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 = 0;
    struct ifreq buf[16];
    struct ifconf ifc;
    struct ifreq ifrcopy;
    char mac[16] = {0};
    char ip[32] = {0};
    char broadAddr[32] = {0};
    char subnetMask[32] = {0};

    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0)
    {
        perror("socket");

        close(fd);
        return -1;
    }

    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-- > 0)
        {
            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 -1;
            }

            //get the mac of this interface  
            if (!ioctl(fd, SIOCGIFHWADDR, (char *)(&buf[interfaceNum])))
            {
                memset(mac, 0, sizeof(mac));
                snprintf(mac, sizeof(mac), "%02x%02x%02x%02x%02x%02x",
                    (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[0],
                    (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[1],
                    (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[2],

                    (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[3],
                    (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[4],
                    (unsigned char)buf[interfaceNum].ifr_hwaddr.sa_data[5]);
                printf("device mac: %sn", mac);
            }
            else
            {
                printf("ioctl: %s [%s:%d]n", strerror(errno), __FILE__, __LINE__);
                close(fd);
                return -1;
            }

            //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 -1;
            }

            //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 -1;
            }
 99 
            //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 -1;

            }
        }
    }
    else
    {
        printf("ioctl: %s [%s:%d]n", strerror(errno), __FILE__, __LINE__);
        close(fd);
        return -1;
    }
  
    close(fd);

    return 0;
}
  
int main(void)
{
    getLocalInfo();

    return 0;
}

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) < 0)
    {
        return -1;
    }

    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 0;
}
  
int main(void)
{
    getSubnetMask();

    return 0;
}

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。