Weird problem! In asm.

[g_gili]

Hi. This is another homwork
I have to do in Newtwide Assembler (nasm) to open a file and count the dots "." in that file and write in the output(on the screen; the number of dots)
So I writed that but it doesn't work... gives me a weird output....
I tried to debug it in TD.exe(Turbo debugger(pascal)) and works fine(the output is what I expect). But if I run the exe file it gives me a wrong output. So what coud be weong??? Manny thanks

ection .code


..start:						  
  mov   ax, data
  mov   ds, ax				    ; data and stack 
  mov   ax, stack
  mov   ss, ax
  mov   sp, stacktop
  jmp   main

ReadString: ;read a string
  xor bx,bx
.read:
  mov ah,0x01
  INT 0x021
  cmp al,0Dh	;if enter end reading
  je end_read
  mov [si+bx],al 
  inc bx
  jmp .read
end_read:
  mov [si+bx],byte 0 ;null termination 
  inc bx
  mov [si+bx],byte '$';string end
retn

write:  ;write something must placed in dx->a string with '$'-char at  
 mov ah,0x09
 INT 0x021
retn
 
error_handling:
 push ax
 mov dx,msg_error
 call write
 xor ax,ax
 INT 0x016
 pop ax
 mov ax, 0x4C00			    ;end file was an error
 int 0x21

ReadChar:					   ;read the caracter from the file

open_file:
  mov ah,3dh				  ;open file
  mov al,0
  mov dx,file_name
 int 0x021
 
  jc error_handling 		   ;if problems then error
  
  mov [handle],ax
  mov bx,[handle]			  ;file handler
  
.read:
   xor dx,dx
   mov ah,3fh				   ;file reading
   mov cx,1    				   ;we read one byte
   int 0x21
 
  cmp ax,cx				    ;if ax=cx then read ok
  je .ok
  cmp ax,0    				  ;if ax=0 then end reading
  je .end_read
  cmp ax,cx					 ;if ax<cx then error
  jb error_handling
  
.ok:  	 
  mov si,dx	
  mov dx,[si]					 ;we put in dx the data(the caracter)
  
  call .count 		;we count the dots(calling the ".count procedure"
  jmp .read
.end_read:

  mov ah,3eH				 ;close the file
  mov bx,[handle]
  int 0x21
retn

.count:
 cmp dl,'.' 
 je .dot
 jmp .count_end
.dot:
 mov ax,[dots]
 add ax,1
 mov [dots],ax
jmp .count_end

.count_end:

retn

WriteInt:  				 ;write out an integer
 mov cx,10
 mov ax,bx
.convert:
 xor dx,dx
 div cx   
 push ax
 mov ah,0x02  
 add dl,48				 ;write's out the number
 INT 0x21
 pop ax
 cmp ax,0   
je .end_w
jmp .convert
 .end_w:
 retn
 
main:
  mov si,file_name	
  call ReadString
  mov dx,file_name	
  call ReadChar
  mov dx,_dots	
  call write
  mov bx,[dots]
  call WriteInt

  mov   ax, 0x4C00			    ; end program
  int   0x021

section .data 				    ; data segment
 msg_error db "An error has occured$"
 _dots db "dots number:$"
  resb 2

section .bss   				  
file_name resb 100
handle resb 2
dots resb 2

section .stack stack			  ; stack segment (4 KB)
  space  resb 4096
stacktop:

[rxbagain]

With my testing on your code, The bug appears to be at the time reading the a character from the file. You set the destination (DX) at 0 (DS:0) which overwrites some of the code sections (in my testing).

You should allocate a variable to place the character read, not just setting it to 0

...

.read:
   mov dx,char_read
   mov ah,3fh
   mov cx,1
   int 0x21
 
   cmp ax,cx
   je .ok
   cmp ax,0
   je .end_read
   cmp ax,cx
   jb error_handling
  
.ok:  	 
   ;mov si,dx	--- remove this line
   mov dx,[char_read]

   call .count
   jmp .read
.end_read:

   ...

section .bss
   file_name resb 100
   handle resb 2
   dots resb 2
   char_read resb 1

...

And for outputing word values, look at THIS POST.

Hope it will help you

[g_gili]

Thanks a lot Now works!