通过建立好连接的ｓｏｃｋｅｔ或者ＩＰ获取对端ＭＡＣ地址

#include <stdio.h> #include <stdlib.h> #include <errno.h> #include <string.h> #include <sys/types.h> #include <netinet/in.h> #include <sys/socket.h> #include <sys/wait.h> #include <sys/ioctl.h> #include <net/if.h> #include <netinet/in.h> #include <net/if_arp.h> #include <unistd.h> #include <arpa/inet.h> #include <pthread.h> int getPeerMacbySocketFd( int sockfd, char *buf, char* localethname ) {     int ret =0;     struct arpreq arpreq;     struct sockaddr_in dstadd_in;     socklen_t  len = sizeof( struct sockaddr_in );     memset( &arpreq, 0, sizeof( struct arpreq ));     memset( &dstadd_in, 0, sizeof( struct sockaddr_in ));      if( getpeername( sockfd, (struct sockaddr*)&dstadd_in, &len ) < 0 )     {         perror( "get peer name wrong, %s/n", strerror(errno) );         return -1;     }     else     {         memcpy( ( struct sockaddr_in * )&arpreq.arp_pa, ( struct sockaddr_in * )&dstadd_in, sizeof( struct sockaddr_in ));         strcpy(arpreq.arp_dev, localethname);         arpreq.arp_pa.sa_family = AF_INET;         arpreq.arp_ha.sa_family = AF_UNSPEC;         if( ioctl( sockfd, SIOCGARP, &arpreq ) < 0 )         {             perror( "ioctl SIOCGARP wrong, %s/n", strerror(errno) );             return -1;         }         else         {             unsigned char* ptr = (unsigned char *)arpreq.arp_ha.sa_data;             sprintf(buf, "%02x:%02x:%02x:%02x:%02x:%02x", *ptr, *(ptr+1), *(ptr+2), *(ptr+3), *(ptr+4), *(ptr+5));         }      }      return ret; } int gahGetPeerMacbyIp(char *ipaddr, char* buf, char* localethname) {         int     sockfd;         unsigned char *ptr;         struct arpreq arpreq;         struct sockaddr_in *sin;         struct sockaddr_storage ss;         char addr[INET_ADDRSTRLEN+1];         memset(addr, 0, INET_ADDRSTRLEN+1);         memset(&ss, 0, sizeof(ss));         sockfd = socket(AF_INET, SOCK_DGRAM, 0);         if (sockfd == -1) {                 trace(3, "socket error");                 return -1;         }         sin = (struct sockaddr_in *) &ss;         sin->sin_family = AF_INET;         if (inet_pton(AF_INET, ipaddr, &(sin->sin_addr)) <= 0) {                 trace(3, "inet_pton error");                 return -1;         }         sin = (struct sockaddr_in *) &arpreq.arp_pa;         memcpy(sin, &ss, sizeof(struct sockaddr_in));         strcpy(arpreq.arp_dev, localethname);         arpreq.arp_ha.sa_family = AF_UNSPEC;         if (ioctl(sockfd, SIOCGARP, &arpreq) < 0) {                 trace(3, "ioctl SIOCGARP: ");                 return -1;         }         ptr = (unsigned char *)arpreq.arp_ha.sa_data;         sprintf(buf,"%02x:%02x:%02x:%02x:%02x:%02x", *ptr, *(ptr+1), *(ptr+2), *(ptr+3), *(ptr+4), *(ptr+5));         return 0; }