linux下运行Ｃ程序的错误信息为 segmentation fault
我在运行用Ｃ写的ping代码出现segmentation fault
原代码是
#include <stdio.h>
#include <stdlib.h>
#include <memory.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 <netinet/ip_icmp.h>
#include <netdb.h>
#include <setjmp.h>
#include <errno.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 packets 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*/
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 i,packsize;
struct icmp *icmp;
struct timeval *tval;
icmp=(struct icmp*)sendpacket;
icmp-> icmp_type=ICMP_ECHO;
icmp-> icmp_code=0;
icmp-> icmp_cksum=0;
icmp-> icmp_seq=pack_no;
icmp-> icmp_id=pid;
packsize=8+datalen;
tval= (struct timeval *)icmp-> icmp_data;
gettimeofday(tval,NULL); /*记录发送时间*/
icmp-> icmp_cksum=cal_chksum( (unsigned short *)icmp,packsize); /*校验算法*/
return packsize;
}
/*发送三个ICMP报文*/
void send_packet()
{ int packetsize;
while( nsend <MAX_NO_PACKETS)
{ nsend++;
packetsize=pack(nsend); /*设置ICMP报头*/
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*/
}
}
/*接收所有ICMP报文*/
void recv_packet()
{ int n,fromlen;
extern int errno;
signal(SIGALRM,statistics);
fromlen=sizeof(from);
while( nreceived <nsend)
{ alarm(MAX_WAIT_TIME);
if( (n=recvfrom(sockfd,recvpacket,sizeof(recvpacket),0,
(struct sockaddr *)&from,&fromlen)) <0)
{ if(errno==EINTR)continue;
perror( "recvfrom error ");
continue;
}
gettimeofday(&tvrecv,NULL); /*记录接收时间*/
if(unpack(recvpacket,n)==-1)continue;
nreceived++;
}
}
/*剥去ICMP报头*/
int unpack(char *buf,int len)
{ int i,iphdrlen;
struct ip *ip;
struct icmp *icmp;
struct timeval *tvsend;
double rtt;
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) /*小于ICMP报头长度则不合理*/
{ printf( "ICMP packets\ 's length is less than 8\n ");
return -1;
}
/*确保所接收的是我所发的的ICMP的回应*/
if( (icmp-> icmp_type==ICMP_ECHOREPLY) && (icmp-> icmp_id==pid) )
{ tvsend=(struct timeval *)icmp-> 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=%.3f ms\n ",
len,
inet_ntoa(from.sin_addr),
icmp-> icmp_seq,
ip-> ip_ttl,
rtt);
}
else return -1;
}
main(int argc,char *argv[])
{ struct hostent *host;
struct protoent *protocol;
unsigned long inaddr=0l;
int waittime=MAX_WAIT_TIME;
int size=50*1024;
if(argc <2)
{ printf( "usage:%s hostname/IP address\n ",argv[0]);
exit(1);
}
if( (protocol=getprotobyname( "icmp ") )==NULL)
{ perror( "getprotobyname ");
exit(1);
}
/*生成使用ICMP的原始套接字,这种套接字只有root才能生成*/
if( (sockfd=socket(AF_INET,SOCK_RAW,protocol-> p_proto) ) <0)
{ perror( "socket error ");
exit(1);
}
/* 回收root权限,设置当前用户权限*/
setuid(getuid());
/*扩大套接字接收缓冲区到50K这样做主要为了减小接收缓冲区溢出的
的可能性,若无意中ping一个广播地址或多播地址,将会引来大量应答*/
setsockopt(sockfd,SOL_SOCKET,SO_RCVBUF,&size,sizeof(size) );
bzero(&dest_addr,sizeof(dest_addr));
dest_addr.sin_family=AF_INET;
/*判断是主机名还是ip地址*/
if( inaddr=inet_addr(argv[1])==INADDR_NONE)
{ if((host=gethostbyname(argv[1]) )==NULL) /*是主机名*/
{ perror( "gethostbyname error ");
exit(1);
}
memcpy( (char *)&dest_addr.sin_addr,host-> h_addr,host-> h_length);
}
else /*是ip地址*/
memcpy( (char *)&dest_addr,(char *)&inaddr,host-> h_length);
/*获取main的进程id,用于设置ICMP的标志符*/
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;
}
/*两个timeval结构相减*/
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;
}
有知道的帮帮忙好吗 非常非常感谢！
[解决办法]
if( inaddr=inet_addr(argv[1])==INADDR_NONE)
改为
if( (inaddr = inet_addr(argv[1])) == INADDR_NONE)
最好改为
if( INADDR_NONE == (inaddr = inet_addr(argv[1])) )
[解决办法]
用GDB很容易发现core dump 发生在
memcpy( (char *)&dest_addr,(char *)&inaddr,host-> h_length);
改为：
memcpy( (char *)&dest_addr,(char *)&inaddr,sizeof(dest_addr));
后没有core dump了，可是如果参数是ip地址，是没有返回包的，
从输出的信息可以发现，你取到的ip是错的，
改为
memcpy( (char *)&dest_addr.sin_addr,(char *)&inaddr,sizeof(dest_addr
));
就可以了！
