Delphi: Alternative to using Reset/ReadLn for text file reading

Question

i want to process a text file line by line. In the olden days i loaded the file into a StringList:

slFile := TStringList.Create();
slFile.LoadFr         


        

Answer 1

You can use this sample code:

TTextStream = class(TObject)
      private
        FHost: TStream;
        FOffset,FSize: Integer;
        FBuffer: array[0..1023] of Char;
        FEOF: Boolean;
        function FillBuffer: Boolean;
      protected
        property Host: TStream read FHost;
      public
        constructor Create(AHost: TStream);
        destructor Destroy; override;
        function ReadLn: string; overload;
        function ReadLn(out Data: string): Boolean; overload;
        property EOF: Boolean read FEOF;
        property HostStream: TStream read FHost;
        property Offset: Integer read FOffset write FOffset;
      end;

    { TTextStream }

    constructor TTextStream.Create(AHost: TStream);
    begin
      FHost := AHost;
      FillBuffer;
    end;

    destructor TTextStream.Destroy;
    begin
      FHost.Free;
      inherited Destroy;
    end;

    function TTextStream.FillBuffer: Boolean;
    begin
      FOffset := 0;
      FSize := FHost.Read(FBuffer,SizeOf(FBuffer));
      Result := FSize > 0;
      FEOF := Result;
    end;

    function TTextStream.ReadLn(out Data: string): Boolean;
    var
      Len, Start: Integer;
      EOLChar: Char;
    begin
      Data:='';
      Result:=False;
      repeat
        if FOffset>=FSize then
          if not FillBuffer then
            Exit; // no more data to read from stream -> exit
        Result:=True;
        Start:=FOffset;
        while (FOffset<FSize) and (not (FBuffer[FOffset] in [#13,#10])) do
          Inc(FOffset);
        Len:=FOffset-Start;
        if Len>0 then begin
          SetLength(Data,Length(Data)+Len);
          Move(FBuffer[Start],Data[Succ(Length(Data)-Len)],Len);
        end else
          Data:='';
      until FOffset<>FSize; // EOL char found
      EOLChar:=FBuffer[FOffset];
      Inc(FOffset);
      if (FOffset=FSize) then
        if not FillBuffer then
          Exit;
      if FBuffer[FOffset] in ([#13,#10]-[EOLChar]) then begin
        Inc(FOffset);
        if (FOffset=FSize) then
          FillBuffer;
      end;
    end;

    function TTextStream.ReadLn: string;
    begin
      ReadLn(Result);
    end;

Usage:

procedure ReadFileByLine(Filename: string);
var
  sLine: string;
  tsFile: TTextStream;
begin
  tsFile := TTextStream.Create(TFileStream.Create(Filename, fmOpenRead or    fmShareDenyWrite));
  try
    while tsFile.ReadLn(sLine) do
    begin
      //sLine is your line
    end;
  finally
    tsFile.Free;
  end;
end;