在下边的代码中我知道它们分别代表IP数据包的什么字段,但是它们的具体格式我还是不太清楚。本人菜鸟,求大神指教啊。
1.m_nVersion=*pos/16;
m_nHeaderLength = *pos%16; //这里的“/”和“%”是什么含义?
2.m_nPrecedence=(*pos & 16)*4+(*pos & 8)*2+(*pos & 4);
//这里的“*4”是指指针向有移动2位吗?
CIPPacket::CIPPacket(const unsigned char buf,int buflen)
{
unsigned char *pos;
pos=(unsigned char *)buf;
m_nVersion=*pos/16;
m_nHeaderLength = *pos%16;
pos++;
m_nServiceType=*pos;
m_nPrecedence=(*pos & 16)*4+(*pos & 8)*2+(*pos & 4);
if(*pos & 16)
m_bDelay = true;
else
m_bDelay = false;
if(*pos & 8)
m_bThroughtPut = true;
else
m_bThroughtPut = false;
if(*pos & 4)
m_bReliability = true;
else
m_bReliability = false;
pos++;
m_uTotalLength=(*pos)*256+((pos+1));
pos+=2;
m_nIdentification=(*pos)*256+(*(pos+1));
pos+=2;
if(*pos & 64)
m_bDF=true;
else
m_bDF=false;
if(*pos & 32)
m_bMF=true;
else
m_bMF=false;
m_nFragOffSet=(*pos%32)*256+(*(pos+1));
pos+=2;
m_nTTL = pos;
pos++;
m_nProtocol = *pos;
pos++;
m_nCheckSum = (*pos)*256+((pos+1));
pos+=2;
m_lSrcIP = (*pos)*0x1000000+(*(pos+1))*0x10000+(*(pos+2))*0x100+(*(pos+3));
pos+=4;
m_lDestIP = (*pos)*0x1000000+(*(pos+1))*0x10000+(*(pos+2))*0x100+(*(pos+3));
if(m_nHeaderLength > 5)
{
pos += 4;
m_nOptLength=(m_nHeaderLength-5)*4;
m_pOptions=new unsigned char[m_nOptLength];
memcpy(m_pOptions,buf+20,m_nOptLength);
}
else
{
m_nOptLength = 0;
m_pOptions = NULL;
}
pos=(unsigned char *)(buf+m_nHeaderLength*4);
m_nDataLength = m_uTotalLength-m_nHeaderLength*4;
if(m_nDataLength > 0)
{
m_pData=new unsigned char[m_nDataLength];
memcpy(m_pData,buf+m_nHeaderLength*4,m_nDataLength);
}
else
m_pData = NULL;