How operate on TFileStream

Question

Hello recently I replace TextFile with TFileStream. I never use it so I have small problem with it.

• How can I add someting to my file after I assign it to variable?
• How can I read someting form that file?

I need defined line form that file so I was doing something like that:

var linia_klienta:array[0..30] of string;
AssignFile(tempPlik,'klienci.txt');
Reset(tempPlik);
i:=0;
While Not Eof(tempPlik) do
  begin
    Readln(tempPlik,linia_klient[i]);
    inc(i);
  end;
CloseFile(tempPlik);

Then when line two is needed I simply

edit1.text = linia_klienta[1];

Solution 1

If you need to read a text file and access each line, try instead using a TStringList class with this class you can load a file, read the data (accesing each line using a index) and save the data back.

something like this

FText  : TStringList;
i : integer;
begin
 FText := TStringList.Create;
 try
  FText.LoadFromFile('C:\Foo\Foo.txt');

    //read the lines
    for i:=0 to FText.Count-1 do    
     ProcessLine(FText[i]);  //do something   

  //Add additional lines
  FText.Add('Adding a new line to the end');
  FText.Add('Adding a new line to the end');    

  //Save the data back
  FText.SaveToFile('C:\Foo\Foo.txt');

 finally
  FText.Free;
 end;

end;

end;

Solution 2

I newer versions of Delphi you can use TStreamReader / TStreamWriter here is an example of using TStreamReader ... this is only for manipulating text files

var
  SR : TStreamReader;
  line : String;
begin
  SR := TStreamReader.Create('D:\test.txt');
  while not (SR.EndOfStream) do
  begin
    line := SR.ReadLine;
    ShowMessage(line);
  end;
  SR.Free;
 end;

Comments

[Błażej]

That looks nice... wait for it. Can I create new file?

[OnTheFly]

Using TStrings is very memory-inefficient.

[RRUZ]

@Dudi, yes only get rid the line loadfromfile and then add new lines.

[Arnaud Bouchez]

@user539484 TStringList is not bad for normal text files size. In the OP question, it states [0..30] of string which is pretty nothing. In this case, TStringList is just efficient and easy to use.

[Błażej]

@PRUZ Sorry but it is not perfectly clear for me. When I want create new file how it look like?

[Błażej]

I'm using array of string. I need create new file/load from file, add new content to file.

[Conrad Hildebrand]

@Dudi: SaveToFile creates a new file, if it does not yet exist.

[Błażej]

But why when use 'SaveToFile' it overwrite exist content?

[Błażej]

@PRUZ there is any chace to save exist content?

[RRUZ]

Are you trying of append data to this file? btw is RRUZ not PRUZ.

[umlcat]

I also suggest to use the TStringList class to manage several lines instead on a plain array. The problem here is how to read / write all those lines with a text / edit / memo control. The previous TStringList example already shows that.

[OnTheFly]

@Arnaud Bouchez, you have to define "normal" text file size first :-) BTW, OP reads to EOF, so N of lines might be more that just 31 (X < 62G-31 bytes)

[RRUZ]

@Dudi, yes use the delete method passing the index of the line to remove FText.Delete(Index); btw if you have any addional question about this class fell free to ask(start) a new question in S.O.

[Błażej]

I know I should but i figure that out quickly with this