环形buffer缓冲区

 #include <stdio.h>
 #include <string.h>
 #include <malloc.h>

 struct CircleBuf
 {
     char *pFirst;//指向循环表开始的位置
     char *pLast;//指向循环表结尾的位置
     char *plSave;//指向最后一个存数据的后一位，没有数据为NULL，或与pfsave相等
     char *pfSave;//指向第一个存数据的位置，没有数据为NULL，或与plsave相等
     int iSize;//循环表的大小
     int iDataNum;//存数据的大小
 };

 int InitCircleBuf(struct CircleBuf *buf, const int bufSize)
 //初始化缓冲区。buf为目标缓冲区。字节数为bufSize,能存储bufSize 个字符
 //操作成功返回1，操作失败返回0.
 {
     buf->pFirst = (char*)malloc((bufSize + )*(sizeof(char)));//初始化CiecleLink
     if(NULL == buf->pFirst)
     {
         printf("\nMemory allocation failure !\n");
         return ;
     }
     buf->iSize = bufSize;
     buf->iDataNum = ;
     buf->pfSave = NULL;
     buf->plSave = NULL;
     buf->pLast = buf->pFirst + buf->iSize;
     return ;
 }

 void DestroyCircleBuf(struct CircleBuf *buf)
 //销毁环形缓冲区
 {
     free(buf->pFirst);
     buf->iDataNum = ;
     buf->iSize = ;
     buf->pFirst = NULL;
     buf->pLast = NULL;
     buf->plSave = NULL;
     buf->pfSave = NULL;
 }

 void ClearCircleBuf(struct CircleBuf *buf)
 //清空环形缓冲区
 {
     buf->plSave = NULL;
     buf->pfSave = NULL;
     buf->iDataNum = ;
 }

 int InCircleBuf(struct CircleBuf *buf, char *str, int length)
 //向循环表存入数据。buf为目标循环表，str为源字符串地址，存入的字节数为length
 //操作成功返回 1， 操作失败返回 0
 {
     int i;
     int j;
     int len;
     int lengthtem;
     len = strlen(str);
     if(len < length)
     {
         printf("the length is longer then the size of str !\n");
         return ;

     }

     if((NULL == buf->pfSave) &&(NULL == buf->plSave))//CircleBuf为空时
     {
         if(length > (buf->iSize - ))
         {
             printf("length is longer then the size of Circlebuf !\n");
             return ;
         }
         else
         {

             strncpy(buf->pFirst, str, length);
             buf->pfSave = buf->pFirst;
             buf->plSave = buf->pfSave + length;
             buf->iDataNum += length;

         }
     }
     else if(buf->pfSave <= buf->plSave)//pfsave小于或等于plsave，存数据没有超过结尾处
     {

         if(length < (buf->pLast - buf->plSave + ))//存数据的length没有达到CircleBuf结尾
         {

             strncpy(buf->plSave, str, length);
             buf->iDataNum += length;
             buf->plSave += length;
         }
         else if(length == (buf->pLast - buf->plSave + ))//存数据的length刚好到CircleBuf结尾处
         {

             if(buf->pfSave > buf->pFirst)
             {
                 strncpy(buf->plSave, str, length);
                 buf->iDataNum += length;
                 buf->plSave = buf->pFirst;
             }
             else
             {
                 printf("the length is longer then the unused space !\n");
                 return ;
             }
         }
         else   //存数据的length长度超过CircleBuf结尾
         {

             if(length > ((buf->pLast - buf->plSave)+(buf->pfSave - buf->pFirst)))
                 //存数据的length大于剩余空间大小
             {
                 printf("length is too long then the unused space!\n");
                 return ;
             }
             else  //存数据的length小于剩余空间大小，将length长度数据分两次存
             {

                 lengthtem = length - (buf->pLast - buf->plSave + );
                 for(i=; i<(buf->pLast - buf->plSave + ); i++)
                 {
                     *(buf->plSave + i) = str[i];

                 }
                 buf->plSave = buf->pFirst;

                 for(j=; j<lengthtem; j++)
                 {
                     *(buf->plSave + j) = str[i + j];

                 }

                 buf->plSave += j;
                 buf->iDataNum += length;

             }
         }
     }
     else if(buf->pfSave > buf->plSave)//pfsave大于plsave，存数据超过结尾处，至少绕了一圈
     {
         if(length > (buf->pfSave - buf->plSave))//存数据的length大于剩余空间大小
         {
             printf("length is too long then the unsued space!\n");
             return ;
         }
         else
         {
             strncpy(buf->plSave, str, length);
             buf->iDataNum += length;
             buf->plSave += length;
         }
     }
     return ;
 }

 int OutCircleBuf(char *str, struct CircleBuf *buf, int length)
 //从循环表中取数据。 str为目标字符串地址， buf为源循环表， 取出的字节数为length
 //操作成功返回 1， 操作失败返回 0
 {
     int i;
     int j;
     int lengthtem;

     if((NULL == buf->pfSave) &&(NULL == buf->plSave))//CircleBuf为空
     {
         printf("the Circlebuf is empty !\n");
         return ;
     }

     if(buf->pfSave < buf->plSave)//pfsave小于plsave，存的数据没有超过结尾
     {
         if((buf->pfSave + length) > buf->plSave)
         {
             printf("length is longer then the used of Circlebuf !\n");
             return ;
         }
         else
         {
             strncpy(str, buf->pfSave, length);
             buf->pfSave += length;
             buf->iDataNum -= length;
         }
     }
     else if(buf->pfSave == buf->plSave)//pfsave等于plsave，CircleBuf为空
     {
         printf("there is no data in Circlebuf !\n");
         return ;
     }
     else if(buf->pfSave > buf->plSave)//pfsave大于plsave，存的数据超过结尾，至少绕了一圈
     {

         if(length < (buf->pLast - buf->pfSave + ))//取数据的length没到结尾
         {
             strncpy(str, buf->pfSave, length);
             buf->pfSave += length;
             buf->iDataNum -= length;
         }
         else if(length == (buf->pLast - buf->pfSave + ))//取数据的length刚好达到结尾处
         {
             strncpy(str, buf->pfSave, length);
             buf->pfSave = buf->pFirst;
             buf->iDataNum -= length;
         }
         else //取数据的length超过结尾
         {

             if((length - (buf->pLast - buf->pfSave + )) > (buf->plSave - buf->pFirst))
             //取数据的length大于剩余数据的大小
             {
                 printf("%d\n",(buf->plSave - buf->pFirst));
                 printf("the used data is shorter then length !\n");
                 return ;
             }
             else //取数据的length小于剩余数据的大小，将数据分开两次取出来
             {
                 lengthtem = length - (buf->pLast - buf->pfSave + );
                 for(i=; i<(buf->pLast - buf->pfSave + ); i++)
                 {
                     str[i] = *(buf->pfSave +i);
                 }
                 buf->pfSave = buf->pFirst;
                 for(j=; j<lengthtem; j++)
                 {
                     str[i + j] = *(buf->pfSave + j);
                 }
                 buf->pfSave += j;
                 buf->iDataNum -= length;
             }
         }
     }
     str[length] = '\0';
     return ;
 }

 int CalDataNumCB(struct CircleBuf *buf)
 //计算循环表的数据个数。buf为目标循环表
 //返回已存放数据的字节数
 {
     return buf->iDataNum;
 }

 int CalSpaceNumCB(struct CircleBuf *buf)
 //计算循环表的剩余空间大小。 buf为目标循环表
 //返回剩余空间字节数
 {
     return (buf->iSize - buf->iDataNum);
 }

 int OutCBtoFile(char *filename, struct CircleBuf *buf)
 //将循环表中所有的数据都存到所给的文件中，filename为目标文件的路径及名称，buf为源循环表。
 //操作成功返回 1， 操作失败返回 0
 {
     FILE *fp;
     int i;
     int length;
     char ch[];
     if(NULL == (fp = fopen(filename, "wt+")))//判断文件是否打开
     {
         printf("can't open %s !\n", filename);
         return ;
     }
     length = CalDataNumCB(buf);

     for(i=; i<length; i++)        //将全部数据读入文件中
     {
         OutCircleBuf(ch, buf, );
         printf("%d   %c   \n", strlen(ch), ch[]);
         fwrite(ch, , , fp);

     }

     fclose(fp);
     return ;
 }

 int InCBfromFile(struct CircleBuf *buf, char *filename)
 //将文件中的数据读到循环链表中，clink为目标链表，filename为源文件的路径及名称。
 //操作失败返回0， 文件数据全部存储完毕返回1， clink空间不足，只存入部分数据返回-1
 {
     FILE *fp;
     int length;
     char ch;

     if(NULL == (fp = fopen(filename, "rt+")))// 文件打开失败
     {
         printf("can't open %s !\n", filename);
         return ;
     }
     else
     {
         length = CalSpaceNumCB(buf);
         if( == length)                     //循环表数据已满
         {
             printf("CircleLink is full!\n");
             return ;
         }
         else
         {
             while()
             {
                 if( == length )           //循环表空间已满，还有部分数据未读入
                 {
                     printf("CircleBuf is full, some data still in file %s !\n", filename);
                     return -;
                 }
                 else
                 {
                     ch = fgetc(fp);
                     if(ch == EOF)
                     {
                         printf("file %s is over, data are in Circlebuf now!\n", filename);
                                           //文件数据全部读完，并存入表中
                         return ;
                     }
                     else
                     {

                         InCircleBuf(buf, &ch, );
                         length--;
                     }

                 }

             }

         }
     }
     return ;
 }