C and C++ is used to detect the state of network interface under linux

The example of this paper shares the status of network interface detection under C/C++ for your reference. The specific content is as follows

To write something that detects the state of the network interface, but does not like to constantly ping other address, also do not want to call another command line tool to do this, so after google n content failed, searched the source code of a detection tool.

The following code was debuggable under fedora 9 / CentOS 5.2 :)

#include <sys/types.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <stdio.h>
#include <errno.h>
#include <net/if.h>
 
struct ethtool_value 
{
 __uint32_t cmd;
 __uint32_t data;
};
 
/*return 1:has cable; return 0:no cable*/
int detect_eth_cable(char *ifname) 
{
 struct ethtool_value edata;
 struct ifreq ifr;
 int fd = -1, err = 0;
 
 memset(&ifr, 0, sizeof(ifr));
 strcpy(ifr.ifr_name, ifname);
 
 fd = socket(AF_INET, SOCK_DGRAM, 0);
 if (fd < 0) {
  //perror("Cannot get control socket");
  return -1;
  }
 edata.cmd = 0x0000000A;
 ifr.ifr_data = (caddr_t)&edata;
 err = ioctl(fd, 0x8946, &ifr);
 if (err == 0) {
  fprintf(stdout, "Link detected: %s\n", edata.data ? "yes":"no");
 } else if (errno != EOPNOTSUPP) {
  perror("Cannot get link status");
  }
 return(edata.data==1 ? 1:0);
}
int main(int argc, char**argv)
{
 detect_eth_cable("p1p1");
 return 0;
}

Other codes:

int get_netportstatus(const char *interface) {
 char cmd[1024];
 char *tt;
 FILE *fp;
 int devflag;
 devflag=get_netflag(interface);
 if (devflag==DEV_DOWN) {
 sprintf(cmd,"ifconfig %s up",interface);
 system(cmd);
 }
 sprintf(cmd,"ethtool %s | grep \"Link detected\" > /tmp/eth.temp",interface);
 system(cmd);
 if (devflag==DEV_DOWN) {
 sprintf(cmd,"ifconfig %s down",interface);
 system(cmd);
 }
 fp=fopen("/tmp/eth.temp","r");
 if (fp==NULL) {
 system("rm -rf /tmp/eth.temp");
 return -1;
 }
 fgets(cmd,1024,fp);
 fclose(fp);
 system("rm -rf /tmp/eth.temp");
 tt=strstr(cmd,"no");
 if (tt!=NULL) return LINK_DOWN;
 tt=strstr(cmd,"yes");
 if (tt!=NULL) return LINK_UP;
 return -1;
}

#include <sys/types.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <stdio.h>
#include <errno.h>
#include <net/if.h>
 
 
struct ethtool_value {
  __uint32_t  cmd;
  __uint32_t  data;
};
 
 
int main(int , char* [])
{
 struct ethtool_value edata;
 int fd = -1, err = 0;
 struct ifreq ifr;
 
 
  memset(&ifr, 0, sizeof(ifr));
  strcpy(ifr.ifr_name, "eth0");
  fd = socket(AF_INET, SOCK_DGRAM, 0);
  if (fd < 0) {
    perror("Cannot get control socket");
    return 70;
  }
  edata.cmd = 0x0000000a;
  ifr.ifr_data = (caddr_t)&edata;
  err = ioctl(fd, 0x8946, &ifr);
  if (err == 0) {
    fprintf(stdout, "Link detected: %s\n",
      edata.data ? "yes":"no");
  } else if (errno != EOPNOTSUPP) {
    perror("Cannot get link status");
  }
 return 0;
}

#include <net if.h=""> // IFF_RUNNING
 
// If the network card has face cable, return 0 Otherwise return -1.
int check_nic(char *nic)
{
 struct ifreq ifr;
 int skfd = socket(AF_INET, SOCK_DGRAM, 0);
 
 strcpy(ifr.ifr_name, nic_name);
 if (ioctl(skfd, SIOCGIFFLAGS, &ifr) < 0)
 {
  return -1;
 }
 if(ifr.ifr_flags & IFF_RUNNING)
  return 0; //  The network card is plugged in 
 else return -1;
}
</net>