Function to check filename validity

[Pete]

Hi all,

What is the best way to check if a certain string can be used as a valid filename?
Basically, I'm looking for a function that receives a string  as argument (passed by reference)
and proceeds as follow:

- checks if the passed string can safely be used as filename
  on the current O/S (or better, on any O/S).
- If yes, then return .T.
 
- If not, then..
  - if passed value is string:
    - if it contains invalid characters attempts to remove them
    - if Len(cString)> MAX_ALLOWED_PATHNAME_LENGTH then
      truncate it to MAX_ALLOWED_PATHNAME_LENGTH,
    - checks again (recursion call) whether the remaining part
      can safely be used as filename and return .T. or .F.

  - if passed value is not a string (i.e.: number, date et.c.):
    - attempts to convert it to string
    - checks again (recursion call) whether the remaining part
      can safely be used as filename and return .T. or .F.

  - Otherwise, return .F.

I don't know if such a function is already available. Any suggestion is welcome.
(Ok, yes, I could try to implement it, myself, but I prefer to be compatible
with the old good rule of not "re-inventing the wheel" etc. :->)

regards,
Pete

[Jayadev U]

Hi,

 

I pass the string to the following ValidExpression function, it substitutes all invalids with an underscore.  You may modify it to suit your purposes.

 

/* code begins */

function validExpression(cInstring)

  local nIter,cThisLetter,nPos := 0

  local cInvalids := "~!@'#$%^&*()-+\.:;-<>"+space(1)

  local nLenString := LEN(cInString)

  local cOutValue := ''

  for nIter = 1 TO nLenString

    cThisLetter := SUBST(cInString,nIter,1)

    IF !(cThisLetter $ cInvalids)

      cOutValue += cThisLetter

    else

      cOutValue += "_"

    ENDIF

  NEXT

  if substr(cOutvalue,-1) = "_"

   cOutvalue := substr(cOutvalue,1,nLenstring-1)

  endif

RETURN cOutValue

/*Code Ends*/

 

HTH,

 

Warm regards,

 

Jayadev

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[Serge Girard]

Hi Jayadev,

I shortened your solution a bit:

FUNCTION valid2Expression(cInstring)
/********************************/
LOCAL nIter
LOCAL cInvalids  := " ~!@'#$%^&*()-+\.:;-<>" 
 
FOR nIter := 1 TO LEN(cInvalids)
   cInstring := STRTRAN(cInstring, SUBSTR(cInvalids, nITER,1) , '_')
NEXT
 
RETURN cInstring

Serge

Op woensdag 29 mei 2019 08:08:43 UTC+2 schreef Pete:

[Jayadev Urath]

Hi Serge,

Nice implementation. Thanks.

However you missed out the space character, it can also be an invalid character in filename.

Warm regards,

Jayadev

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[Alain Aupeix]

Le 29/05/2019 à 09:20, Jayadev Urath a écrit :
> Hi Serge,
>
> Nice implementation. Thanks.
>
> However you missed out the space character, it can also be an invalid
> character in filename.

Surely not, just use "" around the filename to use it with space after get

A+
--
------------------------------------------------------------------------
Alain Aupeix
http://jujuland.pagesperso-orange.fr/
http://pissobi-lacassagne.pagesperso-orange.fr/
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U.buntu 12.04 & Xu.buntu 16.04 | G.ramps 3.4.9-1 | H.arbour 3.2.0dev
(2019-04-11 15:33) | Hw.Gui (2786)
------------------------------------------------------------------------

[Serge Girard]

First char of cInvalids  is a space!

Serge

Op woensdag 29 mei 2019 09:20:21 UTC+2 schreef Jayadev:

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[Pete]

Hi guys,

Thanks for the replies! I took some ideas from your posts.

Just a comment regarding invalid chars:

 - Alain is right that space is valid.

 - Not all chars posted by Jayadev are invalids, although some of them (like f.e.:  ^&%; ) are quite unusual!

However, since I was in a hurry, finally didn't avoid to "invent the wheel".;-)

Below is my implementation.

It'd be useful to get your feedback, particularly bug report, if any.

(In fact, I'm almost sure you'd find some... :-) )

#define MAX_FILENAME_LENGTH 257
FUNCTION IsValidFName( /*@*/ xName, cExt, lSpaceScore, lCheckMaxRelative, cTargetPath, lCheckExists )
    LOCAL cInvalidChars, aTmp
    LOCAL nI, cType

    IF Empty( xName )
        RETURN .F.
    ENDIF

    cType := ValType( xName )

    // acceptable values can be of string, numeric, date or timestamp type
    DO CASE
        CASE cType == "N"
            xName := hb_ntos( xName )
        CASE cType $ "D"
            xName := hb_DtoC( xName )
        CASE cType $ "T"
            xName := hb_TSToStr( xName, .T. )
        OTHERWISE
            IF ! HB_ISSTRING( xName )
                RETURN .F.
            ENDIF
    ENDCASE

    // invalid chars for windows O/S. Linux guys invited to adapt it as needed.
    cInvalidChars := '<>:"/\|?*.'
    FOR nI := 0 TO 31
        cInvalidChars += Chr( nI )
    NEXT
    // prepare to remove invlaid chars
    aTmp := {}
    FOR nI := 1 TO Len( cInvalidChars )
        AAdd( aTmp, "" )
    NEXT
    xName := hb_StrReplace( xName, cInvalidChars, aTmp )
   
    // nothing remained?
    IF Len( xName ) < 1
        RETURN .F.
    ENDIF

    // truncate to valid max length
    xName := Left( xName, MAX_FILENAME_LENGTH )
       
    // transform spaces to underscores, if asked
    IF hb_DefaultValue( lSpaceScore, .F. )
        xName := StrTran( xName, " ", "_" )
    ENDIF

    // now adjust length to be valid when conjuncted to target path
    hb_Default( @cTargetPath, hb_cwd() )
    cTargetPath := hb_DirSepAdd( cTargetPath )

    IF hb_DefaultValue( lCheckMaxRelative, .T. )
        nI := Len( cTargetPath ) + Len( xName )
        ? nI
        IF nI > MAX_FILENAME_LENGTH
            nI := MAX_FILENAME_LENGTH - (nI - MAX_FILENAME_LENGTH)
            xName := Left( xName, nI )
        ENDIF
    ENDIF

    // finally add optional extension and check whether the filename
    // already exists into target path (default current path)
    lCheckExists := ( hb_DefaultValue( lCheckExists, .F. ) .OR. ! Empty( cExt ) )
    IF lCheckExists
        xName := hb_FNameExtSet( xName, hb_DefaultValue( cExt, "" ) )
        IF hb_vfExists( cTargetPath+xName )
            RETURN .F.
        ENDIF
    ENDIF

    RETURN .T.

Any suggestion/correction welcome!

regards,

Pete

[carloskds]

harbour can using regex,

https://stackoverflow.com/questions/11794144/regular-expression-for-valid-filename

FUNCTION ValidaFileName( cRuc, lShowError )

   LOCAL cRegEx := "^[a-zA-Z0-9](?:[a-zA-Z0-9 ._-]*[a-zA-Z0-9])?\.[a-zA-Z0-9_-]+$"

   LOCAL lIsValid := FALSE

   DEFAULT lShowError TO FALSE

#ifdef __XHARBOUR__

   IF ( AllTrim( cRuc ) LIKE cRegEx )

#else

   IF hb_RegexLike( cRegEx, AllTrim( cRuc ) )

#endif

      lIsValid := TRUE

   ENDIF

   IF lShowError .and. !lIsValid

      Alert( "File name not valid!" )

   ENDIF

RETURN lIsValid

[Pete]

 Hi,

Indeed, "regex-es" are extremely effective and helpful.
(sometimes, though, can contribute to mental destabilization
of programmer, due to their "fatal" complexity! :-))

thanks for the code!

regards,
Pete