I want to achieve a very very basic task in Delphi: to save a string to disk and load it back. It seems trivial but I had problems doing this TWICE since I upgraded to IOUti
Then the ReadAFile function should automagically detect the encoding and correctly read the string back.
This is not possible. There exists files that are well-formed if interpreted as any text encoding. For instance see The Notepad file encoding problem, redux.
This means that your goals are unattainable and that you need to change them.
My advice is to do the following:
A text editor that does not understand UTF-8 is not worth supporting. If you feel inclined, include a UTF-8 BOM when you create the file. Use TEncoding.UTF8.GetBytes
and TEncoding.UTF8.GetString
to encode and decode.
Code based on David's suggestions:
{--------------------------------------------------------------------------------------------------
READ/WRITE UNICODE
--------------------------------------------------------------------------------------------------}
procedure WriteToFile(CONST FileName: string; CONST aString: String; CONST WriteOp: WriteOperation= woOverwrite; WritePreamble: Boolean= FALSE); { Write Unicode strings to a UTF8 file. It can also write a preamble }
VAR
Stream: TFileStream;
Preamble: TBytes;
sUTF8: RawByteString;
aMode: Integer;
begin
ForceDirectories(ExtractFilePath(FileName));
if (WriteOp= woAppend) AND FileExists(FileName)
then aMode := fmOpenReadWrite
else aMode := fmCreate;
Stream := TFileStream.Create(filename, aMode, fmShareDenyWrite); { Allow read during our writes }
TRY
sUTF8 := Utf8Encode(aString); { UTF16 to UTF8 encoding conversion. It will convert UnicodeString to WideString }
if (aMode = fmCreate) AND WritePreamble then
begin
preamble := TEncoding.UTF8.GetPreamble;
Stream.WriteBuffer( PAnsiChar(preamble)^, Length(preamble));
end;
if aMode = fmOpenReadWrite
then Stream.Position:= Stream.Size; { Go to the end }
Stream.WriteBuffer( PAnsiChar(sUTF8)^, Length(sUTF8) );
FINALLY
FreeAndNil(Stream);
END;
end;
procedure WriteToFile (CONST FileName: string; CONST aString: AnsiString; CONST WriteOp: WriteOperation);
begin
WriteToFile(FileName, String(aString), WriteOp, FALSE);
end;
function ReadFile(CONST FileName: string): String; {Tries to autodetermine the file type (ANSI, UTF8, UTF16, etc). Works with UNC paths }
begin
Result:= System.IOUtils.TFile.ReadAllText(FileName);
end;
The Inifiles unit should support unicode. At least according to this answer: How do I read a UTF8 encoded INI file?
Inifiles are quite commonly used to store strings, integers, booleans and even stringlists.
procedure TConfig.ReadValues();
var
appINI: TIniFile;
begin
appINI := TIniFile.Create(ChangeFileExt(Application.ExeName,'.ini'));
try
FMainScreen_Top := appINI.ReadInteger('Options', 'MainScreen_Top', -1);
FMainScreen_Left := appINI.ReadInteger('Options', 'MainScreen_Left', -1);
FUserName := appINI.ReadString('Login', 'UserName', '');
FDevMode := appINI.ReadBool('Globals', 'DevMode', False);
finally
appINI.Free;
end;
end;
procedure TConfig.WriteValues(OnlyWriteAnalyzer: Boolean);
var
appINI: TIniFile;
begin
appINI := TIniFile.Create(ChangeFileExt(Application.ExeName,'.ini'));
try
appINI.WriteInteger('Options', 'MainScreen_Top', FMainScreen_Top);
appINI.WriteInteger('Options', 'MainScreen_Left', FMainScreen_Left);
appINI.WriteString('Login', 'UserName', FUserName);
appINI.WriteBool('Globals', 'DevMode', FDevMode);
finally
appINI.Free;
end;
end;
Also see the embarcadero documentation on inifiles: http://docwiki.embarcadero.com/Libraries/Seattle/en/System.IniFiles.TIniFile
Just use TStringList, until size of file < ~50-100Mb (it depends on CPU speed):
procedure ReadTextFromFile(const AFileName: string; SL: TStringList);
begin
SL.Clear;
SL.DefaultEncoding:=TEncoding.ANSI; // we know, that old files has this encoding
SL.LoadFromFile(AFileName, nil); // let TStringList detect real encoding.
// if not - it just use DefaultEncoding.
end;
procedure WriteTextToFile(const AFileName: string; const TextToWrite: string);
var
SL: TStringList;
begin
SL:=TStringList.Create;
try
ReadTextFromFile(AFileName, SL); // read all file with encoding detection
SL.Add(TextToWrite);
SL.SaveToFile(AFileName, TEncoding.UTF8); // write file with new encoding.
// DO NOT SET SL.WriteBOM to False!!!
finally
SL.Free;
end;
end;