在Linux下開發網絡程序時,經常會遇到需要取本地網絡接口名、IP、廣播地址、子網掩碼或者MAC地址等信息的需求,最常見的辦法是配合宏SIOCGIFHWADDR、SIOCGIFADDR、SIOCGIFBRDADDR與SIOCGIFNETMASK作爲參數調用函數ioctl分別獲得MAC地址、IP地址、廣播地址與子網掩碼來實現。一次性獲取此類信息的C語言代碼實現如下。
#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;
}
//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函數雖然可以獲取所有的信息,但是使用起來比較麻煩,如果不需要獲取MAC地址,那麼使用getifaddrs函數來獲取更加方便與簡潔。值得一提的是,在MacOS或iOS系統上(如iPhone程序開發),上述iotcl函數沒法獲得mac地址跟子網掩碼,這個使用,使用getifaddrs函數便更有優勢了。下面是使用getiaddrs函數獲取網卡信息的C語言代碼實現。
#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結構體定義如下:
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指向鏈表的下一個成員;ifa_name是接口名稱,以0結尾的字符串,比如eth0,lo;ifa_flags是接口的標識位(比如當IFF_BROADCAST或IFF_POINTOPOINT設置到此標識位時,影響聯合體變量ifu_broadaddr存儲廣播地址或ifu_dstaddr記錄點對點地址);ifa_netmask存儲該接口的子網掩碼;結構體變量存儲廣播地址或點對點地址(見括弧介紹ifa_flags);ifa_data存儲了該接口協議族的特殊信息,它通常是NULL(一般不關注他)。
函數getifaddrs(int getifaddrs (struct ifaddrs **__ifap))獲取本地網絡接口信息,將之存儲於鏈表中,鏈表頭結點指針存儲於__ifap中帶回,函數執行成功返回0,失敗返回-1,且爲errno賦值。
很顯然,函數getifaddrs用於獲取本機接口信息,比如最典型的獲取本機IP地址。