Hello FPC-Pascal,
Tuesday, April 12, 2011, 12:51:17 AM, you wrote:
jgc> So the idea is to open file eg as file of array [1:65536] of char or
jgc> something similar, seek & read to end of file, then go through the last
jgc> array converting to strings by finding crlfs correct? Is this the simplest
jgc> way? If not any outline code?
There is the right way which is a bit complex as there are 3 different
line ending sequences based in the platform. The code get simpler if
you support only one end of line, but as in your case you only need 4
lines and this lines for sure are not too large there is a more simple
way, not very elegant but simple:
function GetLast4Lines(const aFileName: ansistring): ansistring;
var
Lines: TStringList;
FileToRead: TFileStream;
Buffer: ansistring;
ToReadBytes: int64;
i: integer;
begin
//Open the file with fmShareDenyNone, so other process can write in
//the file while I'm reading
FileToRead := TFileStream.Create(aFileName,fmOpenRead or fmShareDenyNone);
//Can I read at least 4096 bytes ?
if FileToRead.Size > 4096 then ToReadBytes := 4096 else ToReadBytes :=
FileToRead.Size;
//Locate read position at 4096 bytes from the end
FileToRead.Position := FileToRead.Size - ToReadBytes;
//Setup buffer to space needed
SetLength (Buffer, ToReadBytes);
//Read the last 4096 or less bytes in Buffer
FileToRead.Read (Buffer[1], ToReadBytes);
//Release the file, not needed anymore.
FileToRead.Free;
//Create a lines array
Lines := TStringList.Create;
//Assign the buffer to the lines array
Lines.Text := Buffer;
//Initialize output to nothing
Result:='';
//Read from lastline-4 to lastline
for i := Lines.Count-1-4 to Lines.Count-1 do
begin
//Add each line to the output
Result := Result + Lines[i] + LineEnding;
end;
//Release lines array
Lines.Free;
//Result now have the last 4 files.
end;
--
Best regards,
José
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