Hi,
following the advice of howardpc, I repost here my question from the
forum (https://forum.lazarus.freepascal.org/index.php/topic,60287.0.html).
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?
Ciao,
Gilles Marcou
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);
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begin
14.
(...)
15.
flPos:=TListInt64.Create;
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end;
17.
18.
procedure TStreamReader.Close;
19.
begin
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(...)
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FreeAndNil(flPos);
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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
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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);
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var
5.
apos: Int64;
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begin
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apos:=flPos[n-1];//flPos is 0-based and lines are 1-based
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Reset;
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FStream.Seek(apos,soBeginning);
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end;
11.
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