擷取裝置mac地址

- (NSString *)macaddress{    int                 mib[6];    size_t              len;    char                *buf;    unsigned char       *ptr;    struct if_msghdr    *ifm;    struct sockaddr_dl  *sdl;        mib[0] = CTL_NET;    mib[1] = AF_ROUTE;    mib[2] = 0;    mib[3] = AF_LINK;    mib[4] = NET_RT_IFLIST;        if ((mib[5] = if_nametoindex("en0")) == 0) {        printf("Error: if_nametoindex error\n");        return NULL;    }        if (sysctl(mib,6, NULL, &len, NULL,0) < 0) {        printf("Error: sysctl, take 1\n");        return NULL;    }        if ((buf = malloc(len)) ==NULL) {        printf("Could not allocate memory. error!\n");        return NULL;    }        if (sysctl(mib,6, buf, &len, NULL, 0) < 0) {        printf("Error: sysctl, take 2");        free(buf);        return NULL;    }        ifm = (struct if_msghdr *)buf;    sdl = (struct sockaddr_dl *)(ifm +1);    ptr = (unsigned char *)LLADDR(sdl);    NSString *outstring = [NSStringstringWithFormat:@"%02X:%02X:%02X:%02X:%02X:%02X",                           *ptr, *(ptr+1), *(ptr+2), *(ptr+3), *(ptr+4), *(ptr+5)];    free(buf);        return outstring;}