a question(too hard to explain in little amount of words...)

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windwakr

Joined: 30 Jun 2004
Posts: 827

windwakr 12 Jul 2004, 20:03

How do I do something like put an invoke into a string....what I mean is when I do an invoke how do I put the return into a string?
example:
I invoke getsystemmetrics,1.....how do I put that into a string?

Thanks

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12 Jul 2004, 20:03

coconut

Joined: 02 Apr 2004
Posts: 326
Location: US

coconut 13 Jul 2004, 04:28

most APIs that return a string actually return a pointer to a string buffer, probably eax. example:

Code:

format pe gui 4.0
entry start

include '%FASMINC%\win32a.inc'

_hello db 'hello world',0


  start:
        mov     eax, _hello
        invoke  MessageBox,0,eax,eax,0
        invoke  ExitProcess


;;
section '.idata' import data readable writeable

  library kernel,'KERNEL32.DLL',\
          user,'USER32.DLL'

  import kernel,\
         ExitProcess,'ExitProcess'

  import user,\
         MessageBox,'MessageBoxA'

any APIs like MessageBoxA that work with a pointer to a string buffer will take the returning buffer pointed at by eax. havent played with GetSystemMetrics myself but try maybe:

Code:


        invoke  GetSystemMetrics, 1
        mov     [buff], eax                ;return value/string buffer
        invoke  MessageBox,0,buff,buff,0

to format/process the string buffer you may have to play with various APIs like wsprintf, or perhaps search the boards for different string macros

13 Jul 2004, 04:28

wolf

Joined: 28 Sep 2003
Posts: 11

wolf 13 Jul 2004, 10:55

Perhaps you mean sth. like this:

Code:

section '.code' code readable writeable executable

start:
syscall GetSystemMetrics,SM_CXFULLSCREEN
stdcall dwtoa,eax,Buffer
syscall MessageBox,0,eax,Title,0
syscall ExitProcess,0

proc dwtoa,value,buff
     enterproc
        mov eax,[value]
        mov ecx,10
        mov edi,[buff]
        add edi,14
        mov byte[edi+1],0
     .loop:
        xor edx,edx
        test eax,eax
        je .finish
        div ecx
        add dl,'0'
        mov byte[edi],dl
        dec edi
        jmp .loop
     .finish:
       inc edi
       mov eax,edi
     endproc

Title db 'function result is:',0
Buffer rb 16

the dwtoa function is only for demonstration.

wolf

13 Jul 2004, 10:55

coconut

Joined: 02 Apr 2004
Posts: 326
Location: US

coconut 03 Aug 2004, 02:46

wolf, nice example on dwtoa. however it gives wierd results with negative numbers, was it meant to handle them?

03 Aug 2004, 02:46

VitalOne

Joined: 29 Jul 2003
Posts: 54
Location: USA

VitalOne 03 Aug 2004, 03:43

You can also use wsprintf API, like this

Code:

invoke wsprintf,string_buffer,"%d",eax

03 Aug 2004, 03:43

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