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Author Topic: FCL streamex question  (Read 361 times)

marcou

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FCL streamex question
« on: August 16, 2022, 06:48:55 pm »
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][+][-]
  1. TListInt64 = specialize TFPGList<Int64>;
  2. (...)
  3.    TStreamReader = class(TTextReader)
  4.    private
  5.      flPos: TListInt64;
  6.      function ReadPos(Idx: integer): Int64;
  7.      procedure WritePos(Idx: integer; AValue: Int64);
  8. (...)
  9.   public
  10.      property lPos[Idx: integer]: Int64 read ReadPos write WritePos;
  11.  

2. Manage this list
Code: Pascal  [Select][+][-]
  1. function TStreamReader.ReadPos(Idx: integer): Int64;
  2. begin
  3.   Result:=flPos[Idx];
  4. end;
  5.  
  6. procedure TStreamReader.WritePos(Idx: integer; AValue: Int64);
  7. begin
  8.   flPos[idx]:=AValue;
  9. end;
  10.  
  11. constructor TStreamReader.Create(AStream: TStream; ABufferSize: Integer;
  12.   AOwnsStream: Boolean);
  13. begin
  14. (...)
  15.   flPos:=TListInt64.Create;
  16. end;
  17.  
  18. procedure TStreamReader.Close;
  19. begin
  20. (...)
  21.   FreeAndNil(flPos);
  22. end;
  23.  

3. Store line start positions
Code: Pascal  [Select][+][-]
  1. procedure TStreamReader.ReadLine(out AString: string);
  2. var
  3.   VPByte: PByte;
  4.   VPosition, VStrLength, VLength: Integer;
  5. begin
  6.   flPos.Add(FBufferPosition);
  7.  

4. Add a procedure to jump to the desired line
Code: Pascal  [Select][+][-]
  1.   procedure GoToLn(n: integer);
  2. (...)
  3. procedure TStreamReader.GoToLn(n: integer);
  4. var
  5.   apos: Int64;
  6. begin
  7.   apos:=flPos[n-1];//flPos is 0-based and lines are 1-based
  8.   Reset;
  9.   FStream.Seek(apos,soBeginning);
  10. end;
  11.  

howardpc

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Re: FCL streamex question
« Reply #1 on: August 16, 2022, 08:14:18 pm »
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.

marcou

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  • Posts: 10
Re: FCL streamex question
« Reply #2 on: August 17, 2022, 12:09:59 pm »
Thanks for your answer. It is done.


 

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