[Solved] Dynarray of class cannot SetLength or Length
lazarus / 62-General

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NaolShow · 2021-11-10 09:36

Hi everyone, it's me again, I need some help with the dynarrays.
I already used them with simple data like Integers, but now I am
trying to make an Array of a class called BaseItem.

The problem is that it works perfectly when telling directly the size
of the array:
type ItemsArray = array[0..100] of BaseItem;
then:
Items : ItemsArray;
The Length(Items) works

But it does not work when I use a dynarray:
type ItemsArray = array of BaseItem;
then:
Items : ItemsArray;

If I try to call the Length(Items) it gives me the error:
External: SIGSEGV
at the line...
writeln(Length(Items))

And if I try with the SetLength(Items, 5):
External: SIGSEGV
at the address: 100008042

Is there any solution to this ? Or do I need to use a list ?
Thanks!

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NaolShow · 2021-11-10 09:48

I've tried in another project, and with juste the BaseI]"]>Blockednit
and a dynarray type in the main class it works perfectly..
So the problem is not from the array.

So here's my full code of the container unit:
Is it because the array is defined in a class ? (That's the only
difference with the test project)

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
ContainerUnit; {$mode objfpc}{$m+}{$R+} interface uses Classes,
SysUtils, BaseI]"]>Blockednit; type ItemsArray = array[0..5] of
BaseItem; type Container = class    public       Items : ItemsArray;  
    constructor Create();       function Add(item : BaseItem) :
Integer; end; implementation constructor Container.Create();begin 
//Items[0] := BaseItem.Create('tt');end; function Container.Add(item :
BaseItem) : Integer;begin   // It throws the errors when calling these
methods  writeln(Length(Items));  //SetLength(Items, 5); end; end.

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bytebites · 2021-11-10 11:12

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type
ItemsArray = array[0..5] of BaseItem;
This array has fixed length, you can't change it with setlength-
function.

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howardpc · 2021-11-10 11:25

Or to use a dynamic array, something like this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
project1; {$mode objfpc}{$H+}{$ModeSwitch advancedrecords} type  
TBaseItem = record    name: String;    value: Integer;    procedure
Init(const aName: String; aValue: Integer);  end;   TBaseItemArray =
array of TBaseItem;   TContainer = class(TObject)  private    function
GetCount: Integer;  public    Items: TBaseItemArray;    constructor
Create;    function Add(aItem: TBaseItem): Integer;    property Count:
Integer read GetCount;  end; { TBaseItem } procedure
TBaseItem.Init(const aName: String; aValue: Integer);begin  name :=
aName;  value := aValue;end; constructor TContainer.Create;begin 
Items := Nil;end; function TContainer.Add(aItem: TBaseItem):
Integer;begin  SetLength(Items, Length(Items)+1);  Result :=
High(Items);  Items[Result] := aItem;end; function
TContainer.GetCount: Integer;begin  Result := Length(Items);end; var 
cont: TContainer;  bi: TBaseItem; begin  cont := TContainer.Create;  
bi.Init('one', 1);  cont.Add(bi);  bi.Init('two', 2);  cont.Add(bi); 
WriteLn('cont has ',cont.Count,' items');   cont.Free;end.

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Zvoni · 2021-11-10 11:38

You should read this: https://www.freepascal.org/docs-
html/ref/refsu35.html

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PascalDragon · 2021-11-10 12:22

Quote from: NaolShow on November 10, 2021, 10:48:58 amSo here's my
full code of the container unit:
Is it because the array is defined in a class ? (That's the only
difference with the test project)
Did you do essentially the following in your main program?

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var  c:
Container;  bi: TBaseItem;begin  c := Container.Create;  bi :=
BaseItem.Create;  c.Add(bi);  // ...end.

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NaolShow · 2021-11-10 15:24

Hi everyone thanks for your reply.

I am so sorry for annoying you with that.
I am just incredibly STUPID. It was early and I was tired.
I didn't see that I did not INITIALIZE the Container variable.

This is because I am using a lot of units, and I have a Container
variable into but did not initialize it
in the initialize method...

Thanks again and sorry!

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PascalDragon · 2021-11-11 08:20

Quote from: NaolShow on November 10, 2021, 04:24:23 pmI didn't see
that I did not INITIALIZE the Container variable.

This is because I am using a lot of units, and I have a Container
variable into but did not initialize it
in the initialize method...

That's what I thought and that's why I asked.