Hello, this is a very stupid question but I just can't figure it out. How should I use the dp in the data segment ? I tried like this but it gave an error when I tried to compile.
rect dd 0 dp(4)
I just want 4 duplicates of this 0 value.
Thanks in advance
Jannes
Jannes,
Quote from: gelatine1 on June 25, 2014, 07:15:57 PM
Hello, this is a very stupid question but I just can't figure it out. How should I use the dp in the data segment ? I tried like this but it gave an error when I tried to compile.
rect dd 0 dp(4)
I just want 4 duplicates of this 0 value.
Thanks in advance
Jannes
your question isn't clear for me. Do you mean the dup operator? If so, it's a syntax question.
Gunther
Ohhh Yes I think I meant dup and yes indeed it's a syntax question. I'm not sure how to use it.
Here is an example. Launch the exe with Olly and see what it does...
include \masm32\include\masm32rt.inc
.data?
rc RECT 5 dup(<>)
.code
start:
mov eax, offset rc
mov ecx, offset rc.top
mov edx, rc[0*RECT].right
mov edx, rc[1*RECT].right
mov edx, rc[2*RECT].right
exit
end start
Oh yes I see :) If I want to declare 4 dwords containing 0 then I should use
rect dd 4 dup(0) instead of rect dd 0 dup(4).
Thanks for the help guys
that will work
however, for rectangles, we generally use a RECT structure
http://msdn.microsoft.com/en-us/library/dd162897%28v=vs.85%29.aspx (http://msdn.microsoft.com/en-us/library/dd162897%28v=vs.85%29.aspx)
most of the MS structures are defined for you in windows.inc
RECT STRUCT
left dd ?
top dd ?
right dd ?
bottom dd ?
RECT ENDS
now, you can do something similar to what Jochen showed you
however - his code creates 5 RECT structures :biggrin:
you probably only need one
this will create an uninitialized RECT
we usually place it in the .DATA or .DATA? section
rc RECT <>
if you would like to, you may initialize the structure (.DATA section)
it has 4 members, so....
rc RECT <10,25,30,35>
you may access the members as
mov eax,rc.right
or, use a register for the address and
mov edx,offset rc
mov eax,[edx].RECT.right
Quote from: dedndave on June 25, 2014, 09:52:56 PMor, use a register for the address and
mov edx,offset rc
mov eax,[edx].RECT.right
This is indeed a good solution because its encoding is much smaller than for a global rc.right (for example). Typically, you would use a non-volatile register such as esi, edi, ebx.
That's all not bad but back to the question of DUP. One can use, for example:
db 128 dup (?)
That statement would reserve 128 bytes with arbitrary content.
Gunther
Gunther,
I'm not sure how this is so, because the listing shows that the reserved bytes are in the .data section, but in my tests under Windows the reserved bytes were zeroed.
deleted
Quote from: MichaelW on June 26, 2014, 06:55:44 AM
I'm not sure how this is so, because the listing shows that the reserved bytes are in the .data section, but in my tests under Windows the reserved bytes were zeroed.
Either a design decision or a feature of Windows. An error is unthinkable. But joke apart, it's interesting to know.
Gunther