发送一个imcp包的方式来判断网络连通，只需要调用改进后的

bool NetIsOK()

函数即可，该函数返回true即表示网络状态良好，否则表示网络状态不连同，本程序中只发送了一个icmp包，在实际应用中可以根据需要改进为发送多个imcp包。修改之后的程序为：只需要调用函数NetIsOK()即可。源码如下所示：

--#include

---#include

--#include

--#include

--#include

--#include

--#include

---#include

--#include

---#include

---#include

--#include

---#include

--#include

---#include

----#define MAX_WAIT_TIME  1

---------#define MAX_NO_PACKETS  1

-#define ICMP_HEADSIZE 8

-#define PACKET_SIZE  4096

-#define _USE_DNS

//#define bool char

//#define false 0

//#define true 1

struct timeval tvsend,tvrecv;

struct sockaddr_in dest_addr,recv_addr;

int sockfd;

pid_t pid;

char sendpacket[PACKET_SIZE];

char recvpacket[PACKET_SIZE];

typedef enum{false=0,true=!false} bool;

//函数定义

void timeout(int signo);

unsigned short cal_chksum(unsigned short *addr,int len);

int pack(int pkt_no,char *sendpacket);

int send_packet(int pkt_no,char *sendpacket);

int recv_packet(int pkt_no,char *recvpacket);

int unpack(int cur_seq,char *buf,int len);

void tv_sub(struct timeval *out,struct timeval *in);

void _CloseSocket();

bool NetIsOk()

{

double rtt;

struct hostent *host;

struct protoent *protocol;

int i,recv_status;

// int false =0;

// int true =1;

#ifdef _USE_DNS //如果定义该宏，则可以使用域名进行判断网络连接，例如www.baidu.com

char hostname[32];

sprintf(hostname,"%s","www.baidu.com");

//sprintf(hostname,"%s","test1.wifi-times.com");

bzero(&dest_addr,sizeof(dest_addr));

dest_addr.sin_family = AF_INET;

if((host=gethostbyname(hostname))==NULL)

{

printf("[NetStatus]  error : Can't get

serverhost info!\n");

printf("%s\n",host->h_addr);

return false;

}

bcopy((char*)host->h_addr,(char*)&dest_addr.sin_addr,host->h_length);

#else //如果不使用域名，则只能用ip地址直接发送icmp包，例如谷歌的地址：8.8.8.8

dest_addr.sin_addr.s_addr = inet_addr("8.8.8.8");

#endif

if ((sockfd = socket(AF_INET,SOCK_RAW,IPPROTO_ICMP)) <

0)

{

printf("[NetStatus]  error :

socket\n");

return false;

}

int iFlag;

if(iFlag = fcntl(sockfd,F_GETFL,0)<0)

{

printf("[NetStatus]  error :

fcntl(sockfd,F_GETFL,0)");

_CloseSocket();

return false;

}

iFlag |= O_NONBLOCK;

if(iFlag = fcntl(sockfd,F_SETFL,iFlag)<0)

{

printf("[NetStatus]  error :

fcntl(sockfd,F_SETFL,iFlag )");

_CloseSocket();

return false;

}

pid=getpid();

for(i=0;i

{

if(send_packet(i,sendpacket)<0)

{

printf("[NetStatus]  error :

send_packet");

_CloseSocket();

return false;

}

if(recv_packet(i,recvpacket)>0)

{

_CloseSocket();

return true;

}

}

_CloseSocket();

return false;

}

int send_packet(int pkt_no,char *sendpacket)

{

int packetsize;

packetsize=pack(pkt_no,sendpacket);

gettimeofday(&tvsend,NULL);

if(sendto(sockfd,sendpacket,packetsize,0,(struct sockaddr

*)&dest_addr,sizeof(dest_addr) )<0)

{

printf("[NetStatus]  error : sendto

error");

return -1;

}

return 1;

}

int pack(int pkt_no,char*sendpacket)

{

int i,packsize;

struct icmp *icmp;

struct timeval *tval;

icmp=(struct icmp*)sendpacket;

icmp->icmp_type=ICMP_ECHO;  //设置类型为ICMP请求报文

icmp->icmp_code=0;

icmp->icmp_cksum=0;

icmp->icmp_seq=pkt_no;

icmp->icmp_id=pid; //设置当前进程ID为ICMP标示符

packsize=ICMP_HEADSIZE+sizeof(struct timeval);

tval= (struct timeval *)icmp->icmp_data;

gettimeofday(tval,NULL);

icmp->icmp_cksum=cal_chksum( (unsigned short

*)icmp,packsize);

return packsize;

}

unsigned short cal_chksum(unsigned short *addr,int len)

{

int nleft=len;

int sum=0;

unsigned short *w=addr;

unsigned short answer=0;

while(nleft>1) //把ICMP报头二进制数据以2字节为单位累加起来

{

sum+=*w++;

nleft-=2;

}

if( nleft==1)

//若ICMP报头为奇数个字节,会剩下最后一字节.把最后一个字节视为一个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

{

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

sum+=answer;

}

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

sum+=(sum>>16);

answer=~sum;

return answer;

}

int recv_packet(int pkt_no,char *recvpacket)

{

int n,fromlen;

fd_set rfds;

FD_ZERO(&rfds);

FD_SET(sockfd,&rfds);

signal(SIGALRM,timeout);

fromlen=sizeof(recv_addr);

alarm(MAX_WAIT_TIME);

while(1)

{

select(sockfd+1, &rfds, NULL, NULL, NULL);

if (FD_ISSET(sockfd,&rfds))

{

if( (n=recvfrom(sockfd,recvpacket,PACKET_SIZE,0,(struct

sockaddr *)&recv_addr,&fromlen)) <0)

{

if(errno==EINTR)

return -1;

perror("recvfrom error");

return -2;

}

}

gettimeofday(&tvrecv,NULL);

if(unpack(pkt_no,recvpacket,n)==-1)

continue;

return 1;

}

}

int unpack(int cur_seq,char *buf,int len)

{

int iphdrlen;

struct ip *ip;

struct icmp *icmp;

ip=(struct ip *)buf;

iphdrlen=ip->ip_hl<<2; //求ip报头长度,即ip报头的长度标志乘4

icmp=(struct icmp *)(buf+iphdrlen); //越过ip报头,指向ICMP报头

len-=iphdrlen; //ICMP报头及ICMP数据报的总长度

if( len<8)

return -1;

if( (icmp->icmp_type==ICMP_ECHOREPLY) &&

(icmp->icmp_id==pid) &&

(icmp->icmp_seq==cur_seq))

return 0;

else return -1;

}

void timeout(int signo)

{

printf("Request Timed Out\n");

}

void tv_sub(struct timeval *out,struct timeval *in)

{

if( (out->tv_usec-=in->tv_usec)<0)

{

--out->tv_sec;

out->tv_usec+=1000000;

}

out->tv_sec-=in->tv_sec;

}

void _CloseSocket()

{

close(sockfd);

sockfd = 0;

}

int main()

{

int flag=-1;

if(NetIsOk())

printf("wwww=\n");

}