Using int 21h when ah = 40h no actual output

Question

im trying to use the int 21h ah is 40h but i cant seem to get it to work, when i open my file after the program shuts down it just dont write it in it and theres no output.... any idea why this happenes? i set a side note on the line from which the code bugs out, before it it works perfectly fine.....

;multi-segment executable file template.

.model small
assume cs: code, ds: data 
data segment
player db 0
startText1 db "Hello and welcome to 'Submarines'"
startText2 db "Please enter a game code 5 characters long"
streamRead db 7 dup(0)
fileName db 6 dup (0)
fileOpenError1 db "1 invalid funtion number"
fileOpenError2 db "Game not found, you're the host...."
fileOpenError3 db "3 path not found"
fileOpenError4 db "4 all available handles in use"
fileOpenError5 db "5 access denied"
fileOpenError6 db "6 invalid file handler"
fileOpenSucs db "Succsessfully joined game!"
fileHandler dw ?
readInfo db 405 dup(0)
writeInfo db 405 dup(0)
errors db "error  ",'$' ;;
data ends

.stack

code segment

start:
; set segment registers:
mov ax, data
mov ds, ax
mov es, ax
;;end of setting registers

call xorAll;; clearing all registers

call newScreen ;;setting up a screen for start screen 640x200
call borderOfScreen

;; start screen text:
mov bp, offset startText1
mov bl,0Eh
mov dx,0218h
mov cx,33
call colorTextDisplay 
mov bp, offset startText2
mov bl,0Eh
mov dx,0412h
mov cx,42 
call colorTextDisplay
;; end of start screen text
;; start reading file name and working with playerity 
call xorAll 
mov streamRead,6
mov dx, offset streamRead
mov ah, 0Ah 
int 21h
call preapreFileName
call openFile;; error is handled inside the open file code 
;; players are set and messages have been sent

mov cx,1
mov writeInfo,'1'
call writeBytes; when i use this the first byte of my file doesnt change to 1......
mov cx,1
call readBytes;l;; and this ready method doesnt work, btw there is no error output
mov dl,readInfo
mov ah,2
int 21h 
call closeFile



call terminate




;; procedures:
proc terminate
mov ax, 4c00h
int 21h
ret
endp terminate

proc showErrorMsg
mov ah,09
mov dx, offset errors
int 21h
ret
endp showErrorMsg

proc preapreFileName
mov cx,5
mov bx,offset streamRead 
add bx,2

loopFileName:
    push [bx]
    inc bx
    loop loopFileName

mov cx,5
mov bx,offset fileName
add bx,4
loopFileName1:
    pop ax
    mov [bx],al
    dec bx
    loop loopFileName1
add bx,6 
mov [bx],0  
ret
endp preapreFileName

proc delay
mov dx,0FFFFh 
startBig:
    dec dx
    mov ax,1
    mov ax,2
    mov ax,3
    cmp dx,0
    jne startBig
ret
endp delay


proc newScreen ;;640x200 ;; debugging use 3
mov ax, 000Eh
int 10h
ret
endp newScreen

proc colorTextDisplay;; BL is color as BACK|FORE  BP is offset of text DX is as ROW|COL CX is length of string
mov ah, 13h
mov al ,01
mov bh,0
int 10h
ret
endp colorTextDisplay

proc createFile
mov ah, 13h
mov al, 01
mov bh, 0
mov bl,02h
mov dx, 0615h
int 10h 
call xorAll
mov ah,3Ch
mov cl,2
mov dx, offset fileName
int 21h
mov fileHandler, ax
mov player,1
ret
endp createFile

proc borderOfScreen 
call xorAll
mov bh,0
mov ah,0Ch
mov al,0Eh
mov cx,639
mov dx,199
rightSide:
    int 10h
    dec dx
    cmp dx,0
    jne rightSide
topSide:
    int 10h
    dec cx
    cmp cx,0
    jne topSide
leftSide:
    int 10h
    inc dx
    cmp dx,199
    jne leftSide
botSide:
    int 10h
    inc cx
    cmp cx,639
    jne botSide
mov cx,638
mov dx,198
rightSide1:
    int 10h
    dec dx
    cmp dx,1
    jne rightSide1
topSide1:
    int 10h
    dec cx
    cmp cx,1
    jne topSide1
leftSide1:
    int 10h
    inc dx
    cmp dx,198
    jne leftSide1
botSide1:
    int 10h
    inc cx
    cmp cx,638
    jne botSide1
ret
endp borderOfScreen

proc openFile
call xorAll
mov ah,3Dh
mov al,2
mov dx, offset fileName
int 21h
jc error
mov fileHandler, ax;; if there arent any errors display message:
mov player,2 
mov bp, offset fileOpenSucs
mov ah, 13h
mov cx, 26
mov al, 01
mov bh, 0
mov bl,02h
mov dx, 0615h 
;;end of message display
int 10h
jmp noError1
error:
call displayError
noError1:
ret
endp openFile

proc closeFile
call xorAll
mov ah,10h
mov bx, fileHandler
int 21h
ret
endp closeFile

proc failOpenFile
mov ah, 13h
mov al, 01
mov bh, 0
mov bl,04h
mov dx, 0615h
int 10h 
ret
endp failOpenFile

proc xorAll
xor ax,ax
xor bx,bx
xor cx,cx
xor dx,dx
ret
endp xorAll

proc waitForClick
mov ah,0
int 16h
ret
endp waitForClick

proc readBytes;; cl is bytes to read
call xorAll
mov ah,3Fh
mov bx,fileHandler
mov dx,offset readInfo
int 21h
jc error
ret
endp readBytes

proc writeBytes;; cl is bytes to read
call xorAll
mov ah,40h
mov bx,fileHandler
mov dx,offset writeInfo
int 21h
jc error
ret
endp writeBytes

proc displayError
mov fileHandler, ax

cmp fileHandler,1
    je error1
cmp fileHandler,2
    je error2
cmp fileHandler,3
    je error3
cmp fileHandler,4
    je error5
cmp fileHandler,6
    je error6
error1:
    mov bp, offset fileOpenError1
    mov cx, 24 
    call failOpenFile
    ret
error2:
    mov bp, offset fileOpenError2
    mov cx,35 
    call createFile
    ret
error3:
    mov bp, offset fileOpenError3
    mov cx,16 
    call failOpenFile
    ret
error4:
    mov bp, offset fileOpenError4
    mov cx,30
    call failOpenFile
    ret
error5:
    mov bp, offset fileOpenError5
    mov cx,15 
    call failOpenFile
    ret
error6:
    mov bp, offset fileOpenError6
    mov cx,22 
    call failOpenFile
    ret
endp displayError

;; end of procedures.


code ends

end start ; set entry point and stop the assembler.

Answer 1

This is how you write to the file :

mov cx,1
mov writeInfo,'1'
call writeBytes; when i use this the first byte of my file doesnt change to 1......

Everything looks fine : the string '1' is in the variable writeInfo, and cx is 1, so one character should be written to the file, but this is writeBytes :

proc writeBytes;; cl is bytes to read
call xorAll               ;◄■■ CX IS ZERO !!!
mov ah,40h
mov bx,fileHandler
mov dx,offset writeInfo
int 21h
jc error
ret
endp writeBytes

cx is zero (xor cx,cx), and this is why zero bytes are being written to the file. Just remove call xorAll.

By the way, I found another error :

proc closeFile
call xorAll
mov ah,10h            ;◄■■ THIS VALUE SHOULD BE 3EH.
mov bx, fileHandler
int 21h
ret
endp closeFile