\u8f7b\u6613\u7684\u5f97\u5230\uff0cf2.f1.y\u6307\u5411\u7684\u6570\u636e\u4e5f\u5c31\u662f\u6b63\u597df2.data\u7684\u5185\u5bb9\u4e86\u3002\u6253\u5370\u51fa\u6765\u7684\u6570\u636e\uff1a<\/p>\n

f2.f1.x = 1
\nf2.f1.y[0] = 5
\nf2.f1.y[1] = 6
\nf2.f1.y[2] = 7
\n1
\n2
\n3
\n4
\n\u5982\u679c\u4f60\u4e0d\u662f\u5f88\u786e\u8ba4\u5176\u662f\u5426\u5360\u7528\u7a7a\u95f4. \u4f60\u53ef\u4ee5\u7528sizeof\u6765\u8ba1\u7b97\u4e00\u4e0b\u3002\u5c31\u53ef\u4ee5\u77e5\u9053sizeof(struct f1)=4,\u4e5f\u5c31\u662fint y[]\u5176\u5b9e\u662f\u4e0d\u5360\u7528\u7a7a\u95f4\u7684\u3002\u4f46\u662f\u8fd9\u4e2a0\u957f\u5ea6\u7684\u6570\u7ec4\uff0c\u5fc5\u987b\u653e\u5728\u7ed3\u6784\u4f53\u7684\u672b\u5c3e\u3002\u5982\u679c\u4f60\u6ca1\u6709\u628a\u5b83\u653e\u5728\u672b\u5c3e\u7684\u8bdd\u3002\u7f16\u8bd1\u7684\u65f6\u5019\uff0c\u4f1a\u6709\u5982\u4e0b\u7684\u9519\u8bef\uff1a<\/p>\n

main.c:37:9: error: flexible array member not at end of struct
\nint y[];
\n^
\n1
\n2
\n3
\n\u5230\u8fd9\u8fb9\uff0c\u4f60\u53ef\u80fd\u4f1a\u6709\u7591\u95ee\uff0c\u5982\u679c\u5c06struct f1\u4e2d\u7684int y[]\u66ff\u6362\u6210int *y\uff0c\u53c8\u4f1a\u662f\u5982\u4f55\uff1f\u8fd9\u5c31\u6d89\u53ca\u5230\u6570\u7ec4\u548c\u6307\u9488\u7684\u95ee\u9898\u4e86. \u6709\u65f6\u5019\u5427\uff0c\u8fd9\u4e24\u4e2a\u662f\u4e00\u6837\u7684\uff0c\u6709\u65f6\u5019\u53c8\u6709\u533a\u522b\u3002<\/p>\n

\u9996\u5148\u8981\u8bf4\u660e\u7684\u662f\uff0c\u652f\u63010\u957f\u5ea6\u6570\u7ec4\u7684\u6269\u5c55\uff0c\u91cd\u70b9\u5728\u6570\u7ec4\uff0c\u4e5f\u5c31\u662f\u4e0d\u80fd\u7528int *y\u6307\u9488\u6765\u66ff\u6362\u3002sizeof\u7684\u957f\u5ea6\u5c31\u4e0d\u4e00\u6837\u4e86\u3002\u628astruct f1\u6539\u6210\u8fd9\u6837\uff1a<\/p>\n

struct f3 {
\nint x;
\nint *y;
\n};
\n1
\n2
\n3
\n4
\n\u572832\/64\u4f4d\u4e0b, int\u5747\u662f4\u4e2a\u5b57\u8282, sizeof(struct f1)=4\uff0c\u800csizeof(struct f3)=16<\/p>\n

\u56e0\u4e3a int *y \u662f\u6307\u9488, \u6307\u9488\u572864\u4f4d\u4e0b, \u662f64\u4f4d\u7684\uff0c sizeof(struct f3) = 16, \u5982\u679c\u572832\u4f4d\u73af\u5883\u7684\u8bdd, sizeof(struct f3) \u5219\u662f 8 \u4e86, sizeof(struct f1) \u4e0d\u53d8. \u6240\u4ee5 int *y \u662f\u4e0d\u80fd\u66ff\u4ee3 int y[] \u7684.<\/p>\n

\u4ee3\u7801\u5982\u4e0b<\/p>\n

\/\/ 3.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

struct f1 {
\nint x;
\nint y[];
\n} f1 = { 1, { 2, 3, 4 } };<\/p>\n

struct f2 {
\nstruct f1 f1;
\nint data[3];
\n} f2 = { { 1 }, { 5, 6, 7 } };<\/p>\n

struct f3
\n{
\nint x;
\nint *y;
\n};<\/p>\n

int main(void)
\n{
\nprintf(“sizeof(f1) = %d\\n”, sizeof(struct f1));
\nprintf(“sizeof(f2) = %d\\n”, sizeof(struct f2));
\nprintf(“szieof(f3) = %d\\n\\n”, sizeof(struct f3));<\/p>\n

printf(“f1.x = %d\\n”, f1.x);
\nprintf(“f1.y[0] = %d\\n”, f1.y[0]);
\nprintf(“f1.y[1] = %d\\n”, f1.y[1]);
\nprintf(“f1.y[2] = %d\\n”, f1.y[2]);<\/p>\n

printf(“f2.f1.x = %d\\n”, f1.x);
\nprintf(“f2.f1.y[0] = %d\\n”, f2.f1.y[0]);
\nprintf(“f2.f1.y[1] = %d\\n”, f2.f1.y[1]);
\nprintf(“f2.f1.y[2] = %d\\n”, f2.f1.y[2]);<\/p>\n

return EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\n16
\n17
\n18
\n19
\n20
\n21
\n22
\n23
\n24
\n25
\n26
\n27
\n28
\n29
\n30
\n31
\n32
\n33
\n34
\n35
\n36
\n37
\n38
\n39
\n40
\n41<\/p>\n

4 0\u957f\u5ea6\u6570\u7ec4\u7684\u5176\u4ed6\u7279\u5f81
\n4.1 \u4e3a\u4ec0\u4e480\u957f\u5ea6\u6570\u7ec4\u4e0d\u5360\u7528\u5b58\u50a8\u7a7a\u95f4
\n\u53c2\u89c1<\/p>\n

\u7ed3\u6784\u4f53\u4e2d\u7684\u6307\u9488\u4e0e\u96f6\u957f\u5ea6\u6570\u7ec4<\/p>\n

GNU C\u4e2d\u7684\u96f6\u957f\u5ea6\u6570\u7ec4<\/p>\n

0\u957f\u5ea6\u6570\u7ec4\u4e0e\u6307\u9488\u5b9e\u73b0\u6709\u4ec0\u4e48\u533a\u522b\u5462, \u4e3a\u4ec0\u4e480\u957f\u5ea6\u6570\u7ec4\u4e0d\u5360\u7528\u5b58\u50a8\u7a7a\u95f4\u5462?<\/p>\n

\u5176\u5b9e\u672c\u8d28\u4e0a\u6d89\u53ca\u5230\u7684\u662f\u4e00\u4e2aC\u8bed\u8a00\u91cc\u9762\u7684\u6570\u7ec4\u548c\u6307\u9488\u7684\u533a\u522b\u95ee\u9898. char a[1]\u91cc\u9762\u7684a\u548cchar *b\u7684b\u76f8\u540c\u5417\uff1f<\/p>\n

\u300a Programming Abstractions in C\u300b\uff08Roberts, E. S.\uff0c\u673a\u68b0\u5de5\u4e1a\u51fa\u7248\u793e\uff0c2004.6\uff0982\u9875\u91cc\u9762\u8bf4<\/p>\n

\u201carr is defined to be identical to &arr[0]\u201d.<\/p>\n

\u4e5f\u5c31\u662f\u8bf4\uff0cchar a[1]\u91cc\u9762\u7684a\u5b9e\u9645\u662f\u4e00\u4e2a\u5e38\u91cf\uff0c\u7b49\u4e8e&a[0]\u3002\u800cchar *b\u662f\u6709\u4e00\u4e2a\u5b9e\u5b9e\u5728\u5728\u7684\u6307\u9488\u53d8\u91cfb\u5b58\u5728\u3002 \u6240\u4ee5\uff0ca=b\u662f\u4e0d\u5141\u8bb8\u7684\uff0c\u800cb=a\u662f\u5141\u8bb8\u7684\u3002 \u4e24\u79cd\u53d8\u91cf\u90fd\u652f\u6301\u4e0b\u6807\u5f0f\u7684\u8bbf\u95ee\uff0c\u90a3\u4e48\u5bf9\u4e8ea[0]\u548cb[0]\u672c\u8d28\u4e0a\u662f\u5426\u6709\u533a\u522b\uff1f\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u4e00\u4e2a\u4f8b\u5b50\u6765\u8bf4\u660e\u3002<\/p>\n

\u53c2\u89c1\u5982\u4e0b\u4e24\u4e2a\u7a0b\u5e8f gdb_zero_length_array.c \u548c gdb_zero_length_array.c<\/p>\n

\/\/ gdb_zero_length_array.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

struct str
\n{
\nint len;
\nchar s[0];
\n};<\/p>\n

struct foo
\n{
\nstruct str *a;
\n};<\/p>\n

int main(void)
\n{
\nstruct foo f = { NULL };<\/p>\n

printf(“sizeof(struct str) = %d\\n”, sizeof(struct str));<\/p>\n

printf(“before f.a->s.\\n”);
\nif(f.a->s)
\n{
\nprintf(“before printf f.a->s.\\n”);
\nprintf(f.a->s);
\nprintf(“before printf f.a->s.\\n”);
\n}<\/p>\n

return EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\n16
\n17
\n18
\n19
\n20
\n21
\n22
\n23
\n24
\n25
\n26
\n27
\n28
\n29
\n30
\n31<\/p>\n

\/\/ gdb_pzero_length_array.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

struct str
\n{
\nint len;
\nchar *s;
\n};<\/p>\n

struct foo
\n{
\nstruct str *a;
\n};<\/p>\n

int main(void)
\n{
\nstruct foo f = { NULL };<\/p>\n

printf(“sizeof(struct str) = %d\\n”, sizeof(struct str));<\/p>\n

printf(“before f.a->s.\\n”);<\/p>\n

if (f.a->s)
\n{
\nprintf(“before printf f.a->s.\\n”);
\nprintf(f.a->s);
\nprintf(“before printf f.a->s.\\n”);
\n}<\/p>\n

return EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\n16
\n17
\n18
\n19
\n20
\n21
\n22
\n23
\n24
\n25
\n26
\n27
\n28
\n29
\n30
\n31
\n32<\/p>\n

\u53ef\u4ee5\u770b\u5230\u8fd9\u4e24\u4e2a\u7a0b\u5e8f\u867d\u7136\u90fd\u5b58\u5728\u8bbf\u95ee\u5f02\u5e38, \u4f46\u662f\u6bb5\u9519\u8bef\u7684\u4f4d\u7f6e\u5374\u4e0d\u540c<\/p>\n

\u6211\u4eec\u5c06\u4e24\u4e2a\u7a0b\u5e8f\u7f16\u8bd1\u6210\u6c47\u7f16, \u7136\u6237 diff \u67e5\u770b\u4ed6\u4eec\u7684\u6c47\u7f16\u4ee3\u7801\u6709\u4f55\u4e0d\u540c<\/p>\n

gcc -S gdb_zero_length_array.c -o gdb_test.s
\ngcc -S gdb_pzero_length_array.c -o gdb_ptest
\ndiff gdb_test.s gdb_ptest.s<\/p>\n

1c1
\n< .file “gdb_zero_length_array.c”
\n—
\n> .file “gdb_pzero_length_array.c”
\n23c23
\n< movl $4, %esi
\n—
\n> movl $16, %esi
\n30c30
\n< addq $4, %rax
\n—
\n> movq 8(%rax), %rax
\n36c36
\n< addq $4, %rax
\n—
\n> movq 8(%rax), %rax
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\n16
\n17
\n18
\n19
\n20
\n# printf(“sizeof(struct str) = %d\\n”, sizeof(struct str));
\n23c23
\n< movl $4, %esi #printf(“sizeof(struct str) = %d\\n”, sizeof(struct str));
\n—
\n> movl $16, %esi #printf(“sizeof(struct str) = %d\\n”, sizeof(struct str));
\n1
\n2
\n3
\n4
\n5
\n\u4ece64\u4f4d\u7cfb\u7edf\u4e2d, \u6c47\u7f16\u6211\u4eec\u770b\u51fa, \u53d8\u957f\u6570\u7ec4\u7ed3\u6784\u7684\u5927\u5c0f\u4e3a4, \u800c\u6307\u9488\u5f62\u5f0f\u7684\u7ed3\u6784\u5927\u5c0f\u4e3a16<\/p>\n

f.a->s
\n30c30\/36c36
\n< addq $4, %rax
\n—
\n> movq 8(%rax), %rax
\n1
\n2
\n3
\n4
\n5
\n\u53ef\u4ee5\u770b\u5230\u6709<\/p>\n

\u5bf9\u4e8e char s[0] \u6765\u8bf4, \u6c47\u7f16\u4ee3\u7801\u7528\u4e86 addq \u6307\u4ee4, addq $4, %rax<\/p>\n

\u5bf9\u4e8e char*s \u6765\u8bf4\uff0c\u6c47\u7f16\u4ee3\u7801\u7528\u4e86 movq \u6307\u4ee4, movq 8(%rax), %rax<\/p>\n

addq \u5bf9 %rax + sizeof(struct str), \u5373str\u7ed3\u6784\u7684\u672b\u5c3e\u5373\u662fchar s[0]\u7684\u5730\u5740, \u8fd9\u4e00\u6b65\u53ea\u662f\u62ff\u5230\u4e86\u5176\u5730\u5740, \u800c movq \u5219\u662f\u628a\u5730\u5740\u91cc\u7684\u5185\u5bb9\u653e\u8fdb\u53bb, \u56e0\u6b64\u6709\u65f6\u4e5f\u88ab\u7ffb\u8bd1\u4e3aleap\u6307\u4ee4, \u53c2\u89c1\u4e0b\u4e00\u5217\u5b50<\/p>\n

\u4ece\u8fd9\u91cc\u53ef\u4ee5\u770b\u5230, \u8bbf\u95ee\u6210\u5458\u6570\u7ec4\u540d\u5176\u5b9e\u5f97\u5230\u7684\u662f\u6570\u7ec4\u7684\u76f8\u5bf9\u5730\u5740, \u800c\u8bbf\u95ee\u6210\u5458\u6307\u9488\u5176\u5b9e\u662f\u76f8\u5bf9\u5730\u5740\u91cc\u7684\u5185\u5bb9(\u8fd9\u548c\u8bbf\u95ee\u5176\u5b83\u975e\u6307\u9488\u6216\u6570\u7ec4\u7684\u53d8\u91cf\u662f\u4e00\u6837\u7684)<\/p>\n

\u8bbf\u95ee\u76f8\u5bf9\u5730\u5740\uff0c\u7a0b\u5e8f\u4e0d\u4f1acrash\uff0c\u4f46\u662f\uff0c\u8bbf\u95ee\u4e00\u4e2a\u975e\u6cd5\u7684\u5730\u5740\u4e2d\u7684\u5185\u5bb9\uff0c\u7a0b\u5e8f\u5c31\u4f1acrash\u3002
\n\u6709\u65f6\u5019<\/p>\n

\/\/ 4-1.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

int main(void)
\n{<\/p>\n

char *a;
\nprintf(“%p\\n”, a);<\/p>\n

return EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n4-2.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

int main(void)
\n{<\/p>\n

char a[0];
\nprintf(“%p\\n”, a);<\/p>\n

return EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n$ diff 4-1.s 4-2.s
\n1c1
\n< .file “4-1.c”
\n—
\n> .file “4-2.c”
\n13c13
\n< subl $16, %esp
\n—
\n> subl $32, %esp
\n15c15
\n< leal 16(%esp), %eax
\n—
\n> movl 28(%esp), %eax
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n\u5bf9\u4e8e char a[0] \u6765\u8bf4, \u6c47\u7f16\u4ee3\u7801\u7528\u4e86 leal \u6307\u4ee4, leal 16(%esp), %eax<\/p>\n

\u5bf9\u4e8e char *a \u6765\u8bf4\uff0c\u6c47\u7f16\u4ee3\u7801\u7528\u4e86 movl \u6307\u4ee4, movl 28(%esp), %eax<\/p>\n

4.2 \u5730\u5740\u4f18\u5316
\n\/\/ 5-1.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

int main(void)
\n{<\/p>\n

char a[0];
\nprintf(“%p\\n”, a);<\/p>\n

char b[0];
\nprintf(“%p\\n”, b);<\/p>\n

return EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15<\/p>\n

\u7531\u4e8e0\u957f\u5ea6\u6570\u7ec4\u662f GNU C \u7684\u6269\u5c55, \u4e0d\u88ab\u6807\u51c6\u5e93\u4efb\u53ef, \u90a3\u4e48\u4e00\u4e9b\u5de7\u5999\u7f16\u5199\u7684\u8be1\u5f02\u4ee3\u7801, \u5176\u6267\u884c\u7ed3\u679c\u5c31\u662f\u4f9d\u8d56\u4e8e\u7f16\u8bd1\u5668\u548c\u4f18\u5316\u7b56\u7565\u7684\u5b9e\u73b0\u7684.<\/p>\n

\u6bd4\u5982\u4e0a\u9762\u7684\u4ee3\u7801, a\u548cb\u7684\u5730\u5740\u5c31\u4f1a\u88ab\u7f16\u8bd1\u5668\u4f18\u5316\u5230\u4e00\u5904, \u56e0\u4e3aa[0] \u548c b[0] \u5bf9\u4e8e\u7a0b\u5e8f\u6765\u8bf4\u662f\u65e0\u6cd5\u4f7f\u7528\u7684, \u8fd9\u8ba9\u6211\u4eec\u60f3\u5230\u4e86\u4ec0\u4e48?<\/p>\n

\u7f16\u8bd1\u5668\u5bf9\u4e8e\u76f8\u540c\u5b57\u7b26\u4e32\u5e38\u91cf, \u5f80\u5f80\u5730\u5740\u4e5f\u662f\u4f18\u5316\u5230\u4e00\u5904, \u51cf\u5c11\u7a7a\u95f4\u5360\u7528<\/p>\n

\/\/ 5-2.c
\n#include <stdio.h>
\n#include <stdlib.h><\/p>\n

int main(void)
\n{<\/p>\n

const char *a = “Hello”;
\nprintf(“%p\\n”, a);<\/p>\n

const char *b = “Hello”;
\nprintf(“%p\\n”, b);<\/p>\n

const char c[] = “Hello”;
\nprintf(“%p\\n”, c);<\/p>\n

return EXIT_SUCCESS;
\n}
\n1
\n2
\n3
\n4
\n5
\n6
\n7
\n8
\n9
\n10
\n11
\n12
\n13
\n14
\n15
\n16
\n17
\n18<\/p>\n

\u53c2\u8003
\n\u7ed3\u6784\u4f53\u4e2d\u7684\u6307\u9488\u4e0e\u96f6\u957f\u5ea6\u6570\u7ec4<\/p>\n

\u96f6\u957f\u5ea6\u6570\u7ec4\u7684\u5999\u7528<\/p>\n

C\u8bed\u8a00\u4e2d\u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4<\/p>\n

C\/C++ \u4e2d\u76840\u957f\u6570\u7ec4\uff08\u67d4\u6027\u6570\u7ec4\uff09<\/p>\n

GNU C\u4e2d\u7684\u96f6\u957f\u5ea6\u6570\u7ec4<\/p>\n

C\u8bed\u8a00\u53d8\u957f\u6570\u7ec4data[0]\u3010\u603b\u7ed3\u3011<\/p>\n

\u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4\u2014\u2014C\u8bed\u8a00\u7684\u975e\u6807\u51c6\u7528\u6cd5\u4e4b\u4e00<\/p>\n

\u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4\u7684size\u4e3a\u4ec0\u4e48\u4e0d\u4e00\u5b9a\u662f0\uff1f<\/p>\n

\u6709\u5173C\u8bed\u8a00\u5360\u4f4d\u7b26<\/p>\n

C\u8bed\u8a00\u6280\u5de7\u4e4b\u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4<\/p>\n

\u96f6\u957f\u5ea6\u6570\u7ec4\u4f7f\u7528<\/p>\n

\u4f7f\u7528\u96f6\u957f\u5ea6\u6570\u7ec4<\/p>\n

\u96f6\u957f\u5ea6\u6570\u7ec4<\/p>\n

C\/C++ \u4e2d\u957f\u5ea6\u4e3a0\u7684\u6570\u7ec4<\/p>\n

GCC \u4e2d\u96f6\u957f\u6570\u7ec4\u4e0e\u53d8\u957f\u6570\u7ec4<\/p>\n

\u96f6\u957f\u5ea6\u6570\u7ec4\u7684\u5999\u7528<\/p>\n

Multiple 0-length arrays have the same address?<\/p>\n

\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014\u2014
\n\u7248\u6743\u58f0\u660e\uff1a\u672c\u6587\u4e3aCSDN\u535a\u4e3b\u300cCHENG Jian\u300d\u7684\u539f\u521b\u6587\u7ae0\uff0c\u9075\u5faaCC 4.0 BY-SA\u7248\u6743\u534f\u8bae\uff0c\u8f6c\u8f7d\u8bf7\u9644\u4e0a\u539f\u6587\u51fa\u5904\u94fe\u63a5\u53ca\u672c\u58f0\u660e\u3002
\n\u539f\u6587\u94fe\u63a5\uff1ahttps:\/\/blog.csdn.net\/gatieme\/article\/details\/64131322<\/p>\n","protected":false},"excerpt":{"rendered":"

\u539f\u6587\u5730\u5740   CHENG Ji<\/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-5298","post","type-post","status-publish","format-standard","hentry","tag-02-"],"_links":{"self":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts\/5298","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=5298"}],"version-history":[{"count":0,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts\/5298\/revisions"}],"wp:attachment":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/media?parent=5298"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/categories?post=5298"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/tags?post=5298"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}