Category : BASIC Source Code
Archive   : BAS_INT1.ZIP
Filename : DIR$.BAS

'=========================================================================
'DIR.BAS by Dave Cleary
'
'One of the most useful additions to BASIC 7 PDS is the DIR$ function.
'This function allows you to read a directory of filenames. It also
'allows you to check the existence of a file by doing the following:
'
' IF LEN(DIR$("COMMAND.COM")) THEN
' PRINT "File Found"
' ELSE
' PRINT "File not found"
' END IF
'
'Now QuickBASIC 4.X users can have this useful function for their
'programs.
'
'Calling DIR$ with a FileSpec$ returns the the name of the FIRST
'matching file name. Subsequent calls with a null FileSpec$ return the
'NEXT matching file name. If a null string is returned, then no more
'matching files were found. FileSpec$ can contain both a drive and a
'path plus DOS wildcards. Special care should be taken when using
'this on floppy drives because there is no check to see if the drive
'is ready.
'========================================================================
'Main()
DEFINT A-Z

DECLARE FUNCTION DIR$ (FileSpec$)

'$INCLUDE: 'QB.BI'

'----- Some constants that DIR$ uses
CONST DOS = &H21
CONST SetDTA = &H1A00, FindFirst = &H4E00, FindNext = &H4F00

'--------------------------------------------------------------------
'This shows how to call DIR$ to find all matching files

'CLS
'FileSpec$ = "C:\QB\SOURCE\*.BAS"
'Found$ = DIR$(FileSpec$)
'DO WHILE LEN(Found$)
' PRINT Found$
' Found$ = DIR$("")
'LOOP

'--------------------------------------------------------------------

FUNCTION DIR$ (FileSpec$) STATIC

DIM DTA AS STRING * 44, Regs AS RegTypeX
Null$ = CHR$(0)

'----- Set up our own DTA so we don't destroy COMMAND$
Regs.AX = SetDTA 'Set DTA function
Regs.DX = VARPTR(DTA) 'DS:DX points to our DTA
Regs.DS = -1 'Use current value for DS
InterruptX DOS, Regs, Regs 'Do the interrupt

'----- Check to see if this is First or Next
IF LEN(FileSpec$) THEN 'FileSpec$ isn't null, so
'FindFirst
FileSpecZ$ = FileSpec$ + Null$ 'Make FileSpec$ into an ASCIIZ
'string
Regs.AX = FindFirst 'Perform a FindFirst
Regs.CX = 0 'Only look for normal files
Regs.DX = SADD(FileSpecZ$) 'DS:DX points to ASCIIZ file
Regs.DS = -1 'Use current DS
ELSE 'We have a null FileSpec$,
Regs.AX = FindNext 'so FindNext
END IF

InterruptX DOS, Regs, Regs 'Do the interrupt

'----- Return file name or null
IF Regs.Flags AND 1 THEN 'No files found
DIR$ = "" 'Return null string
ELSE
Null = INSTR(31, DTA, Null$) 'Get the filename found
DIR$ = MID$(DTA, 31, Null - 30) 'It's an ASCIIZ string starting
END IF 'at offset 30 of the DTA

END FUNCTION