DllStructCreate, alignment problem?

[j0kky]

Hi guys,

I'm trying to do with gethostbyname + inet_ntoa APIs the same thing that @IPAddress1234 macros do.

This is the code in C++:

struct hostent *remoteHost;
struct in_addr addr;
remoteHost = gethostbyname(NULL);
while (remoteHost->h_addr_list[i] != 0) {
    addr.s_addr = *(u_long *) remoteHost->h_addr_list[i++];
    printf("\tIPv4 Address #%d: %s\n", i, inet_ntoa(addr));
} 

I was able to convert it thanks to some old topics, this code returns a 16-bit block IP (192.168.x.x):

TCPStartup()
$pointer = DllCall("Ws2_32.dll", "ptr", "gethostbyname", "short", "")[0]
$hostent = DllStructCreate("ptr h_name; ptr h_aliases; short h_addrtype; short h_length; ptr h_addr_list", $pointer)
$sh_addr_list = DllStructCreate("ptr", DllStructGetData($hostent, "h_addr_list"))
$inaddr = DllStructCreate("ULONG", DllStructGetData($sh_addr_list, 1))
$uint = DllStructGetData($inaddr,1)
ConsoleWrite(DllCall("Ws2_32.dll", "str", "inet_ntoa", "UINT", $uint)[0] & @CRLF)
TCPShutdown()

But I really don't understand why it is necessary to add this intermediate step:

$sh_addr_list = DllStructCreate("ptr", DllStructGetData($hostent, 5))

For example, this code returns a sort of 20-bit block IP (172.x.x.x) with a variable third and fourth octet.

TCPStartup()
$pointer = DllCall("Ws2_32.dll", "ptr", "gethostbyname", "short", "")[0]
$hostent = DllStructCreate("ptr h_name; ptr h_aliases; short h_addrtype; short h_length; ptr h_addr_list", $pointer)
$inaddr = DllStructCreate("ULONG", DllStructGetData($hostent, "h_addr_list"))
$uint = DllStructGetData($inaddr,1)
ConsoleWrite(DllCall("Ws2_32.dll", "str", "inet_ntoa", "UINT", $uint)[0] & @CRLF)
TCPShutdown()

I think it is a problem about the structure alignment but I'm not sure, someone of you can explain it to me?

Thank to all!

Edited October 24, 2014 by j0kky

[Danyfirex]

because it's a pointer to a pointer.

so. There is not alignment problem.

saludos

Edited October 24, 2014 by Danyfirex

[j0kky]

It is clear.

Buuut why is a pointer to a pointer needed? Where is written in MSDN documentation that inet_ntoa needs a pointer to a pointer argument?

EDIT:

In few words, if I didn't try the topic that put me in the right way, how can I write the right code?

Edited October 24, 2014 by j0kky

[Danyfirex]

Your way is correct.

h_addr_list is a array of pointers.(C way).

In autoit just jump 4 byte forward.

inet_ntoa need a pointer to in_addr.

h_addr_list are serverals n_addr structure by its pointer.

Saludos

Edited October 24, 2014 by Danyfirex

[Danyfirex]

Another thing gethostbyname need a const char *name not a short.

Saludos

[j0kky]

In autoit just jump 4 byte forward.

This is a precious information! And I have never tried it in the Autoit help file.

But I still don't understand why I need to use a pointer to a pointer. Why doesn't it work using just the pointer DllStructGetData($hostent, "h_addr_list")? (first I used this way, as in script 2, but it didn't work)

Sorry for the insistence but I'm realizing I've a lack of knowledge on this topic and I would like to fill it.

Edited October 24, 2014 by j0kky

[Danyfirex]

Becuase You're passing the array pointer. not the first array[0] value.

TCPStartup()
$pointer = DllCall("Ws2_32.dll", "ptr", "gethostbyname", "str", "")
$pointer=$pointer[0]
$hostent = DllStructCreate("ptr h_name; ptr h_aliases; short h_addrtype; short h_length;ptr h_addr_list", $pointer)
$sh_addr_list = DllStructCreate("ptr", DllStructGetData($hostent, "h_addr_list")) ;We get the Pointer to an array of addr 
$inaddr = DllStructCreate("ptr", DllStructGetData($sh_addr_list, 1));we get the array[0] ;if you want to get another index just plus 4
$uint = DllStructGetData($inaddr,1)
$ret=DllCall("Ws2_32.dll", "str", "inet_ntoa", "UINT", $uint)
ConsoleWrite( $ret[0] & @CRLF)
TCPShutdown()

Edit:

saludos

Edited October 24, 2014 by Danyfirex

[j0kky]

Thank you very much!!! I think I've got it!

Just to resume from your last script:

DllStructGetData($hostent, "h_addr_list") -> "h_addr_list" array, as in C it has the first array element value (h_addr_list[0])

DllStructGetData($sh_addr_list, 1) -> pointer to "h_addr_list" array first element (h_addr_list[0])

Just the last question, I promise : in this particular situation, aren't they both equal to h_addr_list[0]?

[Danyfirex]

DllStructGetData($hostent, "h_addr_list") -> "h_addr_list" array, as in C it has the first array element value (h_addr_list[0])
 
Here I got the Pointer to the pointer(the array). 

 
DllStructGetData($sh_addr_list, 1) should be h_addr_list[0]
 
Saludos

[jguinch]

Nice useful examples...

BTW, here is a good example from funkey using getaddrinfo :

It can also help you ?