在Delphi Android中使用TextFile

Question

In my Delphi 10 Seattle app, I am reading a text file (actually an ini file) using TextFile as below:

    SDPath := ClientUtils.GetSharedPath;
    FileName := TPath.Combine(SDPath, 'Client.ini');
    if not MemoVisible then
    begin
      Panel2.Visible := True;
      if FileExists(FileName) then
      begin
        MemoConfig.Lines.Clear;
        AssignFile(T, FileName);
        try
          Reset(T);
          while not Eof(T) do
          begin
            ReadLn(T, text);
            MemoConfig.Lines.Add(text)
          end;
        finally
          CloseFile(T);
        end;
      end

I noticed that the first line contains [Configuration] , 3 additional characters that weren't in the original file. I'm guessing this is from when the client.ini file was deployed from my Windows 7 PC. After I have edited the characters out and saved the file with

      AssignFile(T, FileName);
      try
        Rewrite(T);
        for i := 0 to MemoConfig.Lines.Count -1 do
          WriteLn(T, MemoConfig.Lines[i]);
      finally
         CloseFile(T)
      end;

the file remains correct. Where did the extra characters comes from and what can I do to prevent them from getting into the file?

Answer 1

Those characters are a byte-order mark indicating that your file is encoded as UTF-8. The classic Delphi file-reading functions aren't aware of byte-order marks.

To prevent them from appearing in your file, consult the documentation for the program you used to create the file. You might have the option of excluding the mark explicitly, or you might be able to select a different encoding.

You might wish to avoid further use of the classic text-file functions. You could replace most of your code with a single function call:

MemoConfig.Lines.LoadFromFile(FileName);

That function also offers additional parameters to let you be explicit about what text encoding to use when reading the file. You should always know what text encoding you're using, especially with files that you're in control of like this one.

Answer 2

Those characters are the Unicode UTF-8 byte order markers (EFBBBF hex).

You can prevent them from coming back by properly saving the file from whatever text editor you're using to create it. Save the file as ASCII or ANSI format text.

As far as your code, it's doing a lot more work than it should. You can load the file into your memo much more easily:

SDPath := ClientUtils.GetSharedPath;
FileName := TPath.Combine(SDPath, 'Client.ini');
if not MemoVisible then
begin
  Panel2.Visible := True;
  if FileExists(FileName) then
  begin
    MemoConfig.Lines.Clear;
    MemoConfig.Lines.LoadFormFile(FileName);
  end;
end;

Your code to save the file then becomes the converse:

MemoConfig.Lines.SaveToFile(FileName);