DllStruct ulong issue

[crashdemons]

okay, well, I'm having a little issue in one of my DLLStructs where changing one element of the struct, without changing the byte length, changes the value of all the elements that follow.

Technical details:

AutoIt 3.2.12.1

32-bit WinXP SP2.

Applied concepts/premises:

Data strings can by put into structures to format the data the way you want by loading it into a structure and creating another structure using the original struct's pointer.

Post by Smoke_N

---

ULong and UByte Var[4] both have a byte length of 4

Help File, DllStructGetData

ubyte 8bit(1byte) unsigned char

ulong 32bit(4bytes) unsigned integer

Tests, (see scripts attached below for more info on the "results")

Test A:

Here we declare a 5-element structure from the data loaded from a file (simulated here with a string)

and output the value of each element.

As you see the $FileData has been written so certain bytes should fall in certain struct fields, for ease of viewing.

-Expected results

i: 26985

j: 0x6a6a6a6a

data1: 11

data2: 22

value: vvvv

-Actual results

same as expected, this is our control group.

Test B:

Here we form a test exactly like Test A with the exception that 'ubyte j[4]' is now 'ulong j'

-Expected results

i: 26985

j: ? (0x6a6a6a6a as ulong)

data1: 11

data2: 22

value: vvvv

-Actual results

j: 825422090 (?)

data1: 22

data2: vv

value: vv&B

As you can see, the results from Test B don't exactly meet my expectations - am I at fault here for some misunderstanding?

Test scripts attached:

Edited September 20, 2008 by crashdemons

[martin]

expandcollapse popup

Global  $tStruct='align 2;short i;ulong j;ubyte data1[2];ubyte data2[2];ubyte value[4]'

$FileData='iijjjj1122vvvv';simulated for this PoC

$StructA=DllStructCreate('ubyte data[14]')
DllStructSetData($StructA,1,$FileData)
$PointerA=DllStructGetPtr($StructA)
$StructB=DllStructCreate($tStruct,$PointerA);put the FileData into the prefered structure, as posted in past threads

;i'd dispose of $StructA here, but doing so or ending it's existance
;(including closing a function) changes StructB's value - which is aggravating but unrelated to this issue

MsgBox(0,'StructB Values', _ 
'i: '&DllStructGetData($StructB,1)&@CRLF& _ 
'j: '& '0x' & Hex(DllStructGetData($StructB,2))&@CRLF& _ 
'data1: '&BinaryToString(DllStructGetData($StructB,3))&@CRLF& _ 
'data2: '&BinaryToString(DllStructGetData($StructB,4))&@CRLF& _
'value: '&BinaryToString(DllStructGetData($StructB,5)))
;====================================================================align 2
Global  $tStruct='short i;ubyte j[4];ubyte data1[2];ubyte data2[2];ubyte value[4]'

$FileData='iijjjj1122vvvv';simulated for this PoC

$StructA=DllStructCreate('ubyte data[14]')
DllStructSetData($StructA,1,$FileData)
$PointerA=DllStructGetPtr($StructA)
$StructB=DllStructCreate($tStruct,$PointerA);put the FileData into the prefered structure, as posted in past threads

;i'd dispose of $StructA here, but doing so or ending it's existance
;(including closing a function) changes StructB's value - which is aggravating but unrelated to this issue

MsgBox(0,'StructB Values', _ 
'i: '&DllStructGetData($StructB,1)&@CRLF& _ 
'j: '& DllStructGetData($StructB,2)&@CRLF& _ 
'data1: '&BinaryToString(DllStructGetData($StructB,3))&@CRLF& _ 
'data2: '&BinaryToString(DllStructGetData($StructB,4))&@CRLF& _
'value: '&BinaryToString(DllStructGetData($StructB,5)))

[crashdemons]

Thanks, that helps alot

- I see the small mention of 'align' in the help file with the example

By default, a structure alignment of 8 is used...

DllStructCreate("short;int"); structure is 8 bytes, the "int" is at offset 4
DllStructCreate("align 2;short;int"); structure is 6 bytes, the "int" is at offset 2

Although that didn't explain to me what was going on, or more importantly, which alignment to use when...

I read this article on Wikipedia about Data Structure alignment, but it didn't really help me visualize the process.

Edited September 23, 2008 by crashdemons