Open Existing File

QuickBasic

---

' DOS 2+ - OPEN - OPEN EXISTING FILE

'$INCLUDE: 'qb.bi'

DIM filename AS STRING
DIM Inregs  AS RegTypeX
DIM outregs AS RegTypeX

' need to exist
filename = "C:\INT\123.txt" + CHR$(0)

Inregs.DS = VARSEG(filename)
Inregs.DX = SADD(filename)

' DOS interrupt with sub-function &H3D

' AH - &H3D
' AL - access and sharing modes
'  2-0 access mode: 000 read only
'                   001 write only
'                   010 read/write
'  3 reserved (0)
'  6-4 sharing mode (DOS 3.0+): 000 compatibility mode
'                               001 "DENYALL" prohibit both read and write access by others
'                               010 "DENYWRITE" prohibit write access by others
'                               011 "DENYREAD" prohibit read access by others
'                               100 "DENYNONE" allow full access by others. 111 network FCB (only available during server call)
'  7 inheritance. If set, file is private to current process and will not be inherited by child processes

Inregs.AX = &H3D00 + AL

CALL INTERRUPTX(&H21, Inregs, outregs)

IF outregs.FLAGS AND 1 THEN
   PRINT "Error opening >> " + file$
   ' PRINT "The file was not found"
   Inregs.AX = &H5900
   Inregs.bx = Inregs.bx AND &HFF
   CALL INTERRUPTX(&H21, Inregs, outregs)
   PRINT "This is the error number:"; outregs.AX
   BEEP: END
END IF

' Returns filehandle in AX

DIM filehandle AS INTEGER
filehandle = outregs.AX

PRINT "FileHandle:"; STR$(filehandle)