C：如何将 char 数组复制到结构 ifreq？

Question

Unable to copy a char array to struct ifreq s. Below is the declaration which has been defined,

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

char interface[100];//="wlp1s0";
char reader_mac[13] = {00};

int main()
{
  FILE *f = popen("ip addr show | awk '/inet.*brd/{print $NF}'", "r");
  while (fgets(interface, 100, f) != NULL) {
  }
  strtok(interface, "\n");  // kaylum's Suggestion from the comments below
  printf( "interface :: %s\n", interface);
  pclose(f);

  struct ifreq s;    
  int fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);  


  strcpy(s.ifr_name, interface);
  // strcpy(s.ifr_name, "wlp1s0");


  if (0 == ioctl(fd, SIOCGIFHWADDR, &s)) {
  int i;

  for (i = 0; i < 6; ++i){
    unsigned char data  =  s.ifr_addr.sa_data[i];
    // printf("ddd:::%02x\n", data );
    sprintf(reader_mac+(i*2), "%02x", data);
  }
  reader_mac[12] = '\0';
  printf("reader_mac ::: %s\n",reader_mac);
}
}

Now, while copying the interface to s.ifr_name, I am unable to retrieve the given interface's mac address, whereas if i replace strcpy(s.ifr_name, interface) as strcpy(s.ifr_name,"wlp1s0"), the same is able to return the mac address.

I can able to retrieve the active network interfaces using system command,

interface :: wlp1s0

Whereas, the retrieved network interface is passed to strcpy() to copy the interface to s.ifr_name, I am unable to retrieve the mac address.

How this has to be addressed here?

kaylum's Suggestion from the comments:

After adding strtok(interface, "\n"); in the above script, it is not able to retrieve the mac address.

reader_mac ::: fc017c0f2b75

Answer 1

From the fgets manual :

If a newline is read, it is stored into the buffer

So interface may contain the trailing newline which would confuse the ioctl . Use any method to first strip the \n before passing to ioctl. For example:

if ((p=strchr(interface, '\n')) != NULL) {
    *p = '\0';
}