Checking error codes

[SCHiM]

I've been learning asm for quite some time now
And I've been trying to open, and read the contents of a file for a while now
But something's wrong, and I cannot check the error codes to see what

How can I check (print) the error codes my program gives me
I've tried printing them to a console, and through a message box, the first prints a character on my screen and the second method fails
Here's the code I'm using:

Code Select Expand

.386
.model flat,stdcall
option casemap:none

include     \masm32\include\windows.inc
include     \masm32\include\kernel32.inc
include     \masm32\include\user32.inc
include     \masm32\include\masm32.inc

includelib      \masm32\lib\kernel32.lib
includelib      \masm32\lib\user32.lib
includelib  \masm32\lib\masm32.lib



.data

txt db "There was an error with reading the file requested",0
capt db "SCHiM"
buffer db 1000 dup(0)
fname db "cmd.txt",0
err dd 0


.data?

hFile HANDLE <?>

BsRead dd <?>

.code
start:


invoke CreateFile, addr fname, GENERIC_ALL, 0, 0, 4, FILE_ATTRIBUTE_NORMAL, 0
mov hFile, eax

invoke ReadFile, addr hFile, addr buffer, 150, addr BsRead, 0

cmp eax, 0
jne nerr

invoke GetLastError
  mov err, eax

invoke   AllocConsole
invoke StdOut, addr err

;invoke  MessageBox,0, er,ADDR capt,MB_OK   


nerr:

invoke MessageBox, 0, addr buffer, addr capt, MB_OK

invoke ExitProcess, 0

end start

Thanks in advance
-SCHiM

[Coma]

Hi,
GetLastError retrurns a value, nothing more, i.e. not a pointer !
That is the reason that you can see a character on the screen.
The MessageBox needs a pointer to a buffer not a value.

Try this (for win32 errors):

BufferError             db MAX_PATH     dup (?)

invoke  GetLastError ;returns error value in EAX
invoke  FormatMessage,FORMAT_MESSAGE_FROM_SYSTEM,0,eax,0,ADDR BufferError,MAX_PATH,0 ;returns error message in BufferError
invoke  MessageBox,0,ADDR BufferError,ADDR capt,MB_OK ;display error message

[SCHiM]

Thank you for your fast reply!
I'll use this from now on insead of using a debugger

But I've another guestion
Create file succeeds, and as far as I can see returns a vailid handle to my file however When I'm arriving at ReadFile I get an "ERROR_INVAILID_HANDLE"

Why is that? Nothing is wrong is there, here's the code I'm currently using:

Code Select Expand

.386
.model flat,stdcall
option casemap:none

include     \masm32\include\windows.inc
include     \masm32\include\kernel32.inc
include     \masm32\include\user32.inc
include     \masm32\include\masm32.inc

includelib      \masm32\lib\kernel32.lib
includelib      \masm32\lib\user32.lib
includelib  \masm32\lib\masm32.lib



.data

txt db "There was an error with opening the file requested",0
capt db "SCHiM"
buffer db 1000 dup(0)
fname db "cmd.txt",0
err dd 0


.data?

hFile HANDLE <?>

BsRead dd <?>

.code
start:


invoke CreateFile, addr fname, GENERIC_ALL, 0, 0, 4, FILE_ATTRIBUTE_NORMAL, 0
cmp eax,INVALID_HANDLE_VALUE
jne nerr


invoke MessageBox, 0, addr txt, addr capt, MB_OK






nerr:
mov hFile, eax
invoke ReadFile, addr hFile, addr buffer, 11, addr BsRead, 0
invoke MessageBox, 0, addr buffer, addr capt, MB_OK

invoke ExitProcess, 0

end start

Solved by myself

I was having the ussual problems with reading my own code, and understanding what I was doing...
Instead of passing a handle to ReadFile() I passed a pointer to a handle: addr hFile, it should be: hFile

-SCHiM

[Coma]

Hi,
in the ReadFile function do not use ADDR hFile, use hFile.

When you are finished with a file operation you must always close the handle.

invoke CloseHandle,hObject

The handle (hObject) is returned by the CreateFile function in EAX.

Example:
invoke  CreateFile,ADDR BufferFile,GENERIC_READ,FILE_SHARE_READ,0,OPEN_EXISTING,FILE_ATTRIBUTE_NORMAL,0
cmp     eax,INVALID_HANDLE_VALUE
je      ErrorHandling
mov     hFile,eax
invoke  ReadFile,hFile,pMem,FileBytesTotal,ADDR FileBytesRead,0
cmp     eax,0
je      ErrorHandling
cmp     FileBytesRead,0
je      ErrorHandling
invoke  CloseHandle,hFile