Linux下C获取所有可用网卡信息

在Linux下开发网络程序时，经常会遇到需要取本地网络接口名、IP、广播地址、子网掩码或者MAC地址等信息的需求，最常见的办法是配合宏SIOCGIFHWADDR、SIOCGIFADDR、SIOCGIFBRDADDR与SIOCGIFNETMASK作为参数调用函数ioctl分别获得MAC地址、IP地址、广播地址与子网掩码来实现。一次性获取此类信息的C语言代码实现如下。

 #include <stdio.h>
 #include <string.h>
 #include <net/if.h>
 #include <sys/ioctl.h>
 #include <arpa/inet.h>
 #include <errno.h>

 int getLocalInfo(void)
 {
     int fd;
     int interfaceNum = ;
     struct ifreq buf[];
     struct ifconf ifc;
     struct ifreq ifrcopy;
     char mac[] = {};
     char ip[] = {};
     char broadAddr[] = {};
     char subnetMask[] = {};

     if ((fd = socket(AF_INET, SOCK_DGRAM, )) < )
     {
         perror("socket");

         close(fd);
         return -;
     }

     ifc.ifc_len = sizeof(buf);
     ifc.ifc_buf = (caddr_t)buf;
     if (!ioctl(fd, SIOCGIFCONF, (char *)&ifc))
     {
         interfaceNum = ifc.ifc_len / sizeof(struct ifreq);
         printf("interface num = %dn", interfaceNum);
         while (interfaceNum-- > )
         {
             printf("ndevice name: %sn", buf[interfaceNum].ifr_name);

             //ignore the interface that not up or not runing
             ifrcopy = buf[interfaceNum];
             if (ioctl(fd, SIOCGIFFLAGS, &ifrcopy))
             {
                 printf("ioctl: %s [%s:%d]n", strerror(errno), __FILE__, __LINE__);

                 close(fd);
                 return -;
             }

             //get the mac of this interface
             if (!ioctl(fd, SIOCGIFHWADDR, (char *)(&buf[interfaceNum])))
             {
                 memset(mac, , sizeof(mac));
                 snprintf(mac, sizeof(mac), "%02x%02x%02x%02x%02x%02x",
                     (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[],
                     (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[],
                     (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[],

                     (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[],
                     (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[],
                     (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[]);
                 printf("device mac: %sn", mac);
             }
             else
             {
                 printf("ioctl: %s [%s:%d]n", strerror(errno), __FILE__, __LINE__);
                 close(fd);
                 return -;
             }

             //get the IP of this interface  

             if (!ioctl(fd, SIOCGIFADDR, (char *)&buf[interfaceNum]))
             {
                 snprintf(ip, sizeof(ip), "%s",
                     (char *)inet_ntoa(((struct sockaddr_in *)&(buf[interfaceNum].ifr_addr))->sin_addr));
                 printf("device ip: %sn", ip);
             }
             else
             {
                 printf("ioctl: %s [%s:%d]n", strerror(errno), __FILE__, __LINE__);
                 close(fd);
                 return -;
             }

             //get the broad address of this interface  

             if (!ioctl(fd, SIOCGIFBRDADDR, &buf[interfaceNum]))
             {
                 snprintf(broadAddr, sizeof(broadAddr), "%s",
                     (char *)inet_ntoa(((struct sockaddr_in *)&(buf[interfaceNum].ifr_broadaddr))->sin_addr));
                 printf("device broadAddr: %sn", broadAddr);
             }
             else
             {
                 printf("ioctl: %s [%s:%d]n", strerror(errno), __FILE__, __LINE__);
                 close(fd);
                 return -;
             }

             //get the subnet mask of this interface
             if (!ioctl(fd, SIOCGIFNETMASK, &buf[interfaceNum]))
             {
                 snprintf(subnetMask, sizeof(subnetMask), "%s",
                     (char *)inet_ntoa(((struct sockaddr_in *)&(buf[interfaceNum].ifr_netmask))->sin_addr));
                 printf("device subnetMask: %sn", subnetMask);
             }
             else
             {
                 printf("ioctl: %s [%s:%d]n", strerror(errno), __FILE__, __LINE__);
                 close(fd);
                 return -;

             }
         }
     }
     else
     {
         printf("ioctl: %s [%s:%d]n", strerror(errno), __FILE__, __LINE__);
         close(fd);
         return -;
     }

     close(fd);

     return ;
 }

 int main(void)
 {
     getLocalInfo();

     return ;
 }

使用ioctl函数虽然可以获取所有的信息，但是使用起来比较麻烦，如果不需要获取MAC地址，那么使用getifaddrs函数来获取更加方便与简洁。值得一提的是，在MacOS或iOS系统上（如iPhone程序开发），上述iotcl函数没法获得mac地址跟子网掩码，这个使用，使用getifaddrs函数便更有优势了。下面是使用getiaddrs函数获取网卡信息的C语言代码实现。

 #include <stdio.h>
 #include <ifaddrs.h>
 #include <arpa/inet.h>  

 int getSubnetMask()
 {
     struct sockaddr_in *sin = NULL;
     struct ifaddrs *ifa = NULL, *ifList;

     if (getifaddrs(&ifList) < )
     {
         return -;
     }

     for (ifa = ifList; ifa != NULL; ifa = ifa->ifa_next)
     {
         if(ifa->ifa_addr->sa_family == AF_INET)
         {
             printf("n>>> interfaceName: %sn", ifa->ifa_name);

             sin = (struct sockaddr_in *)ifa->ifa_addr;
             printf(">>> ipAddress: %sn", inet_ntoa(sin->sin_addr));

             sin = (struct sockaddr_in *)ifa->ifa_dstaddr;
             printf(">>> broadcast: %sn", inet_ntoa(sin->sin_addr));

             sin = (struct sockaddr_in *)ifa->ifa_netmask;
             printf(">>> subnetMask: %sn", inet_ntoa(sin->sin_addr));
         }
     }

     freeifaddrs(ifList);

     return ;
 }

 int main(void)
 {
     getSubnetMask();

     return ;
 }

ifaddrs结构体定义如下：

 struct ifaddrs
 {
     struct ifaddrs  *ifa_next;    /* Next item in list */
     char            *ifa_name;    /* Name of interface */
     unsigned int     ifa_flags;   /* Flags from SIOCGIFFLAGS */
     struct sockaddr *ifa_addr;    /* Address of interface */
     struct sockaddr *ifa_netmask; /* Netmask of interface */
     union
     {
         struct sockaddr *ifu_broadaddr; /* Broadcast address of interface */
         struct sockaddr *ifu_dstaddr; /* Point-to-point destination address */
     } ifa_ifu;
     #define              ifa_broadaddr ifa_ifu.ifu_broadaddr
     #define              ifa_dstaddr   ifa_ifu.ifu_dstaddr
     void            *ifa_data;    /* Address-specific data */
 };   

ifa_next指向链表的下一个成员；ifa_name是接口名称，以0结尾的字符串，比如eth0，lo；ifa_flags是接口的标识位（比如当IFF_BROADCAST或IFF_POINTOPOINT设置到此标识位时，影响联合体变量ifu_broadaddr存储广播地址或ifu_dstaddr记录点对点地址）；ifa_netmask存储该接口的子网掩码；结构体变量存储广播地址或点对点地址（见括弧介绍ifa_flags）；ifa_data存储了该接口协议族的特殊信息，它通常是NULL（一般不关注他）。

函数getifaddrs（int getifaddrs (struct ifaddrs **__ifap)）获取本地网络接口信息，将之存储于链表中，链表头结点指针存储于__ifap中带回，函数执行成功返回0，失败返回-1，且为errno赋值。
    很显然，函数getifaddrs用于获取本机接口信息，比如最典型的获取本机IP地址。