如何从DHCP服务器请求特定的IP地址？

1 回答

• 1

  根据我的假设，当您发现 dhcp 时，您需要IP地址 . 现在，例如 .

  如果使用 udhcpc (busybox:The udhcp client negotiates a lease with the DHCP server and notifies a set of scripts when a leases is obtained or lost.)* 我在接口wlan0上发现ip然后我首先写下系统调用以便在 wlan0 上启动发现

  system("udhcpc -i wlan0")
  

  然后打电话

  GetIpAddress_system(ipaddress);//for getting ip address
  

  如此简单的代码

  char ipaddress[16];
  system("udhcpc -i wlan0")
  GetIpAddress_system(ipaddress);//for getting ip address
  printf("\nip address:%s",ipaddress);
  

  找到 GetIpAddress_system() 的来源，如下所示

  static int GetIpAddress_system(char *myIp)
  {
      int retVal=0;
      int size  = 1;
      struct ifreq       *ifr;
      struct ifconf      ifc;
      struct sockaddr_in sa;
      char ip_add[24]={0};
      int serversocket;                        /* Socket */
  
      #define inaddrr(x) (*(struct in_addr *) &ifr->x[sizeof sa.sin_port])
      #define IFRSIZE   ((int)(size * sizeof (struct ifreq)))
      /* Create socket for receiving  */
      if ((serversocket = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0){
          printf("socket() failed");fflush(stdout);
          return -1;
      }
      else
      {
          ifc.ifc_len = IFRSIZE;
          ifc.ifc_req = NULL;
          do
          {
              ++size;
              /* realloc buffer size until no overflow occurs  */
              if (NULL == (ifc.ifc_req = realloc(ifc.ifc_req, IFRSIZE)))
              {
                  retVal= -1;
                  break;
              }
              ifc.ifc_len = IFRSIZE;
              if (ioctl(serversocket, SIOCGIFCONF, &ifc))
              {
                  perror("ioctl SIOCFIFCONF");
                  retVal = -1;
                  break;
              }
          }while(IFRSIZE <= ifc.ifc_len);
  
          if(0 == retVal)
          {
              ifr = ifc.ifc_req;
              for (;(char *) ifr < (char *) ifc.ifc_req + ifc.ifc_len; ++ifr)
              {
                  if (ifr->ifr_addr.sa_data == (ifr+1)->ifr_addr.sa_data)
                  {
                      continue;  /* duplicate, skip it */
                  }
                  if (ioctl(serversocket, SIOCGIFFLAGS, ifr))
                  {
                      continue;  /* failed to get flags, skip it */
                  }
                  if(strcmp(ifr->ifr_name,"wlan0") == 0)
                  {
                      strncpy(ip_add,inet_ntoa(inaddrr(ifr_addr.sa_data)),sizeof(ip_add));
                      break;
                  }
              }
          }
          close(serversocket);
      }
  
      if(0 == retVal)
      {
          printf("%s\n",ip_add);
          if(myIp)
          {
              memset(myIp,0,15);
              snprintf(myIp,15,"%s",ip_add);
          }
          if(ip_add[0])
          {
              return 0;
          }
          else
          {
              return -1;
          }
  
  
      }
      else
      {
          return -1;
      }
  }
  

  回复于 2024-04-27T15:19:57+08:00