一和二
如何做一个国产数据库一 如何做一个国产数据库二
1、数据结构重新定义再次重新定义数据结构
typedef struct sdata
{
uint32_t index;
char vardata[128];
}sdata;
typedef struct sdata_index
{
uint32_t index;
uint32_t offset;
}sdata_index;
//增加的数据库上下文环境结构体
typedef struct db_context
{
char v_tablename[256];
sdata_index *v_index = NULL;
uint32_t v_tindex = 0;
uint32_t v_nindex = 0;
}db_context;
此次增加了一个数据库的db_context 结构体，包含文件名称，索引内存保存，两个index的内存保存，在增加四个api函数，以前的函数变成工具，定义tool.h 和tool.cpp.
增加api.h 和api.cpp,增加四个函数声明：
int Insert(void *data,db_context *v_context);
int Delete(void *key, db_context *v_context);
int Update(void *key, void *data, db_context *v_context);
void *Select(void *key, db_context *v_context);
今天实现Insert 函数，暂不测试，因为单元测试需要单独一个教程才行
xx xx xx xx | xx xx xx xx | xx xx xx xx – xx xx xx xx 4字节最大索引| 4字节当前索引 4bytes index 4bytes offset data … */ //2M的空间做索引 //uint32_t indext;//索引总长度 //uint32_t indexn;//索引长度,内容为x个索引 indexn v_tablename,tname); if (context->v_index == NULL) context->v_index = bfile_read_index( tname, /*filename*/ context->v_tindex, context->v_nindex ); if (context->v_index == NULL) return -1; return 0; } 2.3实现插入
整个增加的流程为：
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:root { --mermaid-font-family: "trebuchet ms", verdana, arial;}
#mermaid-svg-LnXl96nwWtNZ1uYc {
color: rgba(0, 0, 0, 0.75);
font: ;
}
打开数据库
初始化读取
读取上次索引信息
写入当次索引+偏移
写入索引量last+1
int Insert(void *data, db_context *context)
{
if (context->v_nindex v_tindex)
{
FILE * fp = fopen(context->v_tablename, "wb");
if (fp == NULL)
return -1;
fpos_t pos = 4 + 4 + (context->v_nindex) * (8);
fsetpos(fp, &pos);
//int last_index = context->v_nindex - 1;
uint32_t indexlast = context->v_index[context->v_nindex - 1].index ;
uint32_t indexinsert = indexlast + 1;
size_t n = fwrite(&indexinsert, sizeof(uint32_t), 1, fp);
if (n != sizeof(uint32_t))
{
fclose(fp);
return -1;
}
sdata *pdata = (sdata*)data;
size_t vsize = sizeof(pdata->vardata);
uint32_t datasize = vsize * indexlast;
fpos_t offset = 4 + 4 + INDEX_BYTES + datasize;
n = fwrite(&offset, sizeof(uint32_t), 1, fp);
if (n != sizeof(uint32_t))
{
fclose(fp);
return -1;
}
fsetpos(fp, &offset);
n = fwrite(data, vsize, 1, fp);
if (n != vsize)
{
fclose(fp);
return -1;
}
fpos_t index = sizeof(uint32_t);
fsetpos(fp, &index);
uint32_t newnindex = context->v_nindex + 1;
n = fwrite(&newnindex, sizeof(uint32_t), 1, fp);
if (n != sizeof(int))
{
fclose(fp);
return -1;
}
fclose(fp);
return 0;
}
return -1;
}
int Delete(void *key, db_context *v_context)
{
}
int Update(void *key, void *data, db_context *v_context)
{
}
void *Select(void *key, db_context *v_context)
{
}
上面说了，先实现增加函数，其他先不实现，也不测试，单元测试需要一个严格的定义和测试用例，此次先为增加流程的初步代码实现，有待完善。
