Simple read/write record .dat file in Delphi

Question

For some reason my OpenID account no longer exists even when I used it yesterday. But anyway.

I need to save record data into a .dat file. I tried a lot of searching

Answer 1

Use streams. Here is a simple demo (just demo - in practice there is no need to reopen file stream every time):

type
  Scores = record
    name: string[50];
    score: integer;
  end;

var rank: array[1..3] of scores;

procedure WriteScores(var Buf; Count: Integer);
var
  Stream: TStream;

begin
  Stream:= TFileStream.Create('test.dat', fmCreate);
  try
    Stream.WriteBuffer(Buf, SizeOf(Scores) * Count);
  finally
    Stream.Free;
  end;
end;

procedure ReadScore(var Buf; Index: Integer);
var
  Stream: TStream;

begin
  Stream:= TFileStream.Create('test.dat', fmOpenRead or fmShareDenyWrite);
  try
    Stream.Position:= Index * SizeOf(Scores);
    Stream.ReadBuffer(Buf, SizeOf(Scores));
  finally
    Stream.Free;
  end;
end;

// write rank[1..3] to test.dat
procedure TForm1.Button1Click(Sender: TObject);
begin
  rank[2].name:= '123';
  WriteScores(rank, Length(Rank));
end;

// read rank[2] from test.dat
procedure TForm1.Button2Click(Sender: TObject);
begin
  rank[2].name:= '';
  ReadScore(rank[2], 2 - Low(rank));
  ShowMessage(rank[2].name);
end;

Answer 2

Look in the help under "blockread" and or "blockwrite". There probably will be an example

Answer 3

You should also take a look at the file of-method.

This is kinda out-dated, but it's a nice way to learn how to work with files.

Since records with dynamic arrays (including ordinary strings) can't be stored to files with this method, unicode strings will not be supported. But string[50] is based on ShortStrings and your record is therefore already non-unicode...

Write to file

var
  i: Integer;
  myFile: File of TScores;
begin
  AssignFile(myFile,'Rank.dat');
  Rewrite(myFile);

  try
    for i := 1 to 3 do
      Write(myFile, Rank[i]);
 finally
   CloseFile(myFile);
 end;
end; 

Read from file

var
  i: Integer;
  Scores: TScores;
  myFile: File of TScores;
begin
  AssignFile(myFile, 'Rank.dat');
  Reset(myFile);

  try
    i := 1;
    while not EOF(myFile) do 
    begin
      Read(myFile, Scores);
      Rank[i] := Scores;      //You will get an error if i is out of the array bounds. I.e. more than 3
      Inc(i);
    end;
  finally
   CloseFile(myFile);
  end;
 end;