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Index > Windows > Picking up wrong error?

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moriman



Joined: 01 Apr 2006
Posts: 55
Location: Northern Ireland
moriman
I'm using the following routine to display any errors in my app. Unfortunately, the routine seems to be producing an error itself Rolling Eyes

Code:
ShowError:
   pushad
   invoke  GetLastError
   invoke  FormatMessage,\
              FORMAT_MESSAGE_FROM_SYSTEM+\
              FORMAT_MESSAGE_ALLOCATE_BUFFER,\  
              NULL,\                                                         
              eax,\                                                          
              LANG_NEUTRAL,\                                                 
              LErrStrBuff,\                                                  
              0,\                                                            
              NULL                                                           
   invoke  MessageBox,[hWnd],[LErrStrBuff],ErrTitle,MB_ICONERROR+MB_OK
   popad
   ret
    


However, when I induce a deliberate error (open a non-existant file or regkey, etc.), the MessageBox always states The parameter is incorrect. This happens no matter what value GetLastError returns in eax.

Any ideas Idea what's happening here?

many thanks Wink
Post 06 May 2006, 12:14
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7802
Location: Kraków, Poland
Tomasz Grysztar
This works just as expected:
Code:
format PE GUI 4.0
entry start

include 'win32a.inc'

section '.data' data readable writeable

ErrTitle db 'Error',0
LErrStrBuff dd ?

FileName db 'c:\nothing',0


section '.code' code readable executable

  start:

        invoke  CreateFile,FileName,GENERIC_READ,FILE_SHARE_READ,0,OPEN_EXISTING,0,0

        call    ShowError

        invoke  ExitProcess,0


ShowError:
   pushad
   invoke  GetLastError
   invoke  FormatMessage,\
              FORMAT_MESSAGE_FROM_SYSTEM+\
              FORMAT_MESSAGE_ALLOCATE_BUFFER,\  
              NULL,\                                                         
              eax,\                                                          
              LANG_NEUTRAL,\                                                 
              LErrStrBuff,\                                                  
              0,\                                                            
              NULL                                                           
   invoke  MessageBox,HWND_DESKTOP,[LErrStrBuff],ErrTitle,MB_ICONERROR+MB_OK
   popad
   ret

section '.idata' import data readable writeable

  library kernel32,'KERNEL32.DLL',user32,'USER32.DLL'

  include 'apia\kernel32.inc'
  include 'apia\user32.inc'    
Post 06 May 2006, 12:28
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moriman



Joined: 01 Apr 2006
Posts: 55
Location: Northern Ireland
moriman
Strange indeed¿ Yes, I tried this and get the correct error message.

In the attached routine the ShowError sub is only called from 2 places and the program skips the 2nd call because of the first error (RegOpenKey). When I close all programs and run test.exe from the Start->Run button (Win98), the first time it runs it produces the The parameter is incorrect error and starts the app (as it should). If I close the MessageBox and the app and then do the same again, it produces a The operation completed successfully error. LOL.
When I change your code above from
Code:
invoke  CreateFile,FileName,GENERIC_READ,FILE_SHARE_READ,0,OPEN_EXISTING,0,0
    

to
Code:
invoke  RegOpenKey, HKEY_CURRENT_USER, RegKey, RegHnd
    

I get the expected error string. Confused


Description:
Download
Filename: test.asm
Filesize: 4.65 KB
Downloaded: 51 Time(s)

Post 06 May 2006, 13:22
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7802
Location: Kraków, Poland
Tomasz Grysztar
It seems that RegOpenKey doesn't do SetLastError on failure, it just returns the error code in EAX. Checked it with OllyDbg.
Post 06 May 2006, 13:43
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moriman



Joined: 01 Apr 2006
Posts: 55
Location: Northern Ireland
moriman
Many thanks Tomasz, when I removed the invoke GetLastError, everything works as expected Smile
Post 06 May 2006, 14:26
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