ReturnType of structure for DLLCall

[brokenfox]

I'm calling a DLL that returns a Structure type. I can't figure out how to get this return type from the DLLCall function. I tried ptr thinking maybe I would just a ptr to the structure but that didn't work either.

Any help is appreciated.

[Juvigy]

Check out the

DllStructGetData ( Struct, Element [, index ] )

function

[brokenfox]

Check out the

DllStructGetData ( Struct, Element [, index ] )

function

I'm not sure I understand. Here's the code I was using to try and reference the structure from the ptr.

$inv ="ushort id;byte Index;uint count;uint Flag;uint Price;ushort extra"
$t = DllStructCreate($inv)
for $idx=1 to 2
    $t = dllcall($dll,"ptr:cdecl","GetItem","int",$face[0],"int",$idx)
    if not @error Then
        _DebugPrint("Loop index: " & $idx & _
                    "ID: " & DllStructGetData($t,"id")& _
                    "Index: " & DllStructGetData($t,"Index")& _
                    "count: " & DllStructGetData($t,"count")& _
                    "Flag: " & DllStructGetData($t,"Flag")& _
                    "Price: " & DllStructGetData($t,"Price")& _
                    "extra: " & DllStructGetData($t,"extra"))
    end if
next

and for reference here is the function prototype:

ITEMTYPE GetItem(void* Inst,  int Index)

and structure:

Public Structure ITEMTYPE
    Dim ID As UInt16
    Dim Index As Byte
    Dim Count As UInt32
    Dim Flag As UInt32
    Dim Price As UInt32
    Dim Extra As UInt16
End Structure

Edited February 18, 2010 by brokenfox

[Juvigy]

$t = dllcall($dll,"ptr:cdecl","GetItem","int",$face[0],"int",$idx)

Looks like here it doesnt work.

Try those instead:

$t = dllcall($dll,"int","GetItem","int",$face[0],"int",$idx)

$t = dllcall($dll,"int:cdecl","GetItem","int",$face[0],"int",$idx)

EDIT@

You can put DllStructGetSize(Struct) to check if the Struct has data

Edited February 18, 2010 by Juvigy

[Valik]

Yeah... whatever you're trying to use... find something else. Return types cannot be structures because the only code that ever returns a structure by value is amateur code written by somebody who doesn't know what they are doing. That function is a major performance bottleneck in whatever library you're trying to use. Best of all it doesn't even align on a proper boundary due to it's size so it's wasting even more time and effort copying 24 unused bits. Honestly, either contact the author and tell them to learn how to program or find something else that is written by someone who is a bit more competent.

AutoIt does not and should not support return structures because any library worth using is going to be written properly to return either pointers or take output pointers as parameters.

Edited February 18, 2010 by Valik
Typos suck.

[ProgAndy]

If you really have to use a structure as returntype, the structure is allocated by the called function.

Then the inly thing you have to do is wrapping this memory block in an AutoIt-DLLStruct:

$aRet = DLLCall(...)
$tStruct = DLLStructCreate($tagStruct, $aRet[0])

[Valik]

ProgAndy, it's being returned by value, not by pointer. AutoIt will truncate what is returned.

[ProgAndy]

Sorry. I missed this particular line with the function definition.

[brokenfox]

So, if it is going to truncate the returned value, then could I have it return char[x] sufficiently long enough to hold the data structure and then use DLLStructGetData with pointer to the returned char to get the data?

Also tried using dllcall($dll,"ushort;byte;uint;uint;uint;ushort:cdecl",....) but that didn't work.

Might have to scrap this and move back to VB.net as there is example code written for that but don't want to. Otherwise might have to find a different solution.

[PsaltyDS]

Where did this DLL come from? Got a link to its usage docs?

You're either ignoring, or didn't understand, what Valik told you, and that makes me wonder if the DLL really behaves as you described.

[Valik]

PsaltyDS, I expect the DLL does behave exactly as described. I can totally see a VB .NET programmer not understanding that returning by value is a performance problem I can totally see them not understanding that returning by-value means the structure has to maintain binary compatibility for all time or the caller will break if the structure is ever changed (unless the program is re-compiled against an identical version of the structure).