指针的一种用法（优化代码）

 函数名 ：unsigned char CAN_Send_dat(CAN_DAT *can_tmp,unsigned char pir)
 功能 　：can发送
 参数 　：*can_tmp 数据包 pir: 优先级 0~3
 返回 　：1->缓冲池满需要等待下次装入发送缓冲池 0->成功放入缓冲池
************************************************************************/
unsigned char CAN_Send_dat(CAN_DAT *can_tmp,unsigned char pir)
{
 unsigned char n,flag;
 unsigned char temp;
 unsigned char *P_addr,*P_addr_temp;
 flag = 0;
 if((TXB0CON&0x08)==0)
  {
   P_addr = (unsigned char*)(&TXB0CON);
   flag = 1;
  }
 if((TXB1CON&0x08)==0)
  {
   P_addr = (unsigned char*)(&TXB1CON);
   flag = 1;
  }
 if((TXB2CON&0x08)==0)
  {
   P_addr = (unsigned char*)(&TXB2CON);
   flag = 1;
  }
if(flag==1)
  {
       P_addr_temp = P_addr;
      *P_addr = pir;
       P_addr++;
      if(can_tmp->IDR_RTR&0x02)//扩展标识符
      {
       *P_addr = ((can_tmp->ID[2]>>5)|(can_tmp->ID[3]<<3));
       temp = can_tmp->ID[2]&0x03;
       temp|=((can_tmp->ID[2]&0x1C)<<3);
       temp|= 0x08;
       P_addr++;
       *P_addr = temp;
       P_addr++;
       *P_addr = can_tmp->ID[1];
       P_addr++;
       *P_addr = can_tmp->ID[0];
       P_addr++;
      }
     else
    {
        *P_addr = ((can_tmp->ID[1]<<5)|(can_tmp->ID[0]>>3));;
         P_addr++;
        *P_addr = (can_tmp->ID[0]<<5);
         P_addr+=3;
   }
        *P_addr = can_tmp->length;
        P_addr++;
       for(n=0;nlength;n++)
        {
        *P_addr =can_tmp->DATA[n];
        P_addr++;
       }
       *P_addr_temp |= 0x08;
      return 0;
  }
  return 1;
}
/************************************************************************
 函数名 ：unsigned char CAN_Send_dat(CAN_DAT *can_tmp,unsigned char pir)
 功能 　：can发送
 参数 　：*can_tmp 数据包 pir: 优先级 0~3
 返回 　：1->缓冲池满需要等待下次装入发送缓冲池 0->成功放入缓冲池
************************************************************************/
unsigned char CAN_Send_dat(CAN_DAT *can_tmp,unsigned char pir)
{
 unsigned char n;
 unsigned char temp;
 unsigned char *P_addr;
if((TXB0CON&0x08)==0)
   {
   // TXB0CON&=0xfc;
   //bit3=0标准标识符,bit3=1扩展标识符,bit7-5:标准标识符2-0位,bit7-5 扩展ID[16-17]
    TXB0CON = pir;//|= pir;           //设置TXB0为最高优先级3
   if(can_tmp->IDR_RTR&0x02)//扩展标识符
   {
 TXB0EIDL  = can_tmp->ID[0];//扩展ID[0-7]
 TXB0EIDH  = can_tmp->ID[1];//扩展ID[8-15]
 TXB0SIDL  = can_tmp->ID[2]&0x03;//扩展ID[16-17]
    temp= ((can_tmp->ID[2]&0x1C)<<3);
    TXB0SIDL |= temp;//标准[0-3]
    TXB0SIDL |= 0x08;
 TXB0SIDH=((can_tmp->ID[2]>>5)|(can_tmp->ID[3]<<3));//标准标识符的10-3位
   }
   else
   {
    TXB0SIDL = (can_tmp->ID[0]<<5);//标准[0-3]
    TXB0SIDH = ((can_tmp->ID[1]<<5)|(can_tmp->ID[0]>>3));
   }
//if(can_tmp->IDR_RTR&0x01)can_tmp->length|=0x40;
 TXB0DLC=can_tmp->length;
    P_addr = &TXB0D0;
    for(n=0;nlength;n++)
    {
     *P_addr =can_tmp->DATA[n];
      P_addr++;
    }
    TXB0CON=TXB0CON|0x08; /* bit3(TXREQ)=1请求发送 */
    return 0;
  }
  if((TXB1CON&0x08)==0)
   {
   // TXB1CON&=0xfc;
    TXB1CON = pir;//|= pir;
   if(can_tmp->IDR_RTR&0x02)//扩展标识符
   {
 TXB1EIDL  = can_tmp->ID[0];//扩展ID[0-7]
 TXB1EIDH  = can_tmp->ID[1];//扩展ID[8-15]
 TXB1SIDL  = can_tmp->ID[2]&0x03;//扩展ID[16-17]
    temp= ((can_tmp->ID[2]&0x1C)<<3);
    TXB1SIDL |= temp;//标准[0-3]
    TXB1SIDL |= 0x08;
 TXB1SIDH=((can_tmp->ID[2]>>5)|(can_tmp->ID[3]<<3));//标准标识符的10-3位
   }
   else
   {
    TXB1SIDL = (can_tmp->ID[0]<<5);//标准[0-3]
    TXB1SIDH = ((can_tmp->ID[1]<<5)|(can_tmp->ID[0]>>3));
   }
  //if(can_tmp->IDR_RTR&0x01)can_tmp->length|=0x40;
 TXB1DLC=can_tmp->length;
 
    P_addr = &TXB1D0;
    for(n=0;nlength;n++)
    {
     *P_addr =can_tmp->DATA[n];
      P_addr++;
    }
    TXB1CON=TXB1CON|0x08; 
return 0;
  }
if((TXB2CON&0x08)==0)
  {
    //TXB2CON&=0xfc;
    TXB2CON = pir;
   if(can_tmp->IDR_RTR&0x02)//扩展标识符
   {
 TXB2EIDL  = can_tmp->ID[0];//扩展ID[0-7]
 TXB2EIDH  = can_tmp->ID[1];//扩展ID[8-15]
 TXB2SIDL  = can_tmp->ID[2]&0x03;//扩展ID[16-17]
    temp= ((can_tmp->ID[2]&0x1C)<<3);
    TXB2SIDL |= temp;//标准[0-3]
    TXB2SIDL |= 0x08;
 TXB2SIDH=((can_tmp->ID[2]>>5)|(can_tmp->ID[3]<<3));//标准标识符的10-3位
   }
   else
   {
    TXB2SIDL = (can_tmp->ID[0]<<5);//标准[0-3]
    TXB2SIDH = (can_tmp->ID[1]<<5|(can_tmp->ID[0]>>3));
   }
// if(can_tmp->IDR_RTR&0x01)can_tmp->length|=0x40;
 TXB2DLC=can_tmp->length;
  
    P_addr = &TXB2D0;
    for(n=0;nlength;n++)
    {
     *P_addr =can_tmp->DATA[n];
      P_addr++;
    }
    TXB2CON=TXB2CON|0x08; 
return 0;
  }
return 1;
}