Question about structs

[ragdog]

Hello again

I have a little question about a struct i am little confused

Original code works not
or [eax]._struct.dwArray[ecx*4-6],

patch i with Olly to 4+4 works why?

or   dword ptr [eax+ecx*4+4],

4-6 is 2

and
4+4   8

or not?

Regards,

[zedd151]

We would need to see a little more code to know what you are trying to do...

[jj2007]

Tested with ML 6.14 ... 10.0 and JWasm:

Code Select Expand

include \masm32\include\masm32rt.inc

.data
rc RECT <12, 34, 56, 78>

.code

start:
mov edi, offset rc
m2m ebx, 2
print str$(rc.left), " = left", 13, 10
or [edi.RECT.left][ebx*4-8], -1
print str$(rc.left), " = left", 13, 10
print str$(rc.top), " = top", 13, 10
or [edi].RECT.left[ebx*4-4], -1
inkey str$(rc.top), " = top"
exit
end start

[sinsi]

4-6 is minus 2

[ragdog]

Yes that i think

but i can write as well

or [eax]._struct.dwArray[ecx*4-6]

to

or [eax]._struct.dwArray[ecx*2]  ??

[jj2007]

No.

[rrr314159]

I can't tell what the question is. Perhaps this will help?

All these give the same value, namely [eax]._struct.dwArray[2] :

IF ecx = 2: [eax]._struct.dwArray[ecx*4-6]
IF ecx = 1: [eax]._struct.dwArray[ecx*4-2]
IF ecx = 0: [eax]._struct.dwArray[ecx*4+2]

So by adjusting ecx appropriately any of these three expressions could be used

[dedndave]

you have to show us how "_struct" is defined

Code Select Expand

MYSTRUCT STRUCT
  stuff dd ?
MYSTRUCT STRUCT

that defines a structure type

Code Select Expand

    .data?
MyStruct MYSTRUCT <>

that defines a structure in the data? section

Code Select Expand

    mov     edx,offset MyStruct
    mov     eax,[edx].MYSTRUCT.stuff

or

Code Select Expand

    mov     eax,MyStruct.stuff

are both valid ways to acess it