linux 下获取当前网络连接状态的两种方法

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 #include <linux/sockios.h>
 #include <sys/socket.h>
 #include <sys/ioctl.h>
 #include <linux/if.h>
 #include <string.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>

 #define ETHTOOL_GLINK        0x0000000a /* Get link status (ethtool_value) */

 typedef enum { IFSTATUS_UP, IFSTATUS_DOWN, IFSTATUS_ERR } interface_status_t;

 typedef signed int u32;

 /* for passing single values */
 struct ethtool_value
 {
     u32    cmd;
     u32    data;
 };

 interface_status_t interface_detect_beat_ethtool(int fd, char *iface)
 {
     struct ifreq ifr;
     struct ethtool_value edata;

     memset(&ifr, 0, sizeof(ifr));
     strncpy(ifr.ifr_name, iface, sizeof(ifr.ifr_name)-1);

     edata.cmd = ETHTOOL_GLINK;
     ifr.ifr_data = (caddr_t) &edata;

     if (ioctl(fd, SIOCETHTOOL, &ifr) == -1)
     {
         perror("ETHTOOL_GLINK failed ");
         return IFSTATUS_ERR;
     }

     return edata.data ? IFSTATUS_UP : IFSTATUS_DOWN;
 }

 int main (int argc, char *argv[])
 {
     FILE *fp;
     interface_status_t status;
     char buf[512] = {'\0'};
     char hw_name[10] = {'\0'};
     char *token = NULL;

     /* 获取网卡名称 */
     if ((fp = fopen("/proc/net/dev", "r")) != NULL)
     {
         while (fgets(buf, sizeof(buf), fp) != NULL)
         {
             if(strstr(buf, "eth") != NULL)
             {
                 token = strtok(buf, ":");
                 while (*token == ' ') ++token;
                 strncpy(hw_name, token, strlen(token));
             }
         }
     }
     fclose(fp);
 //方法一：查看一个文件文件，相对来说比较简单
 #if 1
     char carrier_path[512] = {'\0'};

     memset(buf, 0, sizeof(buf));
     snprintf(carrier_path, sizeof(carrier_path), "/sys/class/net/%s/carrier", hw_name);
     if ((fp = fopen(carrier_path, "r")) != NULL)
     {
         while (fgets(buf, sizeof(buf), fp) != NULL)
         {
             if (buf[0] == '0')
             {
                 status = IFSTATUS_DOWN;
             }
             else
             {
                 status = IFSTATUS_UP;
             }
         }
     }
     else
     {
         perror("Open carrier ");
     }
     fclose(fp);
 #endif

 //方法二：用函数吧！有点复杂，但是也是一种有效的办法
 #if 1
     int fd;

     if((fd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
     {
         perror("socket ");
         exit(0);
     }
     status = interface_detect_beat_ethtool(fd, hw_name);
     close(fd);
 #endif

     switch (status)
     {
         case IFSTATUS_UP:
             printf("%s : link up\n", hw_name);
             break;

         case IFSTATUS_DOWN:
             printf("%s : link down\n", hw_name);
             break;

         default:
             printf("Detect Error\n");
             break;
     }

     return 0;
 }