FCL streamex question
lazarus / 64-FPC development

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marcou · 2022-08-16 16:48

Dear community,

recently I wanted to rewind a file to read again a previous line.
After some search I came to the conclusion to modify the TStreamReader
class. Do you think that would be a useful addition? Should it be an a
modification to TStreamReader or a new class?

Below is a sketch of the modifications.

1. Add a list of line start positions in the stream:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TListInt64
= specialize TFPGList<Int64>;(...)   TStreamReader =
class(TTextReader)   private     flPos: TListInt64;     function
ReadPos(Idx: integer): Int64;     procedure WritePos(Idx: integer;
AValue: Int64);(...)   public     property lPos[Idx: integer]: Int64
read ReadPos write WritePos; 
2. Manage this list
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
TStreamReader.ReadPos(Idx: integer): Int64;begin 
Result:=flPos[Idx];end; procedure TStreamReader.WritePos(Idx: integer;
AValue: Int64);begin  flPos[idx]:=AValue;end; constructor
TStreamReader.Create(AStream: TStream; ABufferSize: Integer; 
AOwnsStream: Boolean);begin(...) 
flPos:=TListInt64.Create;end; procedure
TStreamReader.Close;begin(...)  FreeAndNil(flPos);end; 
3. Store line start positions
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TStreamReader.ReadLine(out AString: string);var  VPByte: PByte; 
VPosition, VStrLength, VLength: Integer;begin 
flPos.Add(FBufferPosition); 
4. Add a procedure to jump to the desired line
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i   procedure
GoToLn(n: integer);(...)procedure TStreamReader.GoToLn(n:
integer);var  apos: Int64;begin  apos:=flPos[n-1];//flPos is 0-based
and lines are 1-based  Reset;  FStream.Seek(apos,soBeginning);end;

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howardpc · 2022-08-16 18:14

Michael, who is probably the FCL developer who would assess your
proposal is rarely on this forum.
I suggest you propose your additions on the mailing list, where
Michael often responds.

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marcou · 2022-08-17 10:09

Thanks for your answer. It is done.