asked on

valid filename

Does anyone have some code that is robust in getting input from an edit component and checking that it is a valid filename?

I currently use a routine that tries to create a file and if that creates an error then i assume it is an invalid filename but this is not the best way to do it as it could be because of another error like disk full, etc.

ntony

try
FileExists(FileName)

foxjax

ASKER

Thanks ntony but i am looking more for a routine that will take what is typed into an edit box and check to see if it is valid - ie: does not contain any invalid characters that are generally not allowed aspart of the filename.

ntony

In OnKeyPress event you coul do this

if not (Key in ['A'..'Z',#8]) then
Key:=#0

with this you alow only letters to be tiped into EditBox

this is only a start!!

foxjax

ASKER

thanks ntony. the main problem is that this allows only letters, and i acknowledge you said it was "only a start" so thanks for the help.

I'm not 100% with delphi as yet myself to be honest but could i use POS to check the filename entered against a list of characters? If so, how would i do this?

ntony

pos(substr,str) return the first position of substr in str

if you want to know all the position you must do something like this

for i:=0 to length(Edit.Text)-1 do begin
if copy(Edit.Text,i,1) in ['A'..'Z'] then begin
//you methods
end;
end;

copy(Edit.Text,i,1) return the character with the position i in the Edit.Text

foxjax

ASKER

Thanks ntony but i cannot get that code to work. The characters i am looking to check for are \/:*?"<>| and if i find a character in the edit.text then i show a message (showmessage).

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ntony

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foxjax

ASKER

Thanks ntony - that seems to have done the trick. the points are yours. thanks for the help.

scrapdog

Try the "IsValidFilename" function below. I didn't test it exhaustively, but let me know how it works for you.

Note that this allows wildcards in the "filename part" of the filename. If you don't want to allow wildcards, just change the declaration of FileChars to

FileChars = AllChars - IllegalChars - IllegalFileChars - Wildcards;

-----------------------------------------------------

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;

type
TForm1 = class(TForm)
Edit1: TEdit;
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.DFM}

// *************************************

function IsValidFilename(Filename :string) :boolean;
type
TCharset = set of char;
const
AllChars = [#0..#255];
Letters = ['a'..'z', 'A'..'Z'];
DriveChars = Letters + [':'];
IllegalChars = ['"', '<', '>', '|'];
IllegalFileChars = ['\', '/'];
WildCards = ['*', '?'];
PathChars = AllChars - IllegalChars - WildCards;
FileChars = AllChars - IllegalChars - IllegalFileChars;

function Illegal(s :string; c :TCharset) :boolean;
var
i :integer;
begin
Result := false;
i := 1;
while (not Result) and (i <= Length(s)) do begin
Result := not (s[i] in c);
Inc(i);
end;
end;

begin

Result := not (Illegal(ExtractFileDrive(FileName), DriveChars))
and not (Illegal(ExtractFilePath(Filename), PathChars))
and not (Illegal(ExtractFileName(Filename), FileChars));

end;

//*********************************

procedure TForm1.Button1Click(Sender: TObject);
begin
if IsValidFilename(Edit1.Text) then
ShowMessage('valid')
else
ShowMessage('invalid');
end;

end.