附加在Assembly中的文本文件的末尾

Question

我这里有一个TASM代码，当我再次运行程序时它不附加新字符串。我要感谢us2012帮助我达到这个“状态”。

; This example program creates a file and then writes to it.
.model small
.stack

.data 
CR equ 13
LF equ 10

StartMessage DB "This program creates a file called NEW.TXT"
         DB ,"on the C drive.$"

EndMessage DB CR,LF,"File create OK, look at file to"
       DB ,"be sure.$"

WriteMessage  DB "An error has occurred (WRITING)$"
OpenMessage   DB "An error has occurred (OPENING)$"
CreateMessage DB "An error has occurred (CREATING)$"

WriteMe  DB "HELLO, THIS IS A TEST, HAS IT WORKED?",0
FileName DB "new.txt",0 ; name of file to open 
Handle   DW ?   ; to store file handle 

.code 
START:
mov ax,@data    ; base address of data segment
mov ds,ax   ; put it in ds
mov dx,offset StartMessage 
mov ah,09h 
int 21h 

mov si,offset FileName  ; put offset of filename in dx 
xor cx,cx       ; clear cx - make ordinary file
mov ah,6Ch      ; function 3Ch - create a file
mov al, 0
int 21h         ; call DOS service
mov bx, Handle
xor cx, cx
xor dx, dx
mov ah, 42h
mov al, 02h
int 21h


jc CreateError      ; jump if there is an error



mov si,offset FileName  ; put offset of filename in dx
mov al,2        ; access mode -read and write
mov ah,3Dh      ; function 3Dh - open the file
int 21h         ; call dos service



jc OpenError        ; jump if there is an error



mov Handle,ax       ; save value of handle 
mov bx, Handle
xor cx, cx
xor dx, dx
mov ah, 42h
mov al, 02h
int 21h



mov dx,offset WriteMe   ; address of information to write 
mov bx,Handle       ; file handle for file
mov cx,38       ; 38 bytes to be written
mov ah,40h      ; function 40h - write to file
int 21h         ; call dos service

jc WriteError       ; jump if there is an error
cmp ax,cx       ; was all the data written?
jne WriteError      ; no it wasn't - error!

mov bx,Handle       ; put file handle in bx 
mov ah,3Eh      ; function 3Eh - close a file
int 21h         ; call dos service

mov dx,offset EndMessage 
mov ah,09h 
int 21h 

ReturnToDOS:

mov ax,4C00h        ; terminate program 
int 21h 

WriteError:
mov dx,offset WriteMessage 
jmp EndError

OpenError:
mov dx,offset OpenMessage 
jmp EndError

CreateError:
mov dx,offset CreateMessage 

EndError:
mov ah,09h 
int 21h 
mov ax,4C01h 
int 21h 

END START

如果我使用3Ch，程序可以正常运行，但不会附加到文件的末尾。通过使用6Ch代替3Ch，this表示它不会将现有文件截断为零字节，但每当我运行代码时，创建文件时都会出错（没有文件）被创造了）。请帮我修复代码。非常感谢你！

编辑2：

; This example program creates a file and then writes to it.
.model small
.stack

.data 
CR equ 13
LF equ 10

StartMessage DB "This program creates a file called NEW.TXT"
         DB ,"on the C drive.$"

EndMessage DB CR,LF,"File create OK, look at file to"
       DB ,"be sure.$"

WriteMessage  DB "An error has occurred (WRITING)$"
OpenMessage   DB "An error has occurred (OPENING)$"
CreateMessage DB "An error has occurred (CREATING)$"

WriteMe  DB "HELLO, THIS IS A TEST, HAS IT WORKED?",0
FileName DB "new3.txt",0 ; name of file to open 
Handle   DW ?   ; to store file handle 

.code 
START:
mov ax,@data    ; base address of data segment
mov ds,ax   ; put it in ds
mov dx,offset StartMessage 
mov ah,09h 
int 21h 

mov si, offset FileName     ; put offset of filename in dx 
xor cx,cx       ; clear cx - make ordinary file
mov ah,6Ch      ; function 3Ch - create a file
mov bx, 3
mov dx, 12h
int 21h         ; call DOS service

jc CreateError      ; jump if there is an error

mov ah,3Eh      ; function 3Eh - close a file
int 21h         ; call dos service


mov dx, offset FileName     ; put offset of filename in dx
mov al,2        ; access mode -read and write
mov ah,3Dh      ; function 3Dh - open the file
int 21h         ; call dos service

jc OpenError        ; jump if there is an error

mov Handle,ax       ; save value of handle
mov bx, Handle
xor cx, cx
xor dx, dx
mov ah, 42h
mov al, 02h
int 21h

mov dx,offset WriteMe   ; address of information to write 
mov bx,Handle       ; file handle for file
mov cx,38       ; 38 bytes to be written
mov ah,40h      ; function 40h - write to file
int 21h         ; call dos service

jc WriteError       ; jump if there is an error
cmp ax,cx       ; was all the data written?
jne WriteError      ; no it wasn't - error!

mov bx,Handle       ; put file handle in bx 
mov ah,3Eh      ; function 3Eh - close a file
int 21h         ; call dos service

mov dx,offset EndMessage 
mov ah,09h 
int 21h 

ReturnToDOS:

mov ax,4C00h        ; terminate program 
int 21h 

WriteError:
mov dx,offset WriteMessage 
jmp EndError

OpenError:
mov dx,offset OpenMessage 
jmp EndError

CreateError:
mov dx,offset CreateMessage 

EndError:
mov ah,09h 
int 21h 
mov ax,4C01h 
int 21h 

END START

Answer 1

看看这部分：

mov dx,offset FileName  ; put offset of filename in dx 
xor cx,cx       ; clear cx - make ordinary file
mov ah,6Ch      ; function 3Ch - create a file
mov al, 0
int 21h         ; call DOS service

和the relevant documentation：

AX = 6C00h
BL = open mode as in AL for normal open (see also AH=3Dh)
...
BH = flags
...
CX = create attribute (see #01769).
DL = action if file exists/does not exist (see #01770).
DH = 00h (reserved).
DS:SI -> ASCIZ file name

Return:
CF set on error AX = error code (see #01680 at AH=59h/BX=0000h)
CF clear if successful AX = file handle
CX = status (see #01768) 

该函数希望si而不是dx具有文件名的偏移量。

您未设置bx。

您未设置dx。

您不会检查错误。

您不保存文件句柄。

看看这部分：

mov bx, Handle
xor cx, cx
xor dx, dx
mov ah, 42h
mov al, 02h
int 21h

此时

Handle未初始化，因为您从未将句柄保存到此变量中。

现在，在这里：

mov dx,offset FileName  ; put offset of filename in dx
mov al,2        ; access mode -read and write
mov ah,3Dh      ; function 3Dh - open the file
int 21h         ; call dos service

您正在尝试再次打开打开的文件。你需要在打开之前关闭它。或者，如果你有句柄，只需继续使用该文件，不要关闭并重新打开它。