Question

my problem is as follows:

WideCompareStr(FName,'')<>0

returns false even with FName set to ”.

WideCompareStr(trim(FName),'')<>0

returns the desired result. Why do I have to trim an empty string (”) for a comparison with another empty sting to get the correct result?

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EDIT:

to clear things up:
I had the following Code to test wether a widestring-variable is the empty string or not.

function TSybVerwandlung.isEmpty: Boolean;
var
  I : Integer;
begin
  Result:=true;
  if WideCompareStr(FName,'')<>0 then Result:=false
  else if WideCompareStr(FInfo,'')<>0 then Result:=false
  else
  begin
    //additional tests
  end;
end;

This function returned true even with FName set to ” (I checked it in the debugger). After inserting trim(FName) and trim(FInfo) instead of the variables, it returned the desired result.

Did I miss something essential? The compiler I use is Borland Delphi 2006

Answer 1

WideCompareStr returns 0 if both strings are equal. So code:

WideCompareStr(FName,'')<>0

Returns false because both strings ARE equal which is what you are expecting (I guess!).

EDIT:

I am confused now. I just checked and in following code:

procedure TForm1.Button1Click(Sender: TObject);
var
  s1: WideString;
  r1, r2: Integer;
begin
  s1 := '';

  r1 := WideCompareStr (s1, '');
  MessageDlg (IntToStr (r1), mtWarning, [mbOK], 0);

  r2 := WideCompareStr (Trim (s1), '');
  MessageDlg (IntToStr (r2), mtWarning, [mbOK], 0);
end;

Both r1 and r2 are zero which is as expected. And your second line is actually a syntax error (Trim can receive only one parameter).