各位大侠：帮忙看看这段代码什么意思？

Question

void CGps::AddChecksum(LPSTR cmd,LPSTR chksum)
{
int nIndex;
int nLength;
unsigned char cChkSum;
unsigned char str[4];
    if(cmd==NULL||chksum==NULL) return;
nLength=strlen(cmd);
if(nLength<1) return;
memset(str,0,sizeof(str));
    cChkSum=0;
nIndex=1;
while(nIndex<nLength)
{ cChkSum=cChkSum^cmd[nIndex];
  nIndex++;}
    sprintf((char*)str,"*%02X",cChkSum); 
strcpy(chksum,cmd);
chksum[nLength]=str[0];
chksum[nLength+1]=str[1];
chksum[nLength+2]=str[2];
}

Answer 1

就是在命令行cmd后面加上cChkSum,cChkSum是cmd中从第1位到第nLength位异或的结果，str存放的是cChkSum的字符形式