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Index > DOS > Read / Write to file

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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
How do I write data to a file, that the user input into the console? Also, how do I read data from that file, and use the information in my program?

Here's a algorithm:

PROMPT "Enter name here: "
READ Name
STORE Name in File.txt
READ data from File.txt
PRINT data from text
;End-Of-Line

And now if the user input: John Doe, the program will store that into File.txt then read the data from that text file (which is John Doe), and then Print the data on screen

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meshnix
Post 27 Feb 2010, 03:53
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17714
Location: In your JS exploiting you and your system
revolution
MeshNix: Do you have a list of the DOS int 0x21 services?

http://en.wikipedia.org/wiki/MS-DOS_API
Post 27 Feb 2010, 03:56
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
Sort of!
Thanks!
Post 27 Feb 2010, 20:48
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cthug



Joined: 03 Apr 2009
Posts: 36
Location: /home/Australia
cthug
This is more complete and includes other Interrupts: Interrupt Jump Table.
Post 28 Feb 2010, 11:03
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
to read data from DOS files, i recommend to use this code:
Code:
fptr:
.off=0
.seg=2
.size=4
DOSread:
.call=0
.ptr=4
.name=8
.handle=12
        push eax ebx ecx edx edi esi ds
        mov edi,[esi+.ptr]
        mov edx,[esi+.name]   ; load the asciiz filename pointer
        mov edx,[edx]
        mov ax,3d00h         ; DOS open file
        int 21h
        jc .error             ; carry, then error
        mov [esi+.handle],ax
        mov bx,ax
        mov ax,[edi+fptr.seg]
        mov ds,ax
        mov dx,[edi+fptr.off] ; at [ds:dx]
        mov ah,3fh            ; will we load
        mov cx,0ffffh         ; ffffh bytes
        int 21h               ; from the file.
        jc .error             ; carry then error
        pop ds                ; restore ds
        mov [edi+fptr.size],eax   ; how long is the file, in bytes
        mov bx,[esi+.handle]
        mov ah,3eh            ; DOS close file
        int 21h
        jc .error
@@:
        pop esi edi edx ecx ebx eax
        ret
.error:
        mov word[esi+.handle],0
        mov eax,0
        jmp @b
    


it will open file withhandle, read from handle, and close file.
then, multiple file openings/ reopening are possible with a minimal effort.
Post 28 Feb 2010, 13:14
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
Ok. Thanks. I'll test it out and post
Post 01 Mar 2010, 02:59
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typedef



Joined: 25 Jul 2010
Posts: 2913
Location: 0x77760000
typedef
Just a question. I see people doing this. What does it do, whats its purpose ?


Quote:

Code:
push eax ebx ecx edx edi esi ds 
    

Post 17 Aug 2010, 19:56
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edfed



Joined: 20 Feb 2006
Posts: 4242
Location: 2018
edfed
it is because every registers can be modified in the function.
and it is writen one by one because sometimes, pushes are added or deleted during modifications.

and to avoid particular precautions in user code, everything is saved.

i hope people answered your question. Wink
Post 17 Aug 2010, 20:34
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typedef



Joined: 25 Jul 2010
Posts: 2913
Location: 0x77760000
typedef
yeah, thanks people.

*thought* Man, people are peoplelish *thought*
Post 17 Aug 2010, 20:48
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