解析
sdshdr8
#pragma pack(1)
struct __attribute__((__packed__)) sdshdr8{ uint8_t len; /* used */
uint8_t alloc; /* excluding the header and null terminator */
unsigned char flags; /* 3 lsb of type, 5 unused bits */
char buf[];
};1字节对齐，sdshdr8结构体有3个字节，即sizeof(sdshdr8) = 3。
zmalloc
Malloc一块内存时_mptr，前sizeof(size_t)字节，存储开辟内存的大小，从开辟内存_mptr + sizeof(size_t)为用户提供的数据空间。
zfree
对于 zmalloc开辟的一块数据 _fptr，释放时需要获取内存的首地址，即_fptr - sizeof(size_t)。
sdshdr结构体与robj结构体结合使用
int len = 5;const char* ptr = "hello";robj* o = (robj*)zmalloc(sizeof(robj) + sizeof(struct sdshdr8) + len + 1);struct sdshdr8* sh = (sdshdr8*)(o + 1);o->type = 0;o->encoding = 8;o->ptr = sh +1;o->refcount = 1;sh->len = len;sh->alloc = len;sh->flags = 1;memcpy(sh->buf, ptr, len);sh->buf[len] = '\0';sds s = (sds)o->ptr;size_t slen;//slen = SDS_HDR(8, s)->len;slen = ((struct sdshdr8*)((s)-(sizeof(struct sdshdr8))))->len;zfree(o);测试源码
#include <iostream>typedef signed char int8_t;
typedef short int16_t;
typedef int int32_t;
typedef long long int64_t;
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;
typedef unsigned long long uint64_t;#ifdef HAVE_MALLOC_SIZE
#define PREFIX_SIZE (0)
#else
#if defined(__sun) || defined(__sparc) || defined(__sparc__)
#define PREFIX_SIZE (sizeof(long long))
#else
#define PREFIX_SIZE (sizeof(size_t))
#endif
#endif#pragma pack(1)
typedef struct _su
{int32_t val;double dvalue;//void* key;
}su;#define ZIPLIST_BYTES(zl) (*((uint32_t*)(zl)))
#define SDS_TYPE_MASK 7#ifdef _MSC_VER
#define __attribute__(x)
#endiftypedef char* sds;
#pragma pack(1)
struct __attribute__((__packed__)) sdshdr5 {unsigned char flags; /* 3 lsb of type, and 5 msb of string length */char buf[];
};
#pragma pack(1)
struct __attribute__((__packed__)) sdshdr8 {uint8_t len; /* used */uint8_t alloc; /* excluding the header and null terminator */unsigned char flags; /* 3 lsb of type, 5 unused bits */char buf[];
};
#pragma pack(1)
struct __attribute__((__packed__)) sdshdr16 {uint16_t len; /* used */uint16_t alloc; /* excluding the header and null terminator */unsigned char flags; /* 3 lsb of type, 5 unused bits */char buf[];
};
#pragma pack(1)
struct __attribute__((__packed__)) sdshdr32 {uint32_t len; /* used */uint32_t alloc; /* excluding the header and null terminator */unsigned char flags; /* 3 lsb of type, 5 unused bits */char buf[];
};
#pragma pack(1)
struct __attribute__((__packed__)) sdshdr64 {uint64_t len; /* used */uint64_t alloc; /* excluding the header and null terminator */unsigned char flags; /* 3 lsb of type, 5 unused bits */char buf[];
};#pragma pack(1)
struct __attribute__((__packed__)) sdsdouble {uint64_t len; /* used */unsigned char flags; /* 3 lsb of type, 5 unused bits */char buf[];
};#define SDS_TYPE_5 0
#define SDS_TYPE_8 1
#define SDS_TYPE_16 2
#define SDS_TYPE_32 3
#define SDS_TYPE_64 4
#define SDS_TYPE_MASK 7
#define SDS_TYPE_BITS 3
#define SDS_HDR_VAR(T,s) struct sdshdr##T *sh = (struct sdshdr##T *)((s)-(sizeof(struct sdshdr##T)));
#define SDS_HDR(T,s) ((struct sdshdr##T *)((s)-(sizeof(struct sdshdr##T))))
#define SDS_TYPE_5_LEN(f) ((f)>>SDS_TYPE_BITS)#define GET_INT32_VALUE(_ptr, _offet) (*(int32_t*)_ptr + _offet);#define GET_DOUBLE_VALUE(val ,_ptr, _offet)\
do \
{\memcpy((void*)&val, _ptr + _offet, sizeof(double));\
} while (0);\#define SDS_HDR(T,s) ((struct sdshdr##T *)((s)-(sizeof(struct sdshdr##T))))//前4个字节，保存长度
void* zmalloc(size_t size) {void* ptr = malloc(size + PREFIX_SIZE);*((size_t*)ptr) = size;return (char*)ptr + PREFIX_SIZE;
}static inline int sdsHdrSize(char type) {switch (type & SDS_TYPE_MASK) {case SDS_TYPE_5:return sizeof(struct sdshdr5);case SDS_TYPE_8:return sizeof(struct sdshdr8);case SDS_TYPE_16:return sizeof(struct sdshdr16);case SDS_TYPE_32:return sizeof(struct sdshdr32);case SDS_TYPE_64:return sizeof(struct sdshdr64);}return 0;
}typedef struct redisObject {unsigned type : 4;unsigned encoding : 4;int refcount;void* ptr;
} robj;void sdsfree(sds s) {if (s == NULL) return;int n = s[-1] & SDS_TYPE_MASK;//free((char*)s - sizeof(struct sdshdr8));free((char*)s - sdsHdrSize(s[-1]));
}void zfree(void* ptr) {void* realptr;realptr = (char*)ptr - PREFIX_SIZE;free(realptr);
}int main()
{std::cout << "Hello World!\n";/**************************数值数据解析****************************************/su _s;_s.val = 2; _s.dvalue = 0.6666f;char* _ptr = (char*)malloc(sizeof(su));memcpy(_ptr, (void*)&_s, sizeof(su));int32_t _val = (*(int32_t*)_ptr);_val = GET_INT32_VALUE(_ptr, 0);double _dval;GET_DOUBLE_VALUE(_dval, _ptr, sizeof(int32_t));//memcpy((void*)&_dval, _ptr + sizeof(int32_t),sizeof(double));// double _dval = (*(double*)_ptr + sizeof(int32_t));int _len = sizeof(sdsdouble);/******************************************************************//***************************sdshdr8 结构体使用操作***************************************/int len = 5;const char* ptr = "hello";robj* o = (robj*)zmalloc(sizeof(robj) + sizeof(struct sdshdr8) + len + 1);struct sdshdr8* sh = (sdshdr8*)(o + 1);o->type = 0;o->encoding = 8;o->ptr = sh +1;o->refcount = 1;sh->len = len;sh->alloc = len;sh->flags = 1;memcpy(sh->buf, ptr, len);sh->buf[len] = '\0';sds s = (sds)o->ptr;size_t slen;//slen = SDS_HDR(8, s)->len;slen = ((struct sdshdr8*)((s)-(sizeof(struct sdshdr8))))->len;zfree(o);/******************************************************************/return 0;
}