Author: Jonas Bilinkevicius

How to read/ write a variable length string from/ to a TFileStream

Answer:

Solve 1:

1   procedure WriteStringToFS(const s: string; const fs: TFileStream);
2   var
3     i: integer;
4   begin
5     i := 0;
6     i := Length(s);
7     if i > 0 then
8       fs.WriteBuffer(s[1], i);
9   end;
10  
11  function ReadStringFromFS(const fs: TFileStream): string;
12  var
13    i: integer;
14    s: string;
15  begin
16    i := 0;
17    s := '';
18    fs.ReadBuffer(i, SizeOf(i));
19    SetLength(s, i);
20    fs.ReadBuffer(s, i);
21    Result := s;
22  end;



Solve 2:

You should be using TWriter and TReader. They make this kind of thing really simple 
to do. Create a stream, writer and reader object at the form level, then 
instantiate them in the OnCreate and destroy them in the OnDestroy event.

23  Stream := TMemoryStream.Create; {Or whatever kind of stream}
24  Writer := TWriter.Create(Stream, 1024);
25  Reader := TReader.Create(Stream, 1024);
26  
27  //Once that's done, try something similar to the following...
28  
29  procedure TForm1.WriteStringToFS(const S: string; Writer: TWriter);
30  begin
31    try
32      Writer.WriteString(S);
33    except
34      raise;
35    end;
36  end;
37  
38  function TForm1.ReadStringFromFS(Reader: TReader): string;
39  begin
40    try
41      Result := Reader.ReadString;
42    except
43      raise;
44    end;
45  end;


No need to save the length of the string because the writer do this automatically. The only caveat is that you need to be sure to create the stream first and to destroy it last.