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Index > Windows > open/read file (how ?)

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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

I am a king with asm (yes, it's true Razz Wink ) ,
but I have no knowledge about windows api. Embarassed

How to open a text file and copy its contents into memory ?

I have to open the file with the path ... ( Confused ???) ... a little help would be welcome!

thank you all.
Code:
i.e.
toto.txt = "abcde..."
virtualalloc ...
toto.txt ---> in memory
[eax] = "abcde .. " ; eax = result from virtualalloc
    


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Post 10 Aug 2010, 07:25
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Tyler



Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA
Tyler
CreateFile - to open
ReadFile - to read

Does that help? I get the feeling that I don't fully understand what you need.
Post 10 Aug 2010, 08:50
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji
Quote:
I don't fully understand what you need
load the contents of a file in memory.

This file contains a list of keywords which I would like to access.
For the moment I put this list in the data area, as a initialized variable,
but I would like to put this list in a file, then read that file and put this list of keywords in memory.
sorry for my bad english.

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Post 10 Aug 2010, 09:14
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sinsi



Joined: 10 Aug 2007
Posts: 696
Location: Adelaide
sinsi
The basic steps are usually
CreateFile
GetFileSize
GlobalAlloc
ReadFile
CloseHandle
Post 10 Aug 2010, 09:26
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ManOfSteel



Joined: 02 Feb 2005
Posts: 1154
ManOfSteel
ouadji wrote:
load the contents of a file in memory.

That's what the APIs mentioned by Tyler do. CreateFile can open an existing file and returns a handler. ReadFile uses this handler to read the file into a memory location pointed by lpBuffer.
This could be a simple buffer inside your application or it could be allocated using GlobalAlloc. GlobalAlloc returns a handler. GlobalLock uses this handler and returns the pointer you need.

Read the MSDN pages for these APIs and fill the parameters accordingly. And of course don't forget to clean up afterwards.
Post 10 Aug 2010, 09:35
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Tyler



Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA
Tyler
ouadji wrote:
Quote:
I don't fully understand what you need
load the contents of a file in memory.

This file contains a list of keywords which I would like to access.
For the moment I put this list in the data area, as a initialized variable,
but I would like to put this list in a file, then read that file and put this list of keywords in memory.
sorry for my bad english.
Nah man, your English is good Smile, I've heard it's pretty hard to learn for non-native speakers. I just thought you were asking for something more complex than I know. It was confusing to me why an asm master like yourself(Razz Wink) would be asking something I know the answer to. Very Happy

Just follow sinsi's list and it should work fine. MSDN(The site I linked to above.) is a good ref for WinAPI.
Post 10 Aug 2010, 09:50
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji
Quote:
Nah man, your English is good Smile
thank you, i do my best, it's not easy !

ok i beginning to understand.
Quote:
It was confusing to me why an asm master like yourself,would be asking something I know the answer to
Very Happy Very Happy Embarassed
yes indeed, api windows are a unknow world for me.

to allocate memory, i use "virtualalloc", as TG (like TG ?) in Fasmw.
...
last short question,
how to insert "simple db" in a text file
i.e. ... db 3h or db 17h
how to convert this : db 'abcde',00h,17h,03h ... in text ?
abcde ... ok ... but for 00h,17h,03h ???

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Post 10 Aug 2010, 10:07
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Tyler



Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA
Tyler
VirtualAlloc is for allocating whole pages, overkill for most memory allocations.

To insert text, you would just allocate "size_of_file"+"size_of_str_to_insert" the move/shift all that is to the right of the insertion "size_of_str_to_insert" to the right.

I suggest libc for moving/shifting the memory. memmove is made just for it.
Post 10 Aug 2010, 11:17
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia
vid
To write couple of bytes to file, use something like:
Code:
bytes_writted dd ?
string_to_write db "I hope I end up inside a file"
size_of_string = $ - string_to_write

...

push 0  ;overlapped - not needed
push offset bytes_written
push size_of_string
push string_to_write
push handle  ;handle is dword returned (in EAX) by CreateFileA
call [WriteFile]

;test if write succeeded
test eax, eax
jz error_on_write
    


Quote:
how to convert this : db 'abcde',00h,17h,03h ... in text ?

You mean you want to convert values 00h, 17h, 03h to their textual representations? (eg. strings "0", "23", "3", etc.?). You need to write a routine for that, or use one that already exists.

However, the most convenient way would be to use C API instead of Win32API, where you have the beautiful formatted I/O functions (eg. fprintf() in your case).
Post 10 Aug 2010, 11:29
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sinsi



Joined: 10 Aug 2007
Posts: 696
Location: Adelaide
sinsi
ManOfSteel, using GlobalAlloc with GMEM_FIXED means you don't need GlobalLock to get a pointer, this is returned by the GlobalAlloc call.
Post 10 Aug 2010, 11:47
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Picnic



Joined: 05 May 2007
Posts: 1288
Location: behind the arc
Picnic
ouadji wrote:
How to open a text file and copy its contents into memory ?


Hi ouadji,
Here is something very basic just to get you started.

Code:
        FileTitle db 'somefile.txt',0
        hFile dd ?
        nSize dd ?
        lpBytesRead dd ?
        lpBuffer rb 8192


        invoke  CreateFile, FileTitle, GENERIC_READ, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0
        ; TestApiError

        mov [hFile], eax

        invoke  GetFileSize, [hFile], 0
        ; TestApiError

        mov [nSize], eax

        invoke  ReadFile, [hFile], lpBuffer, [nSize], lpBytesRead, 0
        ; TestApiError

        invoke CloseHandle, [hFile]
    


A lightweight solution using fasm file directive. Smile
Code:
myfile:
        file 'somefile.txt'
        myfile.size = $-myfile  
    
Post 10 Aug 2010, 12:20
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji

thank you Picnic, vid, Tyler, sinsi, ManOfSteel Razz

I have enough information to get by!

again, thank you all.

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Post 10 Aug 2010, 13:20
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roboman



Joined: 03 Dec 2006
Posts: 122
Location: USA
roboman
ouadji wrote:

last short question,
how to insert "simple db" in a text file
i.e. ... db 3h or db 17h
how to convert this : db 'abcde',00h,17h,03h ... in text ?
abcde ... ok ... but for 00h,17h,03h ???


Well if you only need to make a couple of those files, you can just make a text file of db statements and run it through fasm. The other one I've done is to use a hex editor.
Post 10 Aug 2010, 14:05
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji
Quote:
you can just make a text file of db statements and run it through fasm.
I had not thought of !!!! Rolling Eyes
it's a perfect solution. I just tried, the result is exactly what I need.. Razz Razz
thank you roboman

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Post 10 Aug 2010, 15:02
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
Post 10 Aug 2010, 15:56
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ouadji



Joined: 24 Dec 2008
Posts: 1081
Location: Belgium
ouadji
This article about memory allocation is very interesting. (thank you LocoDelAssembly)
Personally, I like "VirtualAlloc" (from ring3) ...
yes, VirtualAlloc use page granularity
but I usually need large allocation, then this is not a problem.
I also like a memory allocation with page alignment.
(and from ring0, i use "ExAllocatePoolWithTag")

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Post 10 Aug 2010, 16:55
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