Introduction MTB Statements File System Compiler Applications Reference Guide Index

Open DOS File

Syntax: DOSFC(AX-value, CX-value, file-name) EXCP=statement-label
Entry: 
  AX-value = "@3D00@"         (read only)
  CX-value = "@0000@"

  (or)

  AX-value = "@3D42@"         (read/write)
  CX-value = "@0000@"
Return: 
  If the function call is successful, the AX field will contain the
  file's handle.

  If an exception occurs, byte 2 of the AX field will contain the
  DOS error code (in hex).
Discussion: The DOSFC function call can be used to open a DOS file.

For read-only purposes, the function requires that the AX-value be set to "@3D00@" and the CX-value be set to null.

For read/write purposes, the function requires that the AX-value be set to "@3D42@" and the CX-value be set to null.

After the function is executed, the file will be open and the AX register will contain the file's handle. As noted earlier, it is the responsibility of the programmer to ensure that any file handles opened are closed upon completion of the desired function. Failure to comply will result in degradation of system performance and possible system hangs.

Example: 
  ! S SFOPEN,DSK
  ! O FOPEN,DSK
  ! L T00,E
  ! R QMONITOR
  !
  !==========  OPEN DOS FILE HANDLE  =============================
  !
  LENGTH 2 & LOCAL AX$,BX$,CX$,DX$        ! Define registers
             LOCAL FILEHANDLE$            ! Define file handle
  LENGTH 64 & LOCAL FILENAME$             ! Define file name
  !
  LENGTH  3 & LOCAL DOSCODE$              ! Define DOS error code
  LENGTH 37 & LOCAL DOSMESSAGE$           ! Define DOS message
  !
  100 FORMAT (ET)                         ! Screen format
  !
  1000 FORMAT DOSMESSAGE$                 ! File input format
  !
  CLEAR                                   ! Initialize variables
  PRINT (0,100)                           ! Set typewriter mode
  !
  PRINT (0) "ENTER FILENAME TO OPEN:"     ! Display prompt
  INPUT (0) FILENAME$                     ! Enter file name
  IF FILENAME$ = "" THEN RUN "QMONITOR"   ! If null, then stop
  FILENAME$ = FILENAME$ + "@00@"          ! Add null byte to name
  !
  AX$ = "@3D42@"                          ! Set AX to "OPEN FILE"
  CX$ = "@0000@"                          ! Set CX to null
  !
  DOSFC(AX$,CX$,FILENAME$) EXCP=BRANCH1   ! Perform DOSFC call
  !
  FILEHANDLE$ = AX$                       ! Save file handle
  !
  PRINT (0) FILENAME$;" OPENED SUCCESSFULLY."
  PRINT (0) "PRESS ENTER TO CLOSE THE FILE."
  INPUT (0) ""
  !
  AX$ = "@3E00@"                          ! Set AX to "CLOSE FILE"
  BX$ = FILEHANDLE$                       ! Set BX to file handle
  CX$ = "@0000@"                          ! Set CX to null
  DX$ = "@0000@"                          ! Set DX to null
  !
  DOSMS(AX$,BX$,CX$,DX$) EXCP=BRANCH2     ! Perform DOSMS call
  !
  PRINT (0) FILENAME$;" CLOSED SUCCESSFULLY."
  PRINT (0) "PRESS ENTER TO STOP."
  INPUT (0) ""
  RUN "QMONITOR"
  !
  BRANCH1:                                ! Exception routine 1
  PRINT (0) "FILE NOT OPENED."            ! Display message
  OPEN (1) "QERCOMET"                     ! Open error file
  DOSCODE$ = "D" + HEXASC(SUB(AX$,2,1))   ! Construct key to file
  READ (1,1000) KEY=DOSCODE$              ! Read error record
  PRINT (0) "DOS error code: ";DOSCODE$   ! Display DOS error code
  PRINT (0) DOSMESSAGE$                   ! Display error message
  INPUT (0) ""                            ! Hold
  CLOSE (1)                               ! Close error file
  RUN "QMONITOR"                          ! Exit
  !
  BRANCH2:                                ! Exception routine 2
  PRINT (0) "FILE NOT CLOSED."            ! Display message
  OPEN (1) "QERCOMET"                     ! Open error file
  DOSCODE$ = "D" + HEXASC(SUB(AX$,2,1))   ! Construct key to file
  READ (1,1000) KEY=DOSCODE$              ! Read error record
  PRINT (0) "DOS error code: ";DOSCODE$   ! Display DOS error code
  PRINT (0) DOSMESSAGE$                   ! Display error message
  INPUT (0) ""                            ! Hold
  CLOSE (1) & RUN "QMONITOR"              ! Close error file/exit
  END

DOS function calls/pseudo calls