An example of SIZEOF

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BoR0

Joined: 12 Nov 2004
Posts: 31

BoR0

I tried all, even googling.
I just cant sort it out. Crying or Very sad

Please give me some example of how to use it and all the needed include files.

09 Feb 2005, 13:34

gumletis

Joined: 18 Dec 2004
Posts: 128

gumletis

mov eax,string
call getsize ; Get size of eax and overwrite it to eax

RET
getsize:
push esi
mov esi,0
@@:
inc esi
cmp byte[eax+esi],0
jne @B
mov eax,esi
pop esi
RET

09 Feb 2005, 14:21

decard

Joined: 11 Sep 2003
Posts: 1092
Location: Poland

decard

sizeof is declared by structure macros when you define a new structure:

Code:

struct my_structure
   field_1 dd ?
   field_2 rb 128
ends

after this definition you can use sizeof.my_structure to obtain number of bytes that structure occupies.

09 Feb 2005, 15:50

Vasilev Vjacheslav

Joined: 11 Aug 2004
Posts: 392

Vasilev Vjacheslav

or this:

Code:

proc _strlen, string
  mov     edi,[string]
        cld
 xor     eax,eax
     or      ecx,-1
      repne   scasb
       not     ecx
 dec     ecx
        xchg    ecx,eax
      return
endp

eax - length of string

09 Feb 2005, 15:54

gumletis

Joined: 18 Dec 2004
Posts: 128

gumletis

hmm vasilev v nice code :-s donno how to use not... :-s

10 Feb 2005, 18:27

BoR0

Joined: 12 Nov 2004
Posts: 31

BoR0

decard, you got it right! that is my point!

Sorry guys, I already know of the string length algo, that was not my point though.

BTW, why does sizeof works for structures only?

I tried

Code:

section '.code' code readable executable
mov eax, sizeof.my_structure
invoke ExitProcess, 0

section '.data' data readable writeable
my_structure dd ?

and it didn't assemble Sad

please reply!

10 Feb 2005, 19:00

decard

Joined: 11 Sep 2003
Posts: 1092
Location: Poland

decard

sizeof is defined by struct macro (it is a macro, not a built-in keyword; built-in is named "struc"). That's why it isn't defined by "dd" directive. You have just to remember that it has 4 bytes Wink

maybe some macro expert could think of some solution Smile

10 Feb 2005, 19:22

BoR0

Joined: 12 Nov 2004
Posts: 31

BoR0

Well I personally think that it is a good idea to make SIZEOF work for all types of variables.. I mean, its an option that almost EVERY assembler supports it.

Thanks for all your help and kindness Smile

10 Feb 2005, 21:15

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