实现ping命令的代码

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#define    PACKET_SIZE 4096            /*  */
#define MAX_WAIT_TIME 5
#define MAX_NO_PACKETS 3
   
char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];
int sockfd,datalen=56;
int nsend=0,nreceived=0;
struct sockaddr_in dest_addr;
pid_t pid;
struct sockaddr_in from;
struct timeval tvrecv;
void statistics(int signo);
unsigned short cal_chksum(unsigned short *addr,int len);
int pack(int pack_no);
void send_packet(void);
void recv_packet(void);
int unpack(char* buf,int len);
void tv_sub(struct timeval *out,struct timeval* in);
   
void statistics(int signo)
{
   printf("\n-----------------PING statistics----------------\n");
   printf("%d packet transmitted,%d received,%%%d lost \n",nsend,nreceived,(nsend-nreceived)/nsend*100);
   close(sockfd);
   exit(1);
}
/*校验和算法*/
unsigned short cal_chksum(unsigned short *addr,int len)
{
   int nleft=len;
   int sum=0;
   unsigned short *w=addr;
   unsigned short answer=0;
   /*把ICMP报头二进制数据以2字节为单位累加起来*/
   while(nleft>1)
   {
       sum+=*w++;
       nleft-=2;
   }
   /*若ICMP报头为奇数个字节，会剩下最后一个字节。把最后一个字节视为2字节数据的高字节，这个2字节数据的低字节为0，继续累加*/
   if(nleft==1)
   {
       *(unsigned char *)(&answer)=*(unsigned char *)w;
       sum+=answer;
   }
   sum=(sum>>16)+(sum&0xffff);
   sum+=(sum>>16);
   answer=~sum;
   return answer;
}
/*设置ICMP报头*/
int pack(int pack_no)
{
   int packsize;
   struct icmp *icmpp;
   struct timeval *tval;
   icmpp=(struct icmp *)sendpacket;
   icmpp->icmp_type=ICMP_ECHO;
   icmpp->icmp_code=0;
   icmpp->icmp_cksum=0;
   icmpp->icmp_seq=pack_no;
   icmpp->icmp_id=pid;
   packsize=8+datalen;
   tval=(struct timeval *)icmpp->icmp_data;
   gettimeofday(tval,NULL);/*记录发送时间*/
   icmpp->icmp_cksum=cal_chksum((unsigned short*)icmpp,packsize);/*校验算法*/
   return packsize;
}
/*发送3个ICMP报文*/
void send_packet()
{
   int packetsize;
   while(nsendip_hl)*4;/*求IP报头长度，即IP报头的长度标志乘4*/
   icmpp=(struct icmp*)(buf+iphdrlen);/*超过IP报头，指向ICMP报头*/
   len-=iphdrlen;/*ICMP报头及ICMP数据报的总长度*/
   if(lenicmp_type==ICMP_ECHOREPLY)&&(icmpp->icmp_id==pid))
   {
       tvsend=(struct timeval *)icmpp->icmp_data;
       tv_sub(&tvrecv,tvsend); /*接收和发送的时间差*/
       rtt=tvrecv.tv_sec*1000+tvrecv.tv_usec/1000;/*以毫秒为单位计算rtt*/
       /*显示相关信息*/
       printf("%d byte from %s:icmp_seq=%u ttl=%d rtt=%d  ms\n",
               len,inet_ntoa(from.sin_addr),icmpp->icmp_seq,ipp->ip_ttl,rtt);
   }
   else
       return -1;
}
void tv_sub(struct timeval *out,struct timeval *in)
{
   if((out->tv_usec-=in->tv_usec)tv_sec-=1;
       out->tv_usec+=1000000;
   }
   out->tv_sec-=in->tv_sec;
}
int main(int argc,char **argv)
{
   struct hostent *host;
   struct protoent *protocol;
   int size=50*1024;
   if(argcp_proto))h_addr);
   pid=getpid();
   printf("PING %s(%s): %d bytes data in ICMP packets.\n",argv[1],inet_ntoa(dest_addr.sin_addr),datalen);
   send_packet();/*发送所有ICMP报文*/
   recv_packet();/*接收所有ICMP报文*/
   statistics(SIGALRM);/*进行统计*/
   
   return 0;
}
本文出自 “好好活着” 博客，请务必保留此出处http://wolfword.blog.51cto.com/4892126/1225685