My asm code is writing garbage bytes when I use int 21h function
I did a search on Stack Overflow and I didn't find anything similar to my problem. My problem is this: I have a code that opens a file and writes a message at the end. When I use int 21h to write to a file for the first time, it writes well if the file is empty, but if the file has content, the program adds a lot of garbage bytes (characters like 畂 or other Japanese or Chinese characters) to the end.
I have verified that the program does not write more bytes than the message length. Please help me. Here's my source code:
.model tiny
.code
main:
call delta
delta:
pop bp
sub bp, offset delta
mov ax, @code ;Get the address of code segment and store it in ax
mov ds, ax ;Put that value in Data segment pointer.
;Now, we can reference any data stored in the code segment
;without fail.
;Subroutines
open:
mov ax, 3D02H ;Opens a file
lea dx, [bp+filename];Filename
int 21h ;Call DOS interrupt
mov handle, ax ;Save the handle in variable
move_pointer_to_end:
mov bx, handle
mov ax,4202h ; Move file pointer
xor cx,cx ; to end of file
cwd ; xor dx,dx
int 21h
write:
mov ax, 4000H
mov bx, handle
lea dx, [bp+sign]
mov cx, 16
int 21H
exit:
mov ah,4Ch ;Terminate process
mov al,0 ;Return code
int 21h
datazone:
handle dw ?
filename db 'C:\A.txt', 0
sign db 'Bush was here!!', 0
end main
Please help me!
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This is because the file you are adding data to is unicode encoded. If you write the file from Notepad or another text editor and save it, you need to choose ANSI as the encoding. Then, if you list your program in an ANSI encoded text file, it should add the line specified with the expected result.
Unicode allocates two bytes for each character, so in a hex editor you can see s.o.m.e.t.h.i.n.g. .l.i.k.e. .t.h.i.s.
, not something like this
what you might expect for ANSI or UTF-8.
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