Linux C程序如何检测WIFI无线USB网卡是否可用？

最新做一个WIFI应用项目。如何检测WIFI USB设备是否插上了呢？特此共享。第一种方法，采用读取文件的方式。在linux下，任何一种设备都可看成文件。通过分析相关文件信息，可得知WIFI设备是否存在；代码示例如下：    static void WIFI_Enum_Device（void）
{
    char  buff[1024];
    FILE * fh;     /* Check if /proc/net/wireless is available */
    fh = fopen（PROC_NET_WIRELESS, "r"）;
    if（fh ！= NULL）
    {
        /* Success : use data from /proc/net/wireless */        /* Eat 2 lines of header */
        fgets（buff, sizeof（buff）, fh）;
        fgets（buff, sizeof（buff）, fh）;        /* Read each device line */
        while（fgets（buff, sizeof（buff）, fh））
        {
            char name[IFNAMSIZ + 1];
            char *s;            /* Skip empty or almost empty lines. It seems that in some
            * cases fgets return a line with only a newline. */
            if（（buff[0] == ""） || （buff[1] == ""））
                continue;            /* Extract interface name */
            s = WIFI_Get_DeviceName（name, sizeof（name）, buff）;            if（！s）
            {
            /* Failed to parse, complain and continue */
#ifndef IW_RESTRIC_ENUM
                fprintf（stderr, "Cannot parse " PROC_NET_DEV " "）;
#else
                fprintf（stderr, "Cannot parse " PROC_NET_WIRELESS " "）;
#endif
            }
            else
                /* Got it, save the name about this interface */            {//we always use the first detected device when doing first time detecting
                if（s_DeviceCount == 0）
                {
                    if（strcmp（s_Deviceinfo.DeviceName,name））
                    {
                        memset（（char *）&s_Deviceinfo, 0, sizeof（DeviceInfo_t））;                        memcpy（s_Deviceinfo.DeviceName,name,IFNAMSIZ）;
                    }
                    if（strlen（s_SavedDevice） == 0）//this is the first detected device when doing first time detecting, we save it
                        memcpy（s_SavedDevice,name,IFNAMSIZ）;
                }
                else
                {//there is more than one device, we should use the first detected
                    if（！strcmp（s_SavedDevice,name））
                    {
                        memset（（char *）&s_Deviceinfo, 0, sizeof（DeviceInfo_t））;                        memcpy（s_Deviceinfo.DeviceName,name,IFNAMSIZ）;
                    }
                }
                s_DeviceCount++;
            }
        }        fclose（fh）;
    }

} static char* WIFI_Get_DeviceName（char * name, /* Where to store the name */
       int nsize, /* Size of name buffer */
       char * buf） /* Current position in buffer */
{
    char * end;    /* Skip leading spaces */
    while（isspace（*buf））
        buf++;#ifndef IW_RESTRIC_ENUM
    /* Get name up to the last ":". Aliases may contain ":" in them,
    * but the last one should be the separator */
    end = strrchr（buf, ":"）;
#else
    /* Get name up to ": "
    * Note : we compare to ": " to make sure to process aliased interfaces
    * properly. Doesn"t work on /proc/net/dev, because it doesn"t guarantee
    * a " " after the ":"*/
    end = strstr（buf, ": "）;
#endif    /* Not found ？？？ To big ？？？ */
    if（（end == NULL） || （（（end - buf） + 1） > nsize））
        return（NULL）;    /* Copy */
    memcpy（name, buf, （end - buf））;
    name[end - buf] = "";    /* Return value currently unused, just make sure it"s non-NULL */
    return（end）;
} RETURN_TYPE APP_WIFI_DetectDevice（void）
{
    char command[50] = {""};
    s_DeviceCount = 0; //reset count
    WIFI_Enum_Device（）;
    s_LastDeviceCount = s_DeviceCount;
    if（s_DeviceCount > 0）
    {
        sprintf（command,"ifconfig %s up",s_Deviceinfo.DeviceName）;
        system（command）; //boot up the device firstly
        return SYS_NOERROR;
    }
    else
        return SYS_FAILED;
}      第二种方法，利用linux ioctl函数读取I/O接口的相关信息。 /*****************************************************************************
* Name        : trid_char * APP_NetLink_GetIFFLAGS（char *NetDev ）
* Description : Get net interface IFFLAGS
* Params      : NetDev
* Returns     : the string of the NetDev
* Author/date : Danny.Hu /2011.11.16
*****************************************************************************/
RETURN_TYPE APP_NetLink_GetIFFlags（ trid_char *NetDev ）
{
    int fd = -1;
    int InterfaceFlags;
    struct ifreq ifr;
    memset（&ifr, 0, sizeof（ifr））;
    strcpy（ifr.ifr_name, NetDev）;
    fd = socket（AF_INET, SOCK_DGRAM, 0）;
    if （fd < 0）
    {
        printf（"Cannot get control socket "）;
        close（fd）;
        return SYS_FAILED;
    }
    else if（ 0！=（ioctl（fd, SIOCGIFFLAGS, （char*）&ifr）））
    {
       printf（"Cannot get Network Interface Flags！ "）;
       close（fd）;
       return SYS_FAILED;
    }

    InterfaceFlags = ifr.ifr_flags;

    printf（"<"）;
    if （ InterfaceFlags & IFF_UP）                       printf（"Network %s is UP, ", NetDev）;
    if （ InterfaceFlags & IFF_BROADCAST）     printf（"Network %s is BCAST, ", NetDev）;
    if （ InterfaceFlags & IFF_MULTICAST）      printf（"Network %s is MCAST, ", NetDev）;
    if （ InterfaceFlags & IFF_LOOPBACK）       printf（"Network %s is LOOP, ", NetDev）;
    if （ InterfaceFlags & IFF_POINTOPOINT）   printf（"Network %s is P2P, ", NetDev）;
    printf（"> "）;
    close（fd）;
    return SYS_NOERROR;
}