deletion of binary files

[War Robe]

hi everybody,

I've got a computing project to do and so I'm working on a database. Now the problem is that I don't know (neither can't find) how to delete binary files (within the program) that were created in the program.

Can anyone provide me with a sample code if possible pls? I would really appreciate it!

(Oh and as regards Validations [example: checking whether no numbers have been inserted in the 'name' field], any help on those pls aswell! But primarily the deletion of binary files is my major problem)

Thankyou so much in advance,
War Robe

[jdarling]

Deleteion of any file is simply:

if FlieExists(FileName) then
  DeleteFile(FileName);

As for validation, you can achieve it on two levels. For example if your using a standard Edit control (TEdit) then in its OnKeyPress event you can place code to trap and kill invalid characters:

procedure NameKeyPress(Sender:TObject; var Key:Char);
begin
  if not (Key in ['A'..'Z','a'..'z']) then // check for anything but a-z
    Key := #0; // This kills the key stroke
end;

Take a read through the Delphi help files, and on some basic UI tutorials. Theirs lots of infomraiton out their on this type of stuff. A good resource is Tamaracka.com

[War Robe]

Thanks so much for ur help jdarling. Regarding the 'file exists' I thought it could only be used in text files. But if it works on binary files, where should I put the coding lines pls? At the begining before creating the file?

Cos I need to do an option that if the user selects it, then he types in the file name to be deleted and so it gets deleted.

Thanks alot,
War Robe

[jdarling]

Thanks so much for ur help jdarling. Regarding the 'file exists' I thought it could only be used in text files. But if it works on binary files, where should I put the coding lines pls? At the begining before creating the file?

Cos I need to do an option that if the user selects it, then he types in the file name to be deleted and so it gets deleted.

Thanks alot,
War Robe

Well you would place the code where it would seem most appropriate according to your needs. For example if your wanting to delete an existing file before you create or download the new version then you would place the if exists and delete before you create or download.

So for example if you have the following code:

procedure MyCreateNewFile;
  if SaveDialog1.Execute then
    begin
      // Your code here to create
    end;
end;

Then you might modify it something to this effect:

procedure MyCreateNewFile;
  if SaveDialog1.Execute then
    begin
      if FileExists(SaveDialog1.FileName) then
        DeleteFile(SaveDialog1.FileName);
      // Your code here to create
    end;
end;

[War Robe]

But is

DeleteFile

a built in code? Like the

FileExists

? Beacuse it gives me an 'unknown identifier' error.

Thanks for the rest,
War Robe

[JSoftware]

deletefile is a procedure in the windows api
fileexists is a function from the sysutils unit

you need to include both in your uses clause(eg. "uses sysutils, windows;")

Regards,
Jeppe

[Robert Kosek]

War Robe, if you are using the TFileStream object you can overwrite files easier than these workarounds.

[michalis]

deletefile is a procedure in the windows api

Actually, DeleteFile is also declared in SysUtils unit, al least for FPC and Kylix 3 (so probably also for Delphi >= 6). For portability it's better to not use the version in Windows unit.

So (assuming you use FPC or newer version of Delphi) it should be enough for you to add SysUtils unit to your uses clause.

[JSoftware]

oh ofcourse ops:

i would use the sysutils version of deletefile

you don't need the windows unit included...

[War Robe]

Thanks alot for the info! Although I can't fin a website where I can download the unit (since I don't have one in the units folder).

Any suggestions pls?