find valid drives

 BBS: Inland Empire Archive
Date: 04-19-92 (21:52)             Number: 195
From: BRENT ASHLEY                 Refer#: NONE
  To: ALL                           Recvd: NO  
Subj: find valid drives              Conf: (2) Quik_Bas

I forget who was asking, but here's a routine I came up
with about a year ago to find all available drives on a
system.  It finds network drives, ramdisks - the lot - all
without actually polling the drive, so floppy
considerations are unimportant.  It will, however, tell you
there is a b drive even if it's a phantom drive.  Equipment
byte in BIOS area should help determine whether b actually
exists.

-----
Brent
-----

'
' Drives.BAS - Checks valid drives without accessing them
'
' by Brent Ashley - do as you wish with it.
'
' $INCLUDE: 'QB.BI'
DEFINT A-Z
DECLARE FUNCTION ValidDrv% (DriveLetter$)

PRINT "Valid Drives are - ";
FOR Drive = 65 TO 90 ' ("A" to "Z")
  DrvLtr$ = CHR$(Drive)
  IF ValidDrv(DrvLtr$) THEN PRINT DrvLtr$; ": ";
NEXT

FUNCTION ValidDrv (DriveLetter$)
  STATIC Letter$, Regs AS RegTypeX, DummyFCB AS STRING * 43
  Letter$ = DriveLetter$ + ": "
  Regs.ax = &H2906               ; int 21h svc 29h - parse filename
  Regs.ds = VARSEG(Letter$)      ;
  Regs.si = SADD(Letter$)        ; use sadd for string
  Regs.es = VARSEG(DummyFCB)     ;
  Regs.di = VARPTR(DummyFCB) + 7 ; extended fcb extends back 7 bytes
  InterruptX &H21, Regs, Regs
  ValidDrv = -1                  ; assume true
  IF (Regs.ax AND 255) = 255 THEN ValidDrv =  0 ; parse fails on bad drive
END FUNCTION



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