dtostr，一个double to string，好纠结。

看看本身刚入门时写的东西！竟然还用了一年！！要留下来，证实本身的成长。

char * tr_dtostr(double value, int declen)

{     char * pstring = NULL;     int64_t intval = 0;     uint16_t effenum = 0;     uint16_t renum = 0;     uint32_t i = 0;     int64_t longnum = 0;     uint64_t plongnum = 0;     int64_t anum = 0;     int64_t bnum = 0;     //有效位长度若是<0 或 >19位则等于19位     if (declen <= 0 || declen > 19)     {         declen = 19;     }     pstring = (char *) malloc(21);     memset(pstring, 0, 21);     intval = (int64_t) value;//获取整数值     if (value < 0.0)//肯定负值     {         if (intval == 0)//肯定整数位为0         {             char chnum[21] = {             0             };             sprintf(pstring, "%s", "-");             sprintf(chnum, "%lld", intval);             strcat(pstring, chnum);             strcat(pstring, ".");//存入“-0.”         }         else//整数位不为0存入“负数.”         {             sprintf(pstring, "%lld", intval);             strcat(pstring, ".");         }         if (intval != 0)//若是         {             renum = strlen(pstring) - 2;         }         else         {             renum = strlen(pstring) - 3;         }         effenum = 15 - renum;     }     else     {         sprintf(pstring, "%lld", intval);         strcat(pstring, ".");         if (intval != 0)         {             renum = strlen(pstring) - 1;         }         else         {             renum = strlen(pstring) - 2;         }         effenum = 15 - renum;     }     if (intval == 0)     {         anum = (value) * pow(10,effenum);         bnum = intval * pow(10,effenum);         longnum = anum - bnum;         plongnum = labs(longnum);         if (value > 0.0)         {             anum = (value + 1) * pow(10,effenum);         }         else if (value < 0.0)         {             anum = (value - 1) * pow(10,effenum);         }         else if (value == 0)         {             sprintf(pstring, "%s", "0");             return pstring;         }     }     else     {         anum = value * pow(10,effenum);         bnum = intval * pow(10,effenum);         longnum = anum - bnum;         plongnum = labs(longnum);     }     if (plongnum == 0)     {         //小数部位全为0         pstring[strlen(pstring)-1] = 0;         return pstring;     }     else     {         char chnum[20] = {         0         };         uint8_t sursavelen = 0;//剩余应该保存个数         int invallen = 0;//小数部位转为整数后的大小         int vallen = 0; //小数部位非零数的个数（包括非零数中间0的个数）         int tailzerolen = 0;//小数部位转为整数后尾部补的0的个数         int index = 0;         uint32_t frontzeronum = 0;//小数部位紧跟在小数点后有效0的个数         sursavelen = declen; // 剩余应保存个数初始值为需保留小数个数         for (index = 0;; index++)         {             uint64_t div = 0;             uint64_t rem = 0;             uint64_t squ = 0;             squ = pow(10, index + 1);             div = plongnum / squ;             rem = plongnum % squ;             if (rem == 0)//余数为0，尾零个数+1             {                 tailzerolen++;             }                         if (div >= 1)//除数>= 1, 整数个数+1             {                 invallen++;             }             else             {                 invallen += 1;//加上第一位                 break;             }         }         vallen = invallen - tailzerolen;         //计算小数部位紧跟在小数点后有几个0         for (index = 0;; index++)         {             uint64_t temnum;             uint64_t div;             uint64_t squ = pow(10, invallen + index);             temnum = labs(anum) % squ;             div = labs(anum) / squ;             if (temnum == plongnum && div == intval)             {                 break;             }             else if (temnum == plongnum)             {                 frontzeronum++;             }             else             {                 frontzeronum--;                 break;             }         }         //将紧跟在小数点后的前0写入字符串         for (i = 0; i < frontzeronum; i++)         {             strcat(pstring, "0");             if (sursavelen > 0)             {                 sursavelen--;//剩余应保留个数-1             }         }         if (sursavelen > vallen)         {             sursavelen = vallen;         }                 if (sursavelen == 0)         {             uint8_t len = strlen(pstring);             if (intval == 0)             {                 for (i = 0; i < len; i++)                 {                     pstring[len - i - 1] = 0;                 }                 pstring[0] = '0';             }             else             {                 for (i = 0; i < frontzeronum + 1; i++)                 {                     pstring[len - 1 - i] = 0;                 }             }         }         else         {             sprintf(chnum, "%lld", plongnum);//将小数点后数转换为字符串             strncat(pstring, chnum, sursavelen);         }             }     return pstring; }