麻烦请教一下，为什么这个代码会出现这种问题
程序代码：data segment
Pgsize dw ?
buf_size db 80
s_buf db ?
buf db 200 dup(?)
cur dw ?
handle dw ?
mess_getname db 0dh,0ah," Please input filename:$"
mess_err1 db 0ah,0dh," Illegal filename! $"
mess_err2 db 0ah,0dh," File not found ! $"
mess-err3 db 0ah,0dh," File read error ! $”
mess-psize db 0ah,0dh," Page Size : $”
crlf db 0ah,0dh,"$"
mess_star db 0ah,0dh,"**************************"
db 0ah,0dh,"$"
data ends
code segrnent
assume ds:data,cs:code
main proc far
start:
push ds
sub ax,ax
push ax
mov ax,data
mov ds,ax
mov PgSize,12 ;Each page 12 lines.
mov cur,200 ;File data buffer is empty.
call getline ; Get file name.
call openf ; open the file , (ax)=0 means no such file
or ax,ax
jnz display
mov dx,offset mess_err2
mov ah,09h
int 21h ;(ax)=0 : no such file.
jmp file_end
display:
mov cx,PgSize
show_page:
call read_block ; read a line from handle to buf
or ax,ax
jnz next2
mov dx,offset mess_err3
mov ah,09h
int 21h ;(ax)=0 : error in read.
jmp file_end
next2:
call show_block ; display a line in buf , (bx) returned o
; means that the file reach its end.
or bx,bx
jz file_end ;(bx)=0: at the end of file.
or cx,cx
jnz show_page ;(cx)<>0; not the last line of a page.
mov dx,offset mess_star
mov ah,09h
int 21h ;At the end of a page，print a line of * .
; the current page has been on screen，and followed by a line of stars.
;the following part get the command from keyboard:
wait-space:
mov ah,1
int 21h
cmp ai," "
jnz psize
jmp display
psize:
cmp al,"p"
jnz wait-space
call change_psize
here:
mov ah,1
int 21h
cmp al," "
jnz here ;stick here to wait for space.
jmp display
file_end:
ret
main endp
;****************************************************************
;****************************************************************
change_psize proc near
push ax
push bx
push cx
push dx
mov dx,offset mess_psize
mov ah ,09h
int 21h ;print the promt line
mov ah,01
int 21h ;get the new num. of page size.
cmp al,0dh
jz illeg
sub al,"0"
mov cl,al
getp:
mov ah,1
int 21h
cmp al,0dh
jz pgot
sub al,"0"
mov dl,al
mov al,cl
mov cl,dl ;exchange al and cl.
mov bl,10
mul bl
add cl,al
jmp getp
pgot:
mov dl,0ah
mov ah,2
int 21h ;output Oah to complete the RETURN.
cmp cx,0
jle illeg
cmp cx,24
jg illeg
mov PgSize,cx ; be sure the new page size in (o..24) region.
illeg:
mov dl,0ah
mov ah,2
int 21h ;output Oah to complete the RETURN.
pop dx
pop cx
pop bx
pop ax
ret
change_psize endp
;****************************************************************
;****************************************************************
openf proc near
push bx
push cx
push dx
mov dx,offset buf
mov al,0
mov ah,3dh
int 21h
mov handle,ax
mov ax,1
jnc ok
mov ax , 0
ok:
pop dx
pop cx
pop bx
ret
openf endp
;****************************************************************
;****************************************************************
getline proc near
push ax
push bx
push cx
push dx
mov dx,offset mess_getname
mov ah,09h
int 21h ; promt user to input file name.
mov dx,offset buf_size
mov ah,0ah
int 21h ; function call of buffer input.
mov dx,offset crlf
mov ah,09h
int 21h ; return.
mov bl,s_buf
mov bh,0
mov [buf+bx],0 ;put 0 into the end of file name
pop dx
pop cx
pop bx
pop ax
ret
getline endp
;****************************************************************
;****************************************************************
read_block proc near
push bx
push cx
push dx
cmp cur,200
jnz back
; if no more chars in buf can be displayed
; then read another 200 chars ;
mov cx,200
mov bx , handle
mov dx , offset buf
mov ah , 3fh
int 21h
mov cur,0
mov ax,1
jnc back
mov cur,200
mov ax ,0
back:
pop dx
pop cx
pop bx
ret
read_block endp
;****************************************************************
;****************************************************************
show_block proc near
push ax
push dx
mov bx,cur
loop1:
cmp bx,200
jl lp
jmp exit ; if buf is empty then return.
lp:
mov dl,buf[bx] ;else show the currnet char.
cmp dl,1ah ; search the file end
jz exit_eof
inc bx
inc cur
mov ah,02
int 21h
cmp dl,0ah
jz exit_ln ;if the char shown is RETURN,
;then exit. A line has been on screen.
jmp loop1
exit_eof:
mov bx,0
exit_ln:
dec cx
exit:
pop dx
pop ax
ret
show_block endp
;****************************************************************
code ends
end start
