Mega Code Archive
Read a certain line number from a text file
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Title: Read a certain line number from a text file
function GrabLine(const AFileName: string; ALine: Integer): string;
var
fs: TFileStream;
buf: packed array[0..4095] of Char;
bufRead: Integer;
bufPos: PChar;
lineStart: PChar;
tmp: string;
begin
fs := TFileStream.Create(AFileName, fmOpenRead);
try
Dec(ALine);
bufRead := 0;
bufPos := nil;
{ read the first line specially }
if ALine = 0 then
begin
bufRead := fs.Read(buf, SizeOf(buf));
if bufRead = 0 then
raise Exception.Create('Line not found');
bufPos := buf;
end else
while ALine 0 do
begin
{ read in a buffer }
bufRead := fs.Read(buf, SizeOf(buf));
if bufRead = 0 then
raise Exception.Create('Line not found');
bufPos := buf;
while (bufRead 0) and (ALine 0) do
begin
if bufPos^ = #10 then
Dec(ALine);
Inc(bufPos);
Dec(bufRead);
end;
end;
{ Found the beginning of the line at bufPos... scan for end.
2 cases:
1) we'll find it before the end of this buffer
2) it'll go beyond this buffer and into n more buffers }
lineStart := bufPos;
while (bufRead 0) and (bufPos^ #10) do
begin
Inc(bufPos);
Dec(bufRead);
end;
{ if bufRead is positive, we'll have found the end and we can leave. }
SetString(Result, lineStart, bufPos - lineStart);
{ determine if there are more buffers to process }
while bufRead = 0 do
begin
bufRead := fs.Read(buf, SizeOf(buf));
lineStart := buf;
bufPos := buf;
while (bufRead 0) and (bufPos^ #10) do
begin
Inc(bufPos);
Dec(bufRead);
end;
SetString(tmp, lineStart, bufPos - lineStart);
Result := Result + tmp;
end;
finally
fs.Free;
end;
end;
function GrabLine2(const s: string; ALine: Integer): string;
var
sl: TStringList;
begin
sl := TStringList.Create;
try
sl.LoadFromFile(s);
Result := sl[ALine - 1]; // index off by one
finally
sl.Free;
end;
end;
Example usage:
GrabLine(filename, 4);
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