Value of string disappears

[Davidous]

Hello,

I'm new to Lazarus, I did a lot of programming in Delphi 7. Now I started to write my programs from Delphi to Lazarus, but I faced a very strange thing.

My program loads a text file to a stringlist. Then from this stringlist I need some lines as a string. I give these values to different strings. Then my program goes on and after a few more lines in the program when I check my string values I can see, that they are all ???... I suppose that means that they are empty. It is a really simple code, I don't know what could cause the problem. Please help me!

 oD:=TOpenDialog.Create(self);
 oD.InitialDir := GetCurrentDir;
 oD.Title:='Kérem válassza ki a mérési fájlt!';
 oD.Filter:='Txt fájlok|*.txt';
 oD.Execute;

 list:=TStringList.Create;
 list.LoadFromFile(oD.FileName);

 tr:=AnsiMidStr(list[0],22,length(list[0])-21);
 d:=AnsiMidStr(list[10],15,length(list[10])-14);
 fn:=ExtractFileName(oD.FileName);
 dl:=TStringList.Create;
 dl.Delimiter:='.';
 dl.DelimitedText:=d;

For w:=0 To 20 Do
Begin
If AnsiLeftStr(fn,4)='left' Then
Begin
If (AnsiMidStr(list[w],19,length(list[w])-18)='vorwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='steigend') Then
Begin
oldbj:='b';
Break;
end
Else If (AnsiMidStr(list[w],19,length(list[w])-18)='rückwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='fallend') Then
Begin
oldbj:='b';
Break;
end
Else If (AnsiMidStr(list[w],19,length(list[w])-18)='vorwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='fallend') Then
Begin
oldbj:='j';
Break;
end
Else If (AnsiMidStr(list[w],19,length(list[w])-18)='rückwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='steigend') Then
Begin
oldbj:='j';
Break;
end;
end
Else If AnsiLeftStr(fn,4)='righ' Then
Begin
If (AnsiMidStr(list[w],19,length(list[w])-18)='vorwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='steigend') Then
Begin
oldbj:='j';
Break;
end
Else If (AnsiMidStr(list[w],19,length(list[w])-18)='rückwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='fallend') Then
Begin
oldbj:='j';
Break;
end
Else If (AnsiMidStr(list[w],19,length(list[w])-18)='vorwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='fallend') Then
Begin
oldbj:='b';
Break;
end
Else If (AnsiMidStr(list[w],19,length(list[w])-18)='rückwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='steigend') Then
Begin
oldbj:='b';
Break;
end;
end;
end;

[Thaddy]

Well, compile in mode delphi. Your code works, but I had to do a lot to write a compilable version.

[Davidous]

I'm sorry, but I still can't get it to work. I set the compiler mode to delphi:

{$mode delphi}

but the result is the same. Strings are not stored for some reason.

[Blaazen]

What OS do you use and what is format of the text file (UTF8 or so)?
This may be related to different LineEnding in Windows and Linux.

[Davidous]

I use win10 but I also tested it on win7 with the same results.
The text file is UTF-8.

[HeavyUser]

two main problems
1)make sure that Ansileftstr,ansimidstr etc are returning the correct string.
2)change the comparison to use comparetext(string1,string2) = 0.

There are other points of failure as well, for example AnsiMidStr(list[w],19,length(list[w])-18), what happens if the string has an extra space or two at the end?

[Davidous]

Extra characters cannot be at the end, because the txt files I use are always generated by another program. This code worked without an error in delphi 7 but in Lazarus it doesn't. When I give the value to the string it stores it. I checked it during runtime, when I paused the proccess, but a few steps later all stored strings disappear.

[Davidous]

I attached some pictures. On the first one you can see, that everything seems to be all right, string value is what it is supposed to be. A few steps later I changes, you can see that on the second picture. (That try-except is only for stopping the program at the right moment, it is not part of the program.)

[Blaazen]

There are breakpoints for stopping program at the right moment.
The fact that hovering over identifier fn shows ??? in tooltip does not mean that content of string is lost. It rather means that code is out of scope.

[Bart]

Please attach a compilable sample program with the text-file it reads.
Also state what the expected output should be.

Bart

[Davidous]

Hello Bart!

I zipped my project, it is attached. I attached also one txt file it reads.
The output shold be a message with the text: 'A helyes oldal: b'.
Right now the message only shows 'A helyes oldal: '.

[balazsszekely]

@Davidous

The encoding of the txt file is wrong(attachment1), if I fix it(attachment2) you program displays the desired output. Download the modified txt and run a few tests yourself. By the way your code formatting is horrible(saláta). Please take it as a constructive criticism. It should look more like this:

Code: Pascal  [Select][+][-]

1.  For w:=0 To 20 Do
2.   Begin
3.     If AnsiLeftStr(fn,4)='left' Then
4.     Begin
5.       If (AnsiMidStr(list[w],19,length(list[w])-18)='vorwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='steigend') Then
6.       Begin
7.         oldbj:='b';
8.         Break;
9.       end
10.       Else If (AnsiMidStr(list[w],19,length(list[w])-18)='rückwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='fallend') Then
11.       Begin
12.         oldbj:='b';
13.         Break;
14.       end
15.       Else If (AnsiMidStr(list[w],19,length(list[w])-18)='vorwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='fallend') Then
16.       Begin
17.         oldbj:='j';
18.         Break;
19.       end
20.       Else If (AnsiMidStr(list[w],19,length(list[w])-18)='rückwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='steigend') Then
21.       Begin
22.         oldbj:='j';
23.         Break;
24.       end;
25.     end
26.     Else If AnsiLeftStr(fn,4)='righ' Then
27.     Begin
28.       If (AnsiMidStr(list[w],19,length(list[w])-18)='vorwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='steigend') Then
29.       Begin
30.         oldbj:='j';
31.         Break;
32.       end
33.       Else If (AnsiMidStr(list[w],19,length(list[w])-18)='rückwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='fallend') Then
34.       Begin
35.         oldbj:='j';
36.         Break;
37.       end
38.       Else If (AnsiMidStr(list[w],19,length(list[w])-18)='vorwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='fallend') Then
39.       Begin
40.         oldbj:='b';
41.         Break;
42.       end
43.       Else If (AnsiMidStr(list[w],19,length(list[w])-18)='rückwärts') And (AnsiMidStr(list[w+1],20,length(list[w+1])-19)='steigend') Then
44.       Begin
45.         oldbj:='b';
46.         Break;
47.     end;
48.   end;

[mangakissa]

Nice project. Especially for a school assignment.

[Davidous]

Thank you very much for your help!

[mangakissa]

I couldn't help it to make a class for (not all subjects are uses, but it gives an example how to work with).

Works in FPC end delphi. Using FPC remove the contnrs in uses

(rename the txt file to pas)