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From: almas on 14 Apr 2008 17:40
Hello.
I ofen need help... but, this day, i built a COm alone.
The aim : Open a file, modify bytes, write it in an other file.
Now, i just write 256 bytes, just for test.
Next step : modify particular Ascii.
Then use largers files.
Below, my usefull code.
If you have betters methods, , sure i will apprecate.
Best Regards Almas

mov ax, 3D12h
mov dx, offset input
int 21h
mov offset handle1, ax
mov bx, [offset handle1] ; A86 need this syntax !
mov ah, 3Fh
mov cx,100h ; read 256 Bytes
mov dx, offset address ; buffer
int 21h
cmp ax,0 ; End of File ?
ja continue
int 20h
continue:
mov cx,ax ; Nbr of bytes usefull if less than 256
mov offset size_byte, ax ; rescue the size
mov si, offset address ; change bytes in buffer
mloop:
add byte [si],20h
inc si ; modify here...
loop mloop
jmp short do_it

creat_fil:
mov ah,3Ch
mov dx,offset output
xor cx,cx ; attrib
int 21h
do_it:
mov ax,3D01h ; Open for Write
mov dx, offset output
int 21h
jb creat_fil ; if not exist
mov offset handle2,ax
mov bx, [offset handle2]
mov ax,4202h
xor cx,cx
xor dx,dx ; BX keeps same value
int 21h
; mov dx,ax ; size, give an offset
xor dx,dx ; begin a byte 0
mov ax,4200h
xor cx,cx
int 21h
mov ah,40h
mov cx, [offset size_byte]
mov dx, offset address
int 21h
mov ah,3Eh
int 21h ; BX keep value Handle2

mov bx, [offset handle1] ; close first file
mov ah, 3Eh
int 21h
int 20h
; data -----------
size_byte db: ,0,0,0,0
input db: "FILE.IN" ,0
output db: "FILE.OUT" ,0
handle1 db: ,0,0,0,0
handle2 db: ,0,0,0,0
address:
db: ,0,0,0,0,0,0


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