Lazarus

Programming => General => Topic started by: nikel on December 09, 2022, 01:34:48 am

Title: [Solved] Throw error if string is empty
Post by: nikel on December 09, 2022, 01:34:48 am

Hello I know that 0 * 0 = Meaningless. But below code doesn't work:

Code: Pascal  [Select][+][-]

1. try
2.   Num:=Length(TempStrPtr^) * 0;
3. except
4.   on E: Exception do
5.   begin
6.     raise Exception.Create('KEY or TKEY tag not found. ' + #13#10 + E.Message);
7.     CreateIndexUnset;
8.     Halt(-1);
9.   end;
10. end;

How can I make it throw an error when string is null?

Title: Re: Throw error if string is empty
Post by: Thaddy on December 09, 2022, 01:59:21 am

Congratulations! Almost every line of code is dubious or an error.
The most important error being line 6, so line 7 and 8 are never executed.
But line 2 is also a point of concern, without proper context it may or may not "work", but it is horrible coding (and I do not mean the silly multiplication).

Title: Re: Throw error if string is empty
Post by: KodeZwerg on December 09, 2022, 03:20:17 am

Idk... idk...

Code: Pascal  [Select][+][-]

1. program project1;
2.  
3. {$IFDEF MSWINDOWS}{$APPTYPE CONSOLE}{$ENDIF}
4.  
5. uses
6.   SysUtils;
7.  
8. type
9.   TStringObject = class(TObject)
10.     strict private
11.       FAnsiString: AnsiString;
12.       FWideString: WideString;
13.     private
14.       procedure SetAnsiString(const AValue: AnsiString);
15.       procedure SetWideString(const AValue: WideString);
16.     public
17.       constructor Create;
18.     public
19.       property Ansi: AnsiString read FAnsiString write SetAnsiString;
20.       property Wide: WideString read FWideString write SetWideString;
21.   end;
22.  
23. constructor TStringObject.Create;
24. begin
25.   inherited Create;
26.   FAnsiString := '';
27.   FWideString := '';
28. end;
29.  
30. procedure TStringObject.SetAnsiString(const AValue: AnsiString);
31. begin
32.   if (AValue <> '') then
33.     FAnsiString := AValue
34.     else
35.     raise Exception.Create('Can not be Empty!');
36. end;
37.  
38. procedure TStringObject.SetWideString(const AValue: WideString);
39. begin
40.   if (AValue <> '') then
41.     FWideString := AValue
42.     else
43.     raise Exception.Create('Can not be Empty!');
44. end;
45.  
46. var
47.   so: TStringObject;
48. begin
49.   so := TStringObject.Create;
50.   try
51.     WriteLn('Try');
52.     try
53.       so.Ansi := 'Next raise an exception.';
54.       WriteLn(so.Ansi);
55.       so.Ansi := ''; // *boom*
56.       WriteLn(so.Ansi);
57.     except
58.       WriteLn('Exception');
59.     end;
60.   finally
61.     so.Free;
62.     WriteLn('Finally');
63.   end;
64.   WriteLn('Press Return');
65.   ReadLn;
66. end.

Title: Re: Throw error if string is empty
Post by: Bart on December 09, 2022, 03:38:45 pm

Why do you insist on using pointers to strings?

Bart

Title: Re: Throw error if string is empty
Post by: jamie on December 09, 2022, 03:46:30 pm

Quote from: Bart on December 09, 2022, 03:38:45 pm

Why do you insist on using pointers to strings?

Bart

He's probably an old cuke/fart like most of us here.

Title: Re: Throw error if string is empty
Post by: Thaddy on December 09, 2022, 06:23:32 pm

No he comes from null instead of nil. Read the original post. Anyway, good enough code for a T-shirt with a red cross allover it.  8-)

Title: Re: Throw error if string is empty
Post by: nikel on December 09, 2022, 09:06:03 pm

I tried it one more time and it worked:

Code: Pascal  [Select][+][-]

1. try
2.   WriteLn(Length(BpmPtr^) / Length(BpmPtr^));
3. except
4.   on E: Exception do
5.   begin
6.     raise Exception.Create('bpm tag not found. ' + #13#10 + E.Message);
7.     GetAllTagsByPathUnset;
8.     Halt(-1);
9.   end;
10. end;

Thanks for the replies.