Re: opening and reading a character from a file with emu8086 assembler


<spamtrap@xxxxxxxxxx> wrote in message
news:1127764694.935366.135340@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> hi, yes but [dx] is not allowed in emu8086. so i figured out the
> solution:

(smile) but for sure it is not allowed. Am I to do all of your
work? :)

> copy dx to bp on which [] is allowed.. then copy [bp] to ax. this is
> working well.

Please note that [bp] will use the stack segment by default
instead of the data segment as you would expect. It just
so happens that in your .COM program, ss = ds.

You could also use direct addressing

mov al,[buffer]

and not have to use a register at all.

> thanks for the help!

You're welcome.
Ben

> Benjamin David Lunt wrote:
>> <spamtrap@xxxxxxxxxx> wrote in message
>> news:1127560389.208499.175090@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> > Hi! I am new to assembly. I am currrently writing a program that opens
>> > a file, reads on character at a time and print each character on the
>> > screen. It prints the '$' character in a seemingly infinite loop. Here
>> > is my code:
>> >
>> > org 100h ;.com memory layout
>> >
>> > mov dx, offset file ;address of file to dx
>> > mov al,0 ;openfile (read-only)
>> > mov ah,3dh
>> > int 21h ;call the interupt
>> > jc terminate ;if error occurs, terminate program
>> > mov bx,ax ;put handler to file in bx
>> >
>> > mov cx,1 ;read one character at a time
>> > print:
>> > mov ah,3fh ;read from the opened file (its handler in bx)
>> > int 21h
>> > jc terminate ;end program if end of file is reached
>> > mov ax,dx ;char is in dl, send to ax for printing (char is in
>> > al)
>>
>> This service does not return the character in DX. This service
>> reads CX bytes to the buffer pointed to by ds:dx, so the character
>> is at ds:[dx] which just so happens to be the first character of
>> FILE below.
>>
>> As for printing '$', I think that dx just may be 0x0124, since the
>> offset of FILE may be 0x0124.
>>
>> As for the infinite loop, the carry is not set at EOF. Check
>> for ax == cx after the service. AX is returned as the amount
>> of bytes actually read. If AX == CX, then EOF was not found
>> upon trying to read a number of bytes. This doesn't mean that
>> the current file posision isn't at the eof, it just means that
>> eof was not encountered when trying to read CX bytes.
>>
>> > mov ah,0eh ;print character
>> > int 10h
>> > jmp print ;repeat if not end of file
>> >
>> > terminate:
>> > ret
>> >
>> > file db "c:\input.txt",0
>> > handle dw ?
>>
>> Ben
>>
>> --
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>>
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>> Some assembly required.
>



.

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