{"id":201223,"date":"2025-05-10T09:45:20","date_gmt":"2025-05-10T01:45:20","guid":{"rendered":"https:\/\/server.hk\/cnblog\/201223\/"},"modified":"2025-05-10T09:45:20","modified_gmt":"2025-05-10T01:45:20","slug":"redis%e7%9a%84%e5%ad%97%e7%ac%a6%e4%b8%b2%e6%98%af%e5%a6%82%e4%bd%95%e5%ae%9e%e7%8e%b0%e7%9a%84","status":"publish","type":"post","link":"https:\/\/server.hk\/cnblog\/201223\/","title":{"rendered":"Redis\u7684\u5b57\u7b26\u4e32\u662f\u5982\u4f55\u5b9e\u73b0\u7684"},"content":{"rendered":"<p><b><\/b> <\/p>\n<h1>Redis\u7684\u5b57\u7b26\u4e32\u662f\u5982\u4f55\u5b9e\u73b0\u7684<\/h1>\n<p><span style=\"cursor: pointer\"><i><\/i>\u6536\u85cf<\/span> <\/p>\n<p>\u672c\u7bc7\u6587\u7ae0\u7ed9\u5927\u5bb6\u5206\u4eab\u300aRedis\u7684\u5b57\u7b26\u4e32\u662f\u5982\u4f55\u5b9e\u73b0\u7684\u300b\uff0c\u8986\u76d6\u4e86\u6570\u636e\u5e93\u7684\u5e38\u89c1\u57fa\u7840\u77e5\u8bc6\uff0c\u5176\u5b9e\u4e00\u4e2a\u8bed\u8a00\u7684\u5168\u90e8\u77e5\u8bc6\u70b9\u4e00\u7bc7\u6587\u7ae0\u662f\u4e0d\u53ef\u80fd\u8bf4\u5b8c\u7684\uff0c\u4f46\u5e0c\u671b\u901a\u8fc7\u8fd9\u4e9b\u95ee\u9898\uff0c\u8ba9\u8bfb\u8005\u5bf9\u81ea\u5df1\u7684\u638c\u63e1\u7a0b\u5ea6\u6709\u4e00\u5b9a\u7684\u8ba4\u8bc6(B \u6570)\uff0c\u4ece\u800c\u5f25\u8865\u81ea\u5df1\u7684\u4e0d\u8db3\uff0c\u66f4\u597d\u7684\u638c\u63e1\u5b83\u3002<\/p>\n<p style=\"text-align: center\"><img decoding=\"async\" src=\"https:\/\/www.17golang.com\/uploads\/20221231\/167248174563b00bd1143fe.png\" class=\"aligncenter\"><\/p>\n<p>\u5728Redis\u8fd9\u79cd\u5185\u5b58\u6570\u636e\u5e93\u4e2d\uff0c\u7531\u4e8e\u5b57\u7b26\u4e32\u88ab\u5e7f\u6cdb\u7684\u5e94\u7528\uff0c\u5728\u8bbe\u8ba1\u5b57\u7b26\u4e32\u65f6\u57fa\u4e8e\u4ee5\u4e0b\u51e0\u70b9\u6765\u8bbe\u8ba1\uff1a<br \/> 1.\u652f\u6301\u4e30\u5bcc\u9ad8\u6548\u7684\u5b57\u7b26\u4e32\u64cd\u4f5c\uff0c\u6bd4\u5982\u8ffd\u52a0\u3001\u62f7\u8d1d\u3001\u6bd4\u8f83\u7b49\u64cd\u4f5c<br \/> 2.\u80fd\u4fdd\u5b58\u4e8c\u8fdb\u5236\u6570\u636e<br \/> 3.\u80fd\u5c3d\u53ef\u80fd\u7684\u8282\u7701\u5185\u5b58\u5f00\u9500<\/p>\n<p>\u53ef\u80fd\u4f1a\u6709\u4eba\u95ee\u4e86\uff0c\u65e2\u7136C\u8bed\u8a00\u5e93\u63d0\u4f9b\u4e86char*\u8fd9\u6837\u7684\u5b57\u7b26\u6570\u7ec4\u6765\u5b57\u7b26\u4e32\u64cd\u4f5c\u3002\u6bd4\u5982strcmp,strcat\u3002\u611f\u89c9\u5b8c\u5168\u53ef\u4ee5\u8003\u8651\u76f4\u63a5\u4f7f\u7528C\u5e93\u63d0\u4f9b\u7684\u554a\u3002C\u5e93\u5b57\u7b26\u4e32\u8fd0\u7528\u662f\u5f88\u666e\u904d\uff0c\u4f46\u662f\u4e5f\u4e0d\u662f\u6ca1\u6709\u95ee\u9898\u7684\u3002\u5b83\u9700\u8981\u9891\u7e41\u7684\u521b\u5efa\u548c\u68c0\u67e5\u7a7a\u95f4\uff0c\u8fd9\u5728\u5b9e\u9645\u9879\u76ee\u4e2d\u5176\u5b9e\u5f88\u82b1\u65f6\u95f4\u7684\u3002\u6240\u4ee5\uff0cRedis\u8bbe\u8ba1\u4e86\u7b80\u5355\u5b57\u7b26\u4e32\uff08SDS\uff0cSimple Data )\u6765\u8868\u793a\u5b57\u7b26\u4e32\u3002\u540c\u539f\u6765\u7684C\u8bed\u8a00\u76f8\u6bd4\u63d0\u5347\u4e86\u5b57\u7b26\u4e32\u7684\u64cd\u4f5c\u6548\u7387\uff0c\u800c\u4e14\u8fd8\u652f\u6301\u4e8c\u8fdb\u5236\u683c\u5f0f\u3002\u4e0b\u9762\u6211\u4eec\u5c31\u6765\u4ecb\u7ecd\u4e0bRedis\u7684\u5b57\u7b26\u4e32\u662f\u5982\u4f55\u5b9e\u73b0\u7684\u3002<\/p>\n<h2>\u4e3a\u4ec0\u4e48\u4e0d\u7528char*<\/h2>\n<p>\u5148\u6765\u770b\u770bchar*\u5b57\u7b26\u6570\u7ec4\u7684\u7ed3\u6784\uff0c\u5176\u5b9e\u5f88\u7b80\u5355\u5c31\u662f\u5f00\u8f9f\u4e00\u5757\u8fde\u7eed\u7684\u5185\u5b58\u7a7a\u95f4\u6765\u4f9d\u6b21\u5b58\u653e\u6bcf\u4e00\u4e2a\u5b57\u7b26\uff0c\u6700\u540e\u4e00\u4e2a\u5b57\u7b26\u662f&#8221;\\0&#8243;\u8868\u793a\u5b57\u7b26\u4e32\u7ed3\u675f\u3002C\u5e93\u4e2d\u7684\u5b57\u7b26\u4e32\u64cd\u4f5c\u51fd\u6570\u5c31\u662f\u901a\u8fc7\u68c0\u67e5&#8221;\\0&#8243;\u6765\u5224\u65ad\u5b57\u7b26\u4e32\u7ed3\u675f\u3002\u6bd4\u5982strlen\u51fd\u6570\u5c31\u662f\u904d\u5386\u5b57\u7b26\u6570\u7ec4\u4e2d\u7684\u6bcf\u4e00\u4e2a\u5b57\u7b26\u5e76\u8ba1\u6570\uff0c\u76f4\u5230\u9047\u5230&#8221;\\0&#8243;\u7ed3\u675f\u8ba1\u6570\uff0c\u7136\u540e\u8fd4\u56de\u8ba1\u6570\u7ed3\u679c\u3002\u4e0b\u9762\u6211\u4eec\u901a\u8fc7\u4e00\u4e2a\u4ee3\u7801\u6765\u770b\u770b&#8221;\\0&#8243;\u7ed3\u675f\u5b57\u7b26\u5bf9\u5b57\u7b26\u4e32\u957f\u5ea6\u7684\u5f71\u54cd\u3002<\/p>\n<p style=\"text-align: center\"><img decoding=\"async\" src=\"https:\/\/www.17golang.com\/uploads\/20221231\/167248174563b00bd16deba.png\" class=\"aligncenter\"><\/p>\n<p>\u8fd9\u6bb5\u4ee3\u7801\u7684\u6267\u884c\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n<p style=\"text-align: center\"><img decoding=\"async\" src=\"https:\/\/www.17golang.com\/uploads\/20221231\/167248174563b00bd1c07e2.png\" class=\"aligncenter\"><\/p>\n<p>\u8868\u793aa1\u7684\u5b57\u7b26\u957f\u5ea6\u662f2\u4e2a\u5b57\u7b26\u3002\u8fd9\u662f\u56e0\u4e3a\u5728he\u540e\u9762\u6709\u4e86&#8221;\\0&#8243;\uff0c\u6240\u4ee5\u5b57\u7b26\u4e32\u4ee5&#8221;\\0&#8243;\u8868\u793a\u7ed3\u675f\uff0c\u8fd9\u5c31\u4f1a\u4ea7\u751f\u4e00\u4e2a\u95ee\u9898\uff0c\u5982\u679c\u5b57\u7b26\u4e32\u5185\u90e8\u672c\u8eab\u5c31\u6709&#8221;\\0&#8243;,\u90a3\u4e48\u6570\u636e\u5c31\u4f1a\u88ab&#8221;\\0&#8243;\u622a\u65ad\uff0c\u800c\u8fd9\u5c31\u4e0d\u80fd<strong>\u4fdd\u5b58\u4efb\u610f\u4e8c\u8fdb\u5236\u6570\u636e<\/strong>\u4e86\u3002<\/p>\n<h2>\u4f20\u7edf\u8bbe\u8ba1\u64cd\u4f5c\u590d\u6742\u5ea6\u9ad8<\/h2>\n<p>\u9664\u4e86\u4e0a\u9762\u63d0\u5230\u7684\u4e0d\u80fd\u4fdd\u5b58\u4efb\u610f\u4e8c\u8fdb\u5236\u6570\u636e\u4ee5\u5916\uff0c\u64cd\u4f5c\u590d\u6742\u5ea6\u4e5f\u633a\u5927\u3002\u6bd4\u5982C\u8bed\u8a00\u4e2d\u7528\u5f97\u6bd4\u8f83\u666e\u904d\u7684strlen\u51fd\u6570\uff0c\u5b83\u8981\u904d\u5386\u5b57\u7b26\u6570\u7ec4\u4e2d\u7684\u6bcf\u4e00\u4e2a\u5b57\u7b26\u624d\u80fd\u5f97\u5230\u5b57\u7b26\u4e32\u957f\u5ea6\u3002\u6240\u4ee5\uff0c\u65f6\u95f4\u590d\u6742\u5ea6\u662fO(n)\u3002\u53e6\u5916\u518d\u8bf4\u4e00\u4e2a\u5e38\u7528\u51fd\u6570strcat\uff0c\u5b83\u540cstrlen\u51fd\u6570\u4e00\u6837\u5148\u904d\u5386\u5b57\u7b26\u4e32\u624d\u80fd\u5f97\u5230\u76ee\u6807\u5b57\u7b26\u4e32\u7684\u672b\u5c3e\uff0c\u800c\u4e14\u5b83\u628a\u6e90\u5b57\u7b26\u4e32\u8ffd\u52a0\u5230\u76ee\u6807\u5b57\u7b26\u4e32\u672b\u5c3e\u7684\u65f6\uff0c\u8fd8\u5f97\u786e\u8ba4\u76ee\u6807\u5b57\u7b26\u4e32\u662f\u5426\u5177\u6709\u8db3\u591f\u7684\u7a7a\u95f4\u3002\u6240\u4ee5\u5728\u8c03\u7528\u7684\u65f6\u5019\uff0c\u5f00\u53d1\u4eba\u5458\u8fd8\u8981\u4eba\u4e3a\u4fdd\u8bc1\u76ee\u6807\u5b57\u7b26\u4e32\u6709\u8db3\u591f\u7684\u53ef\u7528\u7a7a\u95f4\uff0c\u4e0d\u7136\u5c31\u9700\u8981\u52a8\u6001\u5730\u7533\u8bf7\u7a7a\u95f4\u3002\u8fd9\u6837\u4e0d\u4ec5\u65f6\u95f4\u590d\u6742\u5ea6\u9ad8\uff0c\u64cd\u4f5c\u590d\u6742\u5ea6\u4e5f\u9ad8\u4e86\u3002<\/p>\n<h2>SDS\u7684\u8bbe\u8ba1<\/h2>\n<p>Redis\u5728\u8bbe\u8ba1\u7684\u65f6\u5019\u8fd8\u662f\u5c3d\u91cf\u4fdd\u8bc1\u590d\u7528C\u6807\u51c6\u7684\u5b57\u7b26\u4e32\u64cd\u4f5c\u51fd\u6570\u7684\u3002Redis\u5728\u4fdd\u7559\u4e86\u4f7f\u7528\u5b57\u7b26\u6570\u7ec4\u6765\u4fdd\u5b58\u5b9e\u9645\u6570\u636e\u57fa\u7840\u4e0a\uff0c\u4e13\u95e8\u8bbe\u8ba1\u4e86\u4e00\u79cdSDS\u6570\u636e\u7ed3\u6784\u3002<br \/> \u9996\u5148\uff0cSDS\u7ed3\u6784\u91cc\u9762\u5305\u542b\u4e86\u4e00\u4e2a\u5b57\u7b26\u6570\u7ec4buf[],\u540c\u65f6SDS\u7ed3\u6784\u91cc\u9762\u8fd8\u5305\u542b\u4e86\u4e09\u4e2a\u5143\u6570\u636e\u3002\u5206\u522b\u662f\u5b57\u7b26\u6570\u7ec4\u73b0\u6709\u957f\u5ea6len\uff0c\u5206\u914d\u7ed9\u5b57\u7b26\u6570\u7ec4\u7684\u7a7a\u95f4\u957f\u5ea6alloc\u4ee5\u53caSDS\u7c7b\u578bflags\u3002\u5176\u4e2dlen\u548calloc\u8fd9\u4e24\u4e2a\u5143\u6570\u636e\u5b9a\u4e49\u4e86\u4e0d\u540c\u7c7b\u578b\u7684SDS\u3002SDS\u5b9a\u4e49\u4ee3\u7801\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n<pre>\ntypedef char *sds;\n\n\/* Note: sdshdr5 is never used, we just access the flags byte directly.\n * However is here to document the layout of type 5 SDS strings. *\/\nstruct __attribute__ ((__packed__)) sdshdr5 {\n    unsigned char flags; \/* 3 lsb of type, and 5 msb of string length *\/\n    char buf[];\n};\nstruct __attribute__ ((__packed__)) sdshdr8 {\n    uint8_t len; \/* used *\/\n    uint8_t alloc; \/* excluding the header and null terminator *\/\n    unsigned char flags; \/* 3 lsb of type, 5 unused bits *\/\n    char buf[];\n};\nstruct __attribute__ ((__packed__)) sdshdr16 {\n    uint16_t len; \/* used *\/\n    uint16_t alloc; \/* excluding the header and null terminator *\/\n    unsigned char flags; \/* 3 lsb of type, 5 unused bits *\/\n    char buf[];\n};\nstruct __attribute__ ((__packed__)) sdshdr32 {\n    uint32_t len; \/* used *\/\n    uint32_t alloc; \/* excluding the header and null terminator *\/\n    unsigned char flags; \/* 3 lsb of type, 5 unused bits *\/\n    char buf[];\n};\nstruct __attribute__ ((__packed__)) sdshdr64 {\n    uint64_t len; \/* used *\/\n    uint64_t alloc; \/* excluding the header and null terminator *\/\n    unsigned char flags; \/* 3 lsb of type, 5 unused bits *\/\n    char buf[];\n};<\/pre>\n<p>\u7528\u4e2a\u56fe\u6765\u8868\u793a\u4e00\u4e0b<\/p>\n<p style=\"text-align: center\"><img decoding=\"async\" src=\"https:\/\/www.17golang.com\/uploads\/20221231\/167248174663b00bd22c0c4.png\" class=\"aligncenter\"><\/p>\n<p>\u4ee3\u7801\u4e2d\u5b9a\u4e49\u4e86\u4e00\u4e2a\u522b\u540d<\/p>\n<pre>\ntypedef char *sds;<\/pre>\n<p>\u6240\u4ee5SDS\u672c\u8d28\u8fd8\u662f\u5b57\u7b26\u6570\u7ec4\uff0c\u53ea\u662f\u5728\u5b57\u7b26\u6570\u7ec4\u57fa\u7840\u4e0a\u589e\u52a0\u4e86\u989d\u5916\u7684\u5143\u6570\u636e\uff0cRedis\u5728\u4f7f\u7528\u5b57\u7b26\u6570\u7ec4\u65f6\u76f4\u63a5\u4f7f\u7528sds\u8fd9\u4e2a\u522b\u540d\u3002<\/p>\n<h2>SDS\u7684\u9ad8\u6548\u64cd\u4f5c<\/h2>\n<h3>\u521b\u5efasds<\/h3>\n<p>Redis\u8c03\u7528sdsnewlen\u51fd\u6570\u521b\u5efasds\u3002\u6211\u4eec\u4ee5sedsnewlen\u4e3e\u4f8b\uff0c\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n<pre>\nhisds sdsnewlen(const void *init, size_t initlen) {\n   \/\/\u6307\u5411SDS\u7ed3\u6784\u7684\u6307\u9488\n    void *sh;\n    \/\/sds\u7c7b\u578b\u53d8\u91cf,\u5c31\u662fchar*\u7684\u522b\u540d\n    sds s;\n    \/\/\u6839\u636e\u5927\u5c0f\u83b7\u53d6SDS\u7684\u7c7b\u578b\n    char type = hi_sdsReqType(initlen);\n    \/* Empty strings are usually created in order to append. Use type 8\n     * since type 5 is not good at this. *\/\n    if (type == SDS_TYPE_5 &amp;&amp; initlen == 0) type = SDS_TYPE_8;\n    int hdrlen = sdsHdrSize(type);\n    unsigned char *fp; \/* flags pointer. *\/\n\n     \/\/\u4e3a\u65b0\u521b\u5efa\u7684sds\u7ed3\u6784\u5206\u914d\u5185\u5b58\n    sh = s_malloc(hdrlen+initlen+1);\n    if (sh == NULL) return NULL;\n    if (!init)\n        memset(sh, 0, hdrlen+initlen+1);\n    \n    \/\/\u6307\u5411SDS\u7ed3\u6784\u4f53\u4e2d\u7684buf\u6570\u7ec4,sh\u6307\u5411SDS\u7ed3\u6784\u7684\u8d77\u59cb\u4f4d\u7f6e\uff0chdrlen\u8868\u793a\u5143\u6570\u636e\u7684\u957f\u5ea6    \n    s = (char*)sh+hdrlen;\n    fp = ((unsigned char*)s)-1;\n    \/\/\u6839\u636e\u7c7b\u578b\u521d\u59cb\u5316len,alloc\n    switch(type) {\n        case SDS_TYPE_5: {\n            *fp = type | (initlen len = initlen;\n            sh-&gt;alloc = initlen;\n            *fp = type;\n            break;\n        }\n        case SDS_TYPE_16: {\n            SDS_HDR_VAR(16,s);\n            sh-&gt;len = initlen;\n            sh-&gt;alloc = initlen;\n            *fp = type;\n            break;\n        }\n        case SDS_TYPE_32: {\n            SDS_HDR_VAR(32,s);\n            sh-&gt;len = initlen;\n            sh-&gt;alloc = initlen;\n            *fp = type;\n            break;\n        }\n        case SDS_TYPE_64: {\n            SDS_HDR_VAR(64,s);\n            sh-&gt;len = initlen;\n            sh-&gt;alloc = initlen;\n            *fp = type;\n            break;\n        }\n    }\n    if (initlen &amp;&amp; init)\n    \/\/\u5c06\u5b57\u7b26\u4e32\u62f7\u8d1d\u7ed9sds\u53d8\u91cfs\n        memcpy(s, init, initlen);\n     \/\/\u5b57\u7b26\u4e32\u53d8\u91cf\u672b\u5c3e\u6dfb\u52a0\"\\0\"\u8868\u793a\u5b57\u7b26\u4e32\u7ed3\u675f  \n    s[initlen] = '\\0';\n    return s;\n}<\/pre>\n<p>\u8be5\u51fd\u6570\u4e3b\u8981\u6267\u884c\u8fc7\u7a0b\u5982\u4e0b\uff1a<br \/> 1.\u6839\u636e\u521d\u59cb\u5316\u957f\u5ea6\u83b7\u53d6SDS\u7c7b\u578b\u3002\u5982\u679c\u521d\u59cb\u5316\u957f\u5ea6initlen\u4e3a0\uff0c\u4e00\u822c\u88ab\u8ba4\u4e3a\u662f\u8981\u6267\u884cappend\u64cd\u4f5c\uff0c\u8bbe\u7f6eSDS\u7c7b\u578b\u4e3aSDS_TYPE_8<br \/> 2.\u4e3a\u65b0\u521b\u5efa\u7684SDS\u7ed3\u6784\u5206\u914d\u5185\u5b58\uff0c\u5185\u5b58\u7a7a\u95f4\u4e3a\u5143\u6570\u636e\u957f\u5ea6+buf\u957f\u5ea6+\u5b57\u7b26\u4e32\u6700\u540e\u7684\u7ed3\u675f\u7b26&#8221;\\0&#8243;\u3002<br \/> 3.\u6839\u636eSDS\u7c7b\u578b\u53bb\u521d\u59cb\u5316\u5143\u6570\u636elen\u548calloc<br \/> 4.\u5c06\u5b57\u7b26\u4e32\u62f7\u8d1d\u7ed9sds<\/p>\n<h3>\u5b57\u7b26\u6570\u7ec4\u62fc\u63a5<\/h3>\n<p>\u7531\u4e8esds\u7ed3\u6784\u4e2d\u8bb0\u5f55\u4e86\u5360\u7528\u7684\u7a7a\u95f4\u548c\u88ab\u5206\u914d\u7684\u7a7a\u95f4\uff0c\u6240\u4ee5\u5b83\u6bd4\u4f20\u7edfC\u8bed\u8a00\u7684\u5b57\u7b26\u4e32\u6548\u7387\u66f4\u9ad8\u3002\u4e0b\u9762\u6211\u4eec\u901a\u8fc7Redis\u7684\u5b57\u7b26\u4e32\u8ffd\u52a0\u51fd\u6570sdscatlen\u6765\u770b\u4e00\u770b\u3002\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n<pre>\nsds sdscatlen(sds s, const void *t, size_t len) {\n\/\/\u83b7\u53d6\u76ee\u6807\u5b57\u7b26\u4e32\u7684\u957f\u5ea6 \n size_t curlen = sdslen(s);\n\/\/\u6839\u636e\u8ffd\u52a0\u957f\u5ea6\u548c\u76ee\u6807\u5b57\u7b26\u4e32\u957f\u5ea6\u5224\u65ad\u662f\u5426\u9700\u8981\u589e\u52a0\u65b0\u7684\u7a7a\u95f4\n  s = sdsMakeRoomFor(s,len);\n  if (s == NULL) return NULL;\n  \/\/\u5c06\u6e90\u5b57\u7b26\u4e32t\u4e2dlen\u957f\u5ea6\u7684\u6570\u636e\u62f7\u8d1d\u5230\u76ee\u6807\u5b57\u7b26\u4e32\u5c3e\u90e8\n  memcpy(s+curlen, t, len);\n  \/\/\u8bbe\u7f6e\u76ee\u6807\u5b57\u7b26\u4e32\u7684\u6700\u65b0\u957f\u5ea6\n  sdssetlen(s, curlen+len);\n  \/\/\u62f7\u8d1d\u5b8c\u6210\u540e\uff0c\u5728\u5b57\u7b26\u4e32\u7ed3\u5c3e\u52a0\u4e0a\"\\0\"\n  s[curlen+len] = '\\0';\n  return s;\n}\n<\/pre>\n<p>\u8fd9\u4e2a\u51fd\u6570\u6709\u4e09\u4e2a\u53c2\u6570\u5206\u522b\u662f\u76ee\u6807\u5b57\u7b26\u4e32s,\u6e90\u5b57\u7b26\u4e32t\u548c\u8981\u8ffd\u52a0\u7684\u957f\u5ea6len\u3002\u8fd9\u4e2a\u4ee3\u7801\u6267\u884c\u8fc7\u7a0b\u5982\u4e0b\uff1a<br \/> 1.\u9996\u5148\u83b7\u53d6\u76ee\u6807\u5b57\u7b26\u4e32\u7684\u957f\u5ea6\uff0c\u7136\u540e\u8c03\u7528sdsMakeRoomFor\u51fd\u6570\u5224\u65ad\u662f\u5426\u8981\u7ed9\u76ee\u6807\u5b57\u7b26\u4e32\u6dfb\u52a0\u65b0\u7684\u7a7a\u95f4\uff0c\u8fd9\u6837\u5c31\u53ef\u4ee5\u4fdd\u8bc1\u76ee\u6807\u5b57\u7b26\u4e32\u6709\u8db3\u591f\u7684\u7a7a\u95f4\u8ffd\u52a0\u5b57\u7b26\u4e32<br \/> 2.\u5728\u4fdd\u8bc1\u4e86\u6709\u8db3\u591f\u7a7a\u95f4\u53ef\u4ee5\u8ffd\u52a0\u5b57\u7b26\u4e32\u540e\uff0c\u5c06\u6e90\u5b57\u7b26\u4e32\u4e2d\u6307\u5b9a\u957f\u5ea6len\u7684\u6570\u636e\u8ffd\u52a0\u5230\u76ee\u6807\u5b57\u7b26\u4e32<br \/> 3.\u8bbe\u7f6e\u76ee\u6807\u5b57\u7b26\u4e32\u7684\u6700\u65b0\u957f\u5ea6<\/p>\n<h3>\u957f\u5ea6\u83b7\u53d6<\/h3>\n<p>\u4ee3\u7801\u4e2d\uff0c\u51fd\u6570sdslen\u8bb0\u5f55\u4e86\u5b57\u7b26\u6570\u7ec4\u7684\u4f7f\u7528\u957f\u5ea6\uff0c\u4e0d\u7528\u540cC\u5e93\u4e00\u6837\u904d\u5386\u5b57\u7b26\u4e32\u4e86\uff0c\u8fd9\u6837\u53ef\u4ee5\u5927\u5927\u964d\u4f4e\u4e86\u64cd\u4f5c\u4f7f\u7528\u5b57\u7b26\u4e32\u7684\u5f00\u9500\u3002\u8be5\u51fd\u6570\u7684\u4ee3\u7801\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n<pre>\nstatic inline size_t sdslen(const sds s) {\n    unsigned char flags = s[-1];\n    switch(flags&amp;SDS_TYPE_MASK) {\n        case SDS_TYPE_5:\n            return SDS_TYPE_5_LEN(flags);\n        case SDS_TYPE_8:\n            return SDS_HDR(8,s)-&gt;len;\n        case SDS_TYPE_16:\n            return SDS_HDR(16,s)-&gt;len;\n        case SDS_TYPE_32:\n            return SDS_HDR(32,s)-&gt;len;\n        case SDS_TYPE_64:\n            return SDS_HDR(64,s)-&gt;len;\n    }\n    return 0;\n}\n<\/pre>\n<p>\u8fd9\u6837\u65f6\u95f4\u590d\u6742\u5ea6\u76f4\u63a5\u964d\u5230\u4e86O(1)\u3002\u8fd9\u4e2a\u51fd\u6570\u6709\u4e00\u4e2a\u9a9a\u64cd\u4f5c\uff0c\u901a\u8fc7s[-1]\u83b7\u53d6\u5230flags\uff0c\u7136\u540e\u8c03\u7528SDS_HDR\u5b8f\u51fd\u6570\u3002\u6211\u4eec\u6765\u770b\u4e0b\u8fd9\u4e2a\u5b8f\u51fd\u6570\u5b9a\u4e49<\/p>\n<pre>\n#define SDS_HDR(T,s) ((struct sdshdr##T *)((s)-(sizeof(struct sdshdr##T))))\n<\/pre>\n<p>\u5176\u4e2d##\u7528\u6765\u5c06\u4e24\u4e2atoken\u8fde\u63a5\u4e3a\u4e00\u4e2atoken\uff0c\u6240\u4ee5\u52a0\u4e0a\u53c2\u6570\u5c06\u5728\u9884\u7f16\u8bd1\u9636\u6bb5\u5c06\u88ab\u66ff\u6362\u5982\u4e0b<\/p>\n<pre>\nSDS_HDR(8,s);\n((struct sdshdr8 *)((s)-(sizeof(struct sdshdr8))))\n<\/pre>\n<p>\u5b57\u7b26\u6570\u7ec4\u5730\u5740\u51cf\u53bb\u7ed3\u6784\u4f53\u7684\u5927\u5c0f\uff0c\u5c31\u80fd\u83b7\u53d6\u5230\u7ed3\u6784\u4f53\u7684\u9996\u5730\u5740\uff0c\u7136\u540e\u76f4\u63a5\u8bbf\u95eelen\u5c5e\u6027\u3002<\/p>\n<h3>\u9884\u5206\u914d\u5185\u5b58\u7a7a\u95f4<\/h3>\n<p>\u6b64\u5916\uff0c\u5728\u4ee3\u7801\u4e2d\u8fd8\u4f7f\u7528\u4e86sdsMakeRoomFor\u51fd\u6570\uff0c\u5b83\u5728\u62fc\u63a5\u5b57\u7b26\u4e32\u4e4b\u524d\u4f1a\u68c0\u67e5\u662f\u5426\u9700\u8981\u6269\u5bb9\uff0c\u5982\u679c\u9700\u8981\u6269\u5bb9\u5219\u4f1a\u9884\u5206\u914d\u7a7a\u95f4\u3002\u8fd9\u4e00\u8bbe\u8ba1\u7684\u597d\u5904\u5c31\u662f\u907f\u514d\u4e86\u5f00\u53d1\u4e2d\u5fd8\u8bb0\u7ed9\u76ee\u6807\u5b57\u7b26\u4e32\u6269\u5bb9\u800c\u5bfc\u81f4\u64cd\u4f5c\u5931\u8d25\u3002\u6bd4\u5982strcpy(char* dst, const char* dst),\u5982\u679csrc\u957f\u5ea6\u5927\u4e8e\u4e86dst\u7684\u957f\u5ea6\uff0c\u53c8\u6ca1\u6709\u505a\u68c0\u67e5\u5c31\u4f1a\u906d\u6210\u5185\u5b58\u6ea2\u51fa\u3002\u4ee3\u7801\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n<pre>\nsds sdsMakeRoomFor(sds s, size_t addlen) {\n    void *sh, *newsh;\n    \/\/\u83b7\u53d6SDS\u76ee\u524d\u53ef\u7528\u7684\u7a7a\u95f4\n    size_t avail = sdsavail(s);\n    size_t len, newlen;\n    char type, oldtype = s[-1] &amp; SDS_TYPE_MASK;\n    int hdrlen;\n    size_t usable;\n\n    \/\/\u7a7a\u4f59\u7a7a\u95f4\u8db3\u591f\uff0c\u65e0\u9700\u6269\u5c55\n    if (avail &gt;= addlen) return s;\n\n    len = sdslen(s);\n    sh = (char*)s-sdsHdrSize(oldtype);\n    newlen = (len+addlen);\n    assert(newlen &gt; len);   \/* Catch size_t overflow *\/\n    \/\/\u5982\u679c\u65b0\u7684\u5b57\u7b26\u6570\u7ec4\u957f\u5ea6\u5c0f\u4e8eSDS_MAX_PREALLOC\n    \/\/\u5206\u914d2\u500d\u6240\u9700\u957f\u5ea6\n    if (newlen  len);  \/* Catch size_t overflow *\/\n    if (oldtype==type) {\n        newsh = s_realloc_usable(sh, hdrlen+newlen+1, &amp;usable);\n        if (newsh == NULL) return NULL;\n        s = (char*)newsh+hdrlen;\n    } else {\n        \/ \/\u5982\u679c\u5934\u90e8\u5927\u5c0f\u53d1\u751f\u53d8\u5316\u53ea\u9700\u8981\u5c06\u5b57\u7b26\u6570\u7ec4\u5411\u524d\u79fb\uff0c\u4e0d\u4f7f\u7528realloc\n        newsh = s_malloc_usable(hdrlen+newlen+1, &amp;usable);\n        if (newsh == NULL) return NULL;\n        memcpy((char*)newsh+hdrlen, s, len+1);\n        s_free(sh);\n        s = (char*)newsh+hdrlen;\n        s[-1] = type;\n        sdssetlen(s, len);\n    }\n    usable = usable-hdrlen-1;\n    if (usable &gt; sdsTypeMaxSize(type))\n        usable = sdsTypeMaxSize(type);\n     \/\/\u66f4\u65b0SDS\u5bb9\u91cf  \n    sdssetalloc(s, usable);\n    return s;\n}\n<\/pre>\n<p>\u5176\u4e2dSDS_MAX_PREALLOC\u7684\u957f\u5ea6\u4e3a1024*1024<\/p>\n<pre>\n#define SDS_MAX_PREALLOC (1024*1024)\n<\/pre>\n<h2>\u8282\u7701\u5185\u5b58\u7684\u8bbe\u8ba1<\/h2>\n<p>\u524d\u9762\u8bb2SDS\u7ed3\u6784\u7684\u65f6\u5019\u63d0\u5230\u8fc7\u5b83\u6709\u4e00\u4e2a\u5143\u6570\u636eflag\uff0c\u8868\u793a\u5b57\u7b26\u4e32\u7c7b\u578b\u3002SDS\u4e00\u5171\u67095\u4e2d\u7c7b\u578b\uff0c\u5b83\u4eec\u5206\u522b\u662fsdshdr5,sdshdr8,sdshdr16,sdshdr32\u548csdshdr64\u3002\u8fd9\u4e94\u79cd\u7684\u4e3b\u8981\u533a\u522b\u662f\u5b83\u4eec\u5b57\u7b26\u6570\u7ec4\u7684\u73b0\u6709\u957f\u5ea6len\u548c\u5206\u914d\u7a7a\u95f4alloc\u7684\u4e0d\u540c\u3002<br \/> \u90a3\u4e48\u6211\u4eec\u5c31\u4ee5sdshdr16\u4e3a\u4f8b\uff0c\u5b83\u7684\u5b9a\u4e49\u5982\u4e0b<\/p>\n<pre>\nstruct __attribute__ ((__packed__)) sdshdr16 {\n    uint16_t len; \/* used *\/\n    uint16_t alloc; \/* excluding the header and null terminator *\/\n    unsigned char flags; \/* 3 lsb of type, 5 unused bits *\/\n    char buf[];\n};\n<\/pre>\n<p>\u6211\u4eec\u53ef\u4ee5\u770b\u5230\u73b0\u6709\u957f\u5ea6len\u548c\u5df2\u5206\u914d\u7a7a\u95f4alloc\u90fd\u662fuint16_t\u7c7b\u578b\uff0cuint16_t\u662f16\u4f4d\u65e0\u7b26\u53f7\u6574\u578b\uff0c\u4f1a\u5360\u75282\u4e2a\u5b57\u8282\u3002\u5f53\u5b57\u7b26\u4e32\u7c7b\u578b\u662fsdshdr16\u7684\u65f6\u5019\u5b83\u5305\u542b\u7684\u5b57\u7b26\u6570\u7ec4\u957f\u5ea6\u6700\u5927\u4e3a2^16-1\u5b57\u8282\u3002\u800c\u5bf9\u4e8e\u5176\u5b83\u4e09\u79cdsdshdr8,sdshdr32\u548csdshdr64\uff0c\u4ee5\u6b64\u7c7b\u63a8\u5b83\u4eec\u7684\u7c7b\u578b\u5c31\u5206\u522b\u662fuin8_t\uff0cuin32_t\u548cuint64_t\uff0clen\u548calloc\u8fd9\u4e24\u4e2a\u5143\u6570\u636e\u5360\u7528\u7684\u7a7a\u95f4\u5206\u522b\u662f1\u5b57\u8282\u30014\u5b57\u8282\u548c8\u5b57\u8282\u3002<br \/> \u5b9e\u9645\u4e0a\uff0c\u8bbe\u8ba1\u4e0d\u540c\u7684\u7ed3\u6784\u5934\u7684\u76ee\u7684\u662f\u4e3a\u4e86\u7075\u6d3b\u4fdd\u5b58\u4e0d\u540c\u5927\u5c0f\u7684\u5b57\u7b26\u4e32\uff0c\u4ece\u800c\u6709\u6548\u5730\u8282\u7701\u5185\u5b58\u7a7a\u95f4\u3002\u5728\u4fdd\u5b58\u4e0d\u540c\u5927\u5c0f\u7684\u5b57\u7b26\u4e32\u65f6\uff0c\u7ed3\u6784\u5934\u5360\u7528\u7684\u5185\u5b58\u7a7a\u95f4\u4e5f\u4e0d\u4e00\u6837\uff0c\u8fd9\u6837\u4e00\u6765\u4fdd\u5b58\u5c0f\u5b57\u7b26\u4e32\u65f6\uff0c\u5360\u7528\u7684\u7a7a\u95f4\u4e5f\u4f1a\u6bd4\u8f83\u5c0f\u3002<br \/> \u9664\u4e86\u8bbe\u8ba1\u4e0d\u540c\u7c7b\u578b\u7684\u7ed3\u6784\u5934\u4ee5\u5916\uff0cRedis\u8fd8\u4f7f\u7528\u7f16\u8bd1\u4f18\u5316\u6765\u8282\u7701\u5185\u5b58\u7a7a\u95f4\u3002\u6bd4\u5982\u4e0a\u9762sdshdr16\u7684\u4ee3\u7801\u4e2d\u5c31\u6709__attribute__ ((<strong>packed<\/strong>))\uff0c\u5b83\u7684\u76ee\u7684\u662f\u544a\u8bc9\u7f16\u8bd1\u5668\u91c7\u7528\u7d27\u51d1\u7684\u65b9\u5f0f\u5206\u914d\u5185\u5b58\uff0c\u9ed8\u8ba4\u60c5\u51b5\u4e0b\u7f16\u8bd1\u5668\u4f1a\u6309\u716716\u5b57\u8282\u7684\u5bf9\u9f50\u65b9\u5f0f\u7ed9\u53d8\u91cf\u5206\u914d\u5185\u5b58\u3002\u4e5f\u5c31\u662f\u8bf4\u4e00\u4e2a\u53d8\u91cf\u6ca1\u6709\u523016\u4e2a\u5b57\u8282\uff0c\u7f16\u8bd1\u5668\u4e5f\u4f1a\u7ed9\u5b83\u5206\u914d16\u4e2a\u5b57\u8282\u3002<br \/> \u6211\u4eec\u6765\u4e3e\u4e2a\u4f8b\u5b50<\/p>\n<pre>\n#include \n   \n    \n#include \n    \n      using namespace std; typedef struct MyStruct { char a; int b; } MyStruct; int main() { cout \n     <p>\u867d\u7136char\u5360\u75281\u4e2a\u5b57\u8282\uff0cint\u5360\u75284\u4e2a\u5b57\u8282\uff0c\u4f46\u662f\u6253\u5370\u51fa\u6765\u662f8\uff0c\u8fd9\u6837\u591a\u51fa\u6765\u76843\u4e2a\u5b57\u8282\u767d\u767d\u6d6a\u8d39\u6389\u4e86\u3002\u73b0\u5728\u6211\u4eec\u8fd0\u7528__attribute__ ((<strong>packed<\/strong>))\u5c5e\u6027\u5b9a\u4e49\u7ed3\u6784\u4f53\uff0c\u5c31\u53ef\u4ee5\u5b9e\u9645\u5360\u7528\u591a\u5c11\u5b57\u8282\uff0c\u7f16\u8bd1\u5668\u5c31\u5206\u914d\u591a\u5c11\u7a7a\u95f4\u3002\u6211\u4eec\u628a\u521a\u624d\u4ee3\u7801\u4fee\u6539\u4e00\u4e0b\u52a0\u4e0a\u8fd9\u4e2a\u5c5e\u6027\u3002\u4ee3\u7801\u5982\u4e0b<\/p> \n     <pre>\n#include \n      \n       \n#include \n       \n         using namespace std; typedef struct MyStruct { char a; int b; } __attribute__ ((__packed__))MyStruct; int main() { cout \n        <p>\u8fd0\u884c\u8fd9\u6bb5\u4ee3\u7801\uff0c\u7ed3\u679c\u5c31\u53d8\u4e3a5\u4e86\uff0c\u8868\u793a\u7f16\u8bd1\u5668\u7528\u4e86\u7d27\u51d1\u578b\u7684\u5185\u5b58\u5206\u914d\u3002\u5728\u5f00\u53d1\u8fc7\u7a0b\u4e2d\uff0c\u4e3a\u4e86\u8282\u7701\u5185\u5b58\u5f00\u9500\u5c31\u53ef\u4ee5\u8003\u8651\u628a__attribute__ ((<strong>packed<\/strong>))\u8fd9\u4e2a\u5c5e\u6027\u8fd0\u7528\u8d77\u6765\u3002<\/p> \n        \n       \n      <\/pre>\n","protected":false},"excerpt":{"rendered":"<p>Redis\u7684\u5b57\u7b26\u4e32\u662f\u5982\u4f55\u5b9e\u73b0\u7684 &#46;&#46;&#46;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-201223","post","type-post","status-publish","format-standard","hentry","category-database"],"_links":{"self":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/201223","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/comments?post=201223"}],"version-history":[{"count":0,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/posts\/201223\/revisions"}],"wp:attachment":[{"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/media?parent=201223"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/categories?post=201223"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/server.hk\/cnblog\/wp-json\/wp\/v2\/tags?post=201223"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}