Replacing a unicode character in UTF-8 file using delphi 2010

Question

I am trying to replace character (decimal value 197) in a UTF-8 file with character (decimal value 65)

I can load the file and put it in a string (may not need to do that though)

SS := TStringStream.Create(ParamStr1, TEncoding.UTF8);
SS.LoadFromFile(ParamStr1);
//S:= SS.DataString;
//ShowMessage(S);

However, how do i replace all 197's with a 65, and save it back out as UTF-8?

 SS.SaveToFile(ParamStr2);
 SS.Free;

-------------- EDIT ----------------

reader:= TStreamReader.Create(ParamStr1, TEncoding.UTF8);
 writer:= TStreamWriter.Create(ParamStr2, False, TEncoding.UTF8);

 while not Reader.EndOfStream do
 begin
  S:= reader.ReadLine;
  for I:= 1 to Length(S)  do
  begin
   if Ord(S[I]) = 350 then
   begin
    Delete(S,I,1);
    Insert('A',S,I);
   end;
  end;
  writer.Write(S + #13#10);
 end;

 writer.Free;
 reader.Free;

Answer 1

Decimal 197 is hex C5 , and decimal 65 is hex 41 .

C5 is not a valid UTF-8 octet by itself, but 41 is. So I have to assume you are actually referring to Unicode codepoints U+00C5 LATIN CAPITAL LETTER A WITH RING ABOVE and U+0041 LATIN CAPITAL LETTER A instead.

U+00C5 is encoded in UTF-8 as C3 85 , and U+0041 is encoded as 41 . To do what you are asking, you have to decode the UTF-8, replace the codepoints, then re-encode back to UTF-8. StringReplace() will work just fine for that, eg:

SS := TStringStream.Create('', TEncoding.UTF8);
SS.LoadFromFile(ParamStr1);

S := StringReplace(SS.DataString, 'Å', 'A', [rfReplaceAll]);

SS2 := TStringStream.Create(S, TEncoding.UTF8);
SS2.SaveToFile(ParamStr2);

SS2.Free;
SS.Free;

Or:

reader := TStreamReader.Create(ParamStr1, TEncoding.UTF8);
writer := TStreamWriter.Create(ParamStr2, False, TEncoding.UTF8);

while not Reader.EndOfStream do
begin
  S := reader.ReadLine;
  S := StringReplace(S, 'Å', 'A', [rfReplaceAll]);
  writer.WriteLine(S);
end;

writer.Free;
reader.Free;

Update: based on other comments, it looks like you are not actually interested in Unicode codepoint U+00C5 LATIN CAPITAL LETTER A WITH RING ABOVE , but rather in U+015E LATIN CAPITAL LETTER S WITH CEDILLA instead, which is encoded in UTF-8 as C5 9E . If that is true, then simply replace Å with Ş when calling StringReplace() after the UTF-8 data has been decoded:

S := StringReplace(S, 'Ş', 'A', [rfReplaceAll]);