File Exists fn

[Kurt Schultz]

Hello, folks -

I've had to pick up an old project that I wrote a long time ago.
The app is running under MS-DOS 6.22 and I'm writing the code to compile under PD for DOS, version 3.22.

One of the functions that I wrote is called FileExists. It is to return %False if it cannot fine the file that was passed to it as an argument, and to return %True if it finds the file.
It also attempts to cope with the entire path information provided as an argument, for those situations where the sought file is expected in a subdirectory other than what is currently local.

For some reason, the program does not detect files that it should.

Do any of you have a similar function that I could study?

Kurt Schultz

[Tom Hanlin]

Bound to be one in the PB/DOS examples folder...

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Tom Hanlin
PowerBASIC Staff

[Michael Mattias]

FUNCTION Exists (s AS STRING) AS INTEGER
  FUNCTION = DIR$(S) <> ""
END FUNCTION

[Kurt Schultz]

Hi, Tom -

If so (and it is likely), it would be a simplified version that's not sophisticated enough for what needs to be done in this app.
One of the problems I encountered was in trying to detect files that existed in directories other than the currently-local directory.


Hi, Michael -

If I remember correctly, your approach has problems if it gets a null string as an argument.
This is essentially what my routine does after storing and removing the path from the file name, except that the routine also tests for null input.
If the input is not null, then it tests via the DIR$.

Kurt Schultz

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[Mel Bishop]

If I'm reading your problem right, the following example should
be useful.

path$ = "c:\mystuff\pb35\"
fname$ = "somefile.bas"
te$ = dir$(path$ + fname$,{Attribute))

If te$ <> "" then te$ will only contain the file name being
sought. DIR$ will return only the file name whether you are in
the directory in question or not.

Also, PB/DOS does not support LFN's. It can only digest SFN's.

You might want to check out the ATTRIBUTE option. That will
reduce the number of files returned.


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[Kurt Schultz]

Hi, Mel -

My approach is somewhat inverted compared to yours.

I strip off the drive and directory information, leaving only the filename, then switch to that directory, trigger the DIR$ command, then restore to the directory that was in use before the function was called.

Specifying an attribute code would be redundant.

It seems like I'm getting a null string from the DIR$ fn even if the file exists.

I'm tempted to bypass the DIR$ fn and write it as a DOS call.


Kurt Schultz


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[Michael Mattias]

A lot of old MS-DOS BASIC code was originally created before all BASICs had functions like DIR$, or before those BASIC's handled a PRINT statement via direct screen writes, or before there was automatic string garbage collection, or when machines were like my first PC, a screaming dual-speed 4.77/6.0 Mhz.

Some of those library- and utility-type functions in commercial libraries just do not make sense anymore, as "what they replaced" or "what gap they filled" no longer need replacement or remain gaps.

MCM

[Tom Hanlin]

Why would you assume there would be a problem handling drives or
directories? There is no reason for such a limitation.

See the Exist function in your PB/DOS Examples folder, DOSUNIT.BAS.

Yes, you may need to filter out empty filespecs yourself, if you
expect to pass them.

If you are using LFN filenames (Windows "Long FileName" convention),
you will not be able to pass those directly. Either use the short
version of the name, or try one of the LFN libraries in the Download
section.

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Tom Hanlin
PowerBASIC Staff

[Kurt Schultz]

Hi, Tom -

The assumption about drives and directories is related to a User Configuration issue, not directed at any supposed limitation in the compiler.

Also, the app needs to interface with several other companies' programs, and they hand off the parameters to my program in a variety of ways. Reduction to Drive$ + Directory$ + FileName$ seemed most reasonable for handling all of the potential situations.

LFNs are not at issue, this legacy software predates Win95. Come to think of it, I believe this project was started under PB 2.2 (or maybe some earlier version).

I looked at the DOSUNIT and DIRUNIT stuff earlier today, but had an appointment for some new glasses and couldn't play with the code as much as I wanted to.

I'm tempted to write a DTA monitor to see if things are happening as I think they ought to be happening.

I'll do some more on it tomorrow.


Kurt Schultz


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[This message has been edited by Kurt Schultz (edited June 18, 2003).]

[Kurt Schultz]

Here's the code:

FUNCTION FileExists (FileExistsFileSpec AS STRING) LOCAL PRIVATE
' If the FileExistsFileSpec includes path information, it will be used,
' otherwise, this FUNCTION will search in the current default
' directory. If you include a wild card in the FileExistsFileSpec, any
' matching file name will make this FUNCTION return a logical
' 'True' (non-zero) value.

DIM DirName AS STRING
DIM OldPath AS STRING
DIM OldParam AS STRING
DIM PathPart AS STRING

OldParam = FileExistsFileSpec
DirName = ""
OldPath = ""

' erosive transfer of path info
WHILE INSTR(FileExistsFileSpec, "\")
' while FileExistsFileSpec contains "\" character(s)
' build DirName$
PathPart = EXTRACT$(FileExistsFileSpec, "\") + "\"
DirName = DirName + PathPart
FileExistsFileSpec = LTRIM$(FileExistsFileSpec, PathPart)
FileExistsFileSpec = LTRIM$(FileExistsFileSpec, "\")
WEND

IF LEN(DirName) THEN
OldPath = CURDIR$
CHDIR RTRIM$(DirName, "\")
END IF

IF FileExistsFileSpec = "" THEN
' Error - no filename passed to procedure
FileExists = %False
ELSE
IF DIR$(FileExistsFileSpec) = "" THEN
' Error - File not found
FileExists = %False
ELSE
' Success - File Found
FileExists = %True
END IF
END IF

IF LEN(OldPath) > 0 THEN CHDIR RTRIM$(OldPath, "\")

FileExistsFileSpec = OldParam

END FUNCTION

It's not finding a file that is there.

Kurt Schultz

Yuck, it's trashed my format... ok, hope you can read it
correctly - KAS
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[This message has been edited by Kurt Schultz (edited June 19, 2003).]

[Clay Clear]

Kurt,

Are you familiar with using code written for MASM 6.14 that is
compiled to OBJ files for inclusion in main PB/DOS EXE's? If
you are, I could post my "ExistFile" source code. It autodetects
whether the current environment will support LFN's or not, and then
uses the LFN or the SFN approach, as appropriate. Either that, or
I could boil the OBJ file down to just that function, and e-mail the
compiled file to you.


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[Kurt Schultz]

Hi, Clay -

I can read ASM, although not really well. I almost hate to admit it, but at one point I was actually better with machine code than with ASM. That was before I retired my 8080A machine.

It would be a little tedious, but I could write some inline ASM that would trigger the appropriate DOS interrupt for this situation. I'd probably crib most of it from the Programmer's Problem Solver.

Once again, LFNs are not an issue; the app runs under MS-DOS 6.22 and all subordinate files conform to the 8.3 filename.typ limits.


Kurt Schultz


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[Clay Clear]

Kurt,

The detection of whether or not the current environment supports
LFN's is automatic in my OBJ file's function - there is no need
to alter anything in the code, as, since you say your proggies
will run under plain DOS, then it will detect that, and automatically
use the SFN part of its code. So, your answer was not very, ummm,
informative - would you like for me to post the source code, or
e-mail to you the compiled OBJ file? I love dabbling in ASM, so if
you want, I'll even port the code over to a form that can be compiled
as a PB/DOS UNIT. 'Twould be quite easy to do.


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[Kurt Schultz]

Hi, Clay -

If the ASM source code isn't really long, I suggest you post it in here.

BTW, I appreciate your interest in this matter & your willingness to help.


Kurt Schultz


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[Clay Clear]

Kurt,

The pleasure is mine.

OK, but before I post the code, I am going to convert it to
PB/DOS UNIT format. That way, any "lurkers" will not have to have
the MASM 6.14 compiler handy to use it - I'll post it in such a
way that all anybody has to do is copy-and-paste it, then compile it.
So, it'll take me a while (couple of hours?), as the OBJ file's
source file actually contains a number of different routines, so
I will have to sort it out. And, that's the other reason for converting
it to UNIT form, so I do not post a big bit of spaghetti code. <grin>


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[Kurt Schultz]

Hi, Clay -

If it's "spaghetti code", couldn't you just "Cut-n-PASTA" it?

(sorry, couldn't resist)


Kurt Schultz


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[Clay Clear]

#IF 0
Kurt,

<laugh> Good one! <chuckle>

OK, here's the code:
#ENDIF

$COMPILE UNIT
$DIM ALL

TYPE DTA
    junk1(1 TO 21) AS BYTE
    nAttributes AS BYTE
    junk2 AS DWORD
    nFileSize AS DWORD
    nFileName AS ASCIIZ*13
END TYPE

FUNCTION Test (BYVAL A AS STRING, BYVAL B AS INTEGER) PUBLIC AS INTEGER
    DIM wx AS ASCIIZ*68
    DIM tempdta AS DTA
    wx = A
    ! lea dx, tempdta
    ! mov ah, &H1A
    ! int &H21
    ! xor ch, ch
    ! mov cl, &B00100111
    ! lea dx, wx
    ! mov ax, &H4E00
    ! stc
    ! int &H21
    ! jnc P1A
    ! xor ax, ax
    ! jmp P2A
    P1A:
    ! mov ax, 1
    P2A:
    ! mov bx, B
    ! or bx, bx
    ! jz P3A
    ! xor ax, 1
    P3A:
    ! neg ax
    ! mov FUNCTION, ax
    ! push ss
    ! pop ds
END FUNCTION

#IF 0
Argument 'A' is the path/name of the file whose existence you are
checking for. Argument 'B' tells the function to reverse its
return. If the file does exist, and 'B' is zero, then it returns -1.
If the file does not exist, and 'B' is zero, it returns 0 (zero).
If the file does exist, and 'B' is nonzero, it returns 0. If the file
does not exist, and 'B' is nonzero, it returns -1.

Any questions, etc., feel free to ask!

P.S. This function only includes code that works for 8.3 file names - it
will NOT work with LFN's.
#ENDIF




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[Mike Burgett]

Kurt,

This is what I use to determine if a file exist:


FILE$ = "F:\public\FileName.Dat" 'Path and File name here
x$ = DIR$(file$) 'Look for File

IF x$ = RIGHT$(file$,12) THEN 'Check just the name for match
Indicator = 1 'True
ELSE
Indicator = 0 'False
END IF



Hope this helps.


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Michael Burgett

[Kurt Schultz]

Hi, Mike -

Your name's familiar - FIDO/BBS operator? I think you used to be the
SYSOP on one of the boards I used.

If you're the same guy, then Gene, Lance and Ray would be curious to
know if you're ok & how you're doing.

Regarding the FileExists fn, I've reverted to the simpler way of checking
(because it works), so that I can resume testing the remainder of the
package. I know there was a reason that I went to the more complex fn,
but it's been so long that I cannot remember what the issue was.

I guess if I get back into the mindset I had then, I'll be able to
resume work on it.


Kurt Schultz


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[This message has been edited by Kurt Schultz (edited June 22, 2003).]

[Kurt Schultz]

Hi, Lance -

If you're able to, I'd like for you to try the source code I put
in this thread. I'm curious to know if it fails for you the
same way it fails for me.


Kurt Schultz


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