C - 如何將 char 轉換為字符串以傳遞 strcpy？

Question

我需要使用系統命令以 c 語言獲取設備的活動網絡接口，並且必須傳遞系統響應以獲取設備的 MAC 地址，同樣，以下是我一直在使用的示例，

#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];
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) {
  }
  printf( "interface :: %s\n", interface );
  pclose(f);  

  struct ifreq s;    
  int fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_IP);  
  // strcpy(s.ifr_name, "eth0");
  strcpy(s.ifr_name, interface);
  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);
}
}

如何解決這個問題？

我可以獲得活動界面，

interface :: wlp1s0

然而，相同的接口被傳遞給 strcpy(s.ifr_name, interface) 並且無法獲得地址。 而不是 strcpy(s.ifr_name, interface)，如果我將它用作 strcpy(s.ifr_name, "wlp1s0)，同樣返回 mac 地址，沒有任何問題。

Answer 1

Yes, you can parse the output of ip addr show , but wait, what if the implementer changes the way ip addr show produces the output. 它的 output 尚未標准化。 您是否考慮過使用getifaddrs() ？ 以下代碼來自他們的手冊頁：

#define _GNU_SOURCE     /* To get defns of NI_MAXSERV and NI_MAXHOST */
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/if_link.h>

int main(int argc, char *argv[])
{
   struct ifaddrs *ifaddr, *ifa;
   int family, s;
   char host[NI_MAXHOST];

   if (getifaddrs(&ifaddr) == -1) {
       perror("getifaddrs");
       exit(EXIT_FAILURE);
   }

   /* Walk through linked list, maintaining head pointer so we
      can free list later */

   for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
       if (ifa->ifa_addr == NULL)
           continue;

       family = ifa->ifa_addr->sa_family;

       /* Display interface name and family (including symbolic
          form of the latter for the common families) */

       printf("%-8s %s (%d)\n",
              ifa->ifa_name,
              (family == AF_PACKET) ? "AF_PACKET" :
              (family == AF_INET) ? "AF_INET" :
              (family == AF_INET6) ? "AF_INET6" : "???",
              family);

       /* For an AF_INET* interface address, display the address */

       if (family == AF_INET || family == AF_INET6) {
           s = getnameinfo(ifa->ifa_addr,
                   (family == AF_INET) ? sizeof(struct sockaddr_in) :
                                         sizeof(struct sockaddr_in6),
                   host, NI_MAXHOST,
                   NULL, 0, NI_NUMERICHOST);
           if (s != 0) {
               printf("getnameinfo() failed: %s\n", gai_strerror(s));
               exit(EXIT_FAILURE);
           }

           printf("\t\taddress: <%s>\n", host);

       } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
           struct rtnl_link_stats *stats = ifa->ifa_data;

           printf("\t\ttx_packets = %10u; rx_packets = %10u\n"
                  "\t\ttx_bytes   = %10u; rx_bytes   = %10u\n",
                  stats->tx_packets, stats->rx_packets,
                  stats->tx_bytes, stats->rx_bytes);
       }
   }

   freeifaddrs(ifaddr);
   exit(EXIT_SUCCESS);
}