实现ping呼吁的代码

#include    <stdio.h>

#include    <sys/time.h>

#include    <signal.h>

#include    <arpa/inet.h>

#include    <sys/types.h>

#include    <sys/socket.h>

#include    <unistd.h>

#include    <netinet/in.h>

#include    <netinet/ip.h>

#include    <netdb.h>

#include    <setjmp.h>

#include    <errno.h>

#include    <netinet/ip_icmp.h>

#include    <string.h>

#include    <stdlib.h>

#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字节为单元累加起来*/

   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，继承累加*/

   if(nleft==1)

   {

       *(unsigned char *)(&answer)=*(unsigned char *)w;

       sum+=answer;

   }

   sum=(sum>>16)+(sum&0xffff);

   sum+=(sum>>16);

   answer=~sum;

   return answer;

}

/*配置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(nsend<MAX_NO_PACKETS)

   {

       nsend++;

       packetsize=pack(nsend);/*配置ICMP报文*/

       if(sendto(sockfd,sendpacket,packetsize,0,(struct sockaddr *)&dest_addr,sizeof(dest_addr))<0)

       {

           perror("sendto error");

           continue;

       }

       sleep(1);/*每隔一秒发送一个ICMP报文*/

   }

}

/*吸收所有ICMP报文*/

void recv_packet()

{

   int n,fromlen;

   extern int errno;

  /*