file.asm

这是一些例程

        .MODEL small, pascal, os_dos
        INCLUDE demo.inc
        .CODE

;* ReadCharAttr - Reads character and display attribute at cursor location.
;*
;* Shows:   BIOS Interrupt - 10h, Function 8 (Read Character and Attribute
;*                                at Cursor)
;*
;* Uses:    vconfig - Video configuration structure (initialized
;*          by calling the GetVidConfig procedure)
;*
;* Params:  Attr - Pointer to short integer for display attribute
;*
;* Return:  Short integer with ASCII value of character

ReadCharAttr PROC USES di,
        Attr:PWORD

        mov     ah, 8                   ; Function 8
        mov     bh, vconfig.dpage       ; Current page
        int     10h                     ; Read Character and Attribute
        sub     bh, bh
        mov     bl, ah                  ; BX = attribute
        cbw                             ; AX = character
        LoadPtr es, di, Attr            ; ES:DI = pointer to int
        mov     es:[di], bx             ; Copy attribute
        ret

ReadCharAttr ENDP


;* CopyFile - Copies a file from a specified directory to another. Allows
;* two different copy methods. See the OpenFile, CloseFile, ReadFile, and
;* WriteFile procedures for specific examples on opening, closing, reading
;* from, and writing to files.
;*
;* Shows:   DOS Functions - 3Ch (Create File)
;*                          5Bh (Create New File)
;*          Instruction - clc
;*
;* Params:  Imode  - 0 = Create new target file or overwrite existing file
;*                   1 = Abort and return error code if target file already
;*                       exists (for DOS versions 3.0 and higher only)
;*          Fspec1 - Pointer to ASCIIZ source file specification
;*          Fspec2 - Pointer to ASCIIZ target file specification
;*
;* Return:  Short integer with error code
;*          0 if successful
;*          1 if error

        .DATA
Buffer  BYTE    BUFFERSIZE DUP (?)     ; Buffer for diskette read

        .CODE

CopyFile PROC USES ds si di,
        Imode:WORD,
        Fspec1:PBYTE,
        Fspec2:PBYTE

        LOCAL eof_flag:BYTE

; Open source file for read only

        LoadPtr ds, dx, Fspec1          ; Point DS:DX to source file
        mov     ax, 3D00h               ; AH = function #, AL = access code
        int     21h                     ; Open file (for read only)
        jc      exit
        mov     si, ax                  ; SI = file handle for source

; Open target file according to copy mode

        LoadPtr ds, dx, Fspec2          ; Point DS:DX to target file
        .IF     Imode != 1              ; If Imode (DOS Function) is not 1
        mov     ah, 3Ch                 ; Request Create File
        .ELSE

        ; Check DOS version
        INVOKE  GetVer

        cmp     ax, 300                 ; 3.0 or higher?
        jb      close                   ; No?  Abort with error code
        mov     ah, 5Bh                 ; Request Create New File
        .ENDIF
        sub     cx, cx                  ; Normal attribute for target
        int     21h                     ; DOS function for target file
        jc      close                   ; If open error, abort
        mov     di, ax                  ; DI = file handle for target

; Both files successfully opened. Now read from source and copy to target.

        mov     ax, @data
        mov     ds, ax                  ; DS:DX = buffer. Read/write
        mov     dx, OFFSET Buffer       ;   to and from here.
        mov     eof_flag, 0             ; Initialize end-of-file flag

        .REPEAT
        mov     bx, si                  ; Handle for source file
        mov     cx, BUFFERSIZE          ; CX = number of bytes to read
        mov     ah, 3Fh                 ; Request DOS read
        int     21h                     ; Read from file
        jc      close                   ; If error, exit
        .IF     ax != cx                ; If all bytes not read,
        inc     eof_flag                ;   raise end-of-file flag
        .ENDIF                          ;   to end .REPEAT loop
        mov     bx, di                  ; Handle for target file
        mov     cx, ax                  ; Write number of bytes read
        mov     ah, 40h                 ; Request DOS write
        int     21h                     ; Write from buffer to target file
        jc      close                   ; If error, exit
        .UNTIL  eof_flag != 0           ; Loop to read next block
        clc                             ; Clear CY to indicate success
close:
        pushf                           ; Preserve flags while closing
        INVOKE  CloseFile,              ; Close source file
                si                      ; Handle for source
        INVOKE  CloseFile,              ; Close target file
                di                      ; Handle for target
        sub     ax, ax                  ; Error code = 0
        popf                            ; Recover flags
exit:
        .IF     carry?                  ; If carry set,
        mov     ax, 1                   ;   error code = 1
        .ENDIF
        ret

CopyFile ENDP


;* ChangeDrive - Changes default drive.
;*
;* Shows:   DOS Function - 0Eh (Select Disk)
;*
;* Params:  Drive - Uppercase letter designation for new drive
;*
;* Return:  None

ChangeDrive PROC,
        Drive:WORD

        mov     ah, 0Eh                 ; DOS Function 0Eh
        mov     dx, Drive               ; Drive designation in DL,
        sub     dl, 'A'                 ;   0=A, 1=B, 2=C, etc.
        int     21h                     ; Select Disk
        ret

ChangeDrive ENDP


;* GetCurDrive - Gets designation of current drive.
;*
;* Shows:   DOS Function - 19h (Get Current Disk)
;*          Instruction - cbw
;*
;* Params:  None
;*
;* Return:  Short integer with drive designation
;*          0 = A, 1 = B, 2 = C, etc.

GetCurDrive PROC

        mov     ah, 19h                 ; DOS Function 19h
        int     21h                     ; Get Current Disk
        cbw                             ; AX = drive designation
        ret

GetCurDrive ENDP


;* SetDTA - Sets address for new Disk Transfer Area.
;*
;* Shows:   DOS Function - 1Ah (Set DTA Address)
;*
;* Params:  Dta - Far pointer to new transfer address
;*
;* Return:  None

SetDTA  PROC USES ds,
        Dta:FPBYTE

        lds     dx, [Dta]               ; Point DS:DX to DTA
        mov     ah, 1Ah                 ; DOS Function 1Ah
        int     21h                     ; Set DTA Address
        ret

SetDTA  ENDP


;* GetDTA - Gets address of current Disk Transfer Area.
;*
;* Shows:   DOS Function - 2Fh (Get DTA Address)
;*
;* Params:  Dta - Far pointer to receive transfer address
;*
;* Return:  None

GetDTA  PROC,
        Dta:FPBYTE

        mov     ah, 2Fh                 ; DOS Function 2Fh
        int     21h                     ; Get DTA Address in ES:BX
        mov     ax, es                  ; Save DTA segment
        mov     dx, bx                  ; Save DTA offset
        les     bx, Dta                 ; Now ES:BX points to variable
        mov     es:[bx], dx             ; Copy DTA address to
        mov     es:[bx+2], ax           ;   dta variable
        ret

GetDTA  ENDP


;* CreateFile - Creates file with specified attribute.
;*
;* Shows:   DOS Function - 3Ch (Create File)
;*
;* Params:  Attr - Attribute code:  0 = normal        8 = volume label
;*                                  1 = read only    16 = subdirectory
;*                                  2 = hidden       32 = archive
;*                                  4 = system
;*          Fspec - Pointer to ASCIIZ file specification
;*
;* Return:  Short integer with file handle or -1 for error

CreateFile PROC USES ds,
        Attr:WORD, Fspec:PBYTE

        LoadPtr ds, dx, Fspec           ; Point DS:DX to file spec
        mov     cx, Attr                ; CX = attribute
        mov     ah, 3Ch                 ; AH = function number
        int     21h                     ; Create file
        .IF     carry?
        mov     ax, -1                  ; Set error code
        .ENDIF
        ret

CreateFile ENDP


;* OpenFile - Opens specified file for reading or writing. See the CopyFile
;* procedure for another example of using DOS Function 3Dh to open files.
;*
;* Shows:   DOS Function - 3Dh (Open File)
;*
;* Params:  Access - Access code:  0 = read    1 = write    2 = read/write
;*          Fspec - Pointer to ASCIIZ file specification
;*
;* Return:  Short integer with file handle or -1 for error

OpenFile PROC USES ds,
        Access:WORD, Fspec:PBYTE

        LoadPtr ds, dx, Fspec           ; Point DS:DX to file spec
        mov     ax, Access              ; AL = access code
        mov     ah, 3Dh                 ; AH = function number
        int     21h                     ; Open file
        .IF     carry?
        mov     ax, -1                  ; Set error code
        .ENDIF
        ret

OpenFile ENDP


;* CloseFile - Closes an open file specified by handle. See the CopyFile
;* procedure for another example of using DOS Function 3Eh to close files.
;*
;* Shows:   DOS Function - 3EH (Close File)
;*
;* Params:  Handle - File handle
;*
;* Return:  None

CloseFile PROC,
        Handle:WORD

        mov     bx, Handle              ; BX = file handle
        mov     ah, 3Eh                 ; DOS Function 3Eh
        int     21h                     ; Close file
        ret

CloseFile ENDP


;* ReadFile - Read from open file to specified buffer. See the CopyFile
;* procedure for another example of using DOS Function 3Fh to read files.
;*
;* Shows:   DOS Function - 3Fh (Read File or Device)
;*
;* Params:  Handle - File handle
;*          Len - Number of bytes to read
;*          Pbuff - Pointer to buffer
;*
;* Return:  Short integer with number of bytes read, or 0 if read error

ReadFile PROC USES ds di,
        Handle:WORD, Len:WORD, Pbuff:PBYTE

        LoadPtr ds, dx, Pbuff           ; Point DS:DX to buffer
        mov     di, dx                  ; Keep string offset in DI
        mov     bx, Handle              ; BX = handle
        mov     cx, Len                 ; CX = number of bytes to read
        mov     ah, 3Fh                 ; Request DOS read
        int     21h                     ; Read File
        .IF     carry?
        sub     ax, ax                  ; Set error code
        .ENDIF
        ret
        
ReadFile ENDP


;* WriteFile - Write ASCIIZ string to file. If Handle = 0, the string is
;* written to STDOUT (console). See the CopyFile procedure for another
;* example of using DOS Function 40h to write to files.
;*
;* Shows:   DOS Function - 40h (Write File or Device)
;*          Instructions - inc      dec
;*
;* Params:  Handle - File handle
;*          SPtr - Pointer to ASCIIZ string
;*
;* Return:  Short integer with error code
;*          0 if successful
;*          1 if write error
;*          2 if number of bytes written not equal to string length

WriteFile PROC USES ds di,
        Handle:WORD, Sptr:PBYTE

        LoadPtr es, di, Sptr            ; Point ES:DI to string
        push    di                      ; Hold on to string pointer
        mov     cx, -1                  ; Set CX to maximum
        sub     al, al                  ; AL = 0
        repne   scasb                   ; Scan string for NULL
        pop     dx                      ; Recover string pointer
        dec     di
        sub     di, dx                  ; Get string length (w/o NULL)
        mov     cx, di                  ; Put it into CX
        mov     bx, Handle              ; Load BX with handle
        push    es                      ; Set DS to ES to ensure
        pop     ds                      ;   DS:DX points to string
        mov     ah, 40h                 ; Request DOS write
        int     21h                     ; Write File or Device
        mov     bx, ax                  ; Get number of bytes written
        mov     ax, 0                   ; Set error code, preserve carry
        .IF     carry?                  ; If carry,
        inc     ax                      ;   increment once for write error
        .ENDIF  ; carry
        .IF     bx != cx                ; If bytes not all written,
        inc     ax                      ;   increment twice