In Delphi 4 I used dynamically sized arrays using setlength to resize them as needed.

I haven't been able to get it to work in FPC / Lazarus, and it looks like the setlength function isn't there. In fact, defining the array using:

var
	MyArray: array of TObject;

Doesn't work either...

This was a feature they added in Delphi 4. I've got over 60,000 lines of code that rely heavily on this that I was looking to migrate to Lazarus.

Have I just missed something, or must I write my own linked list manager or use a TCollection to get this to work?

Thanks,
Tony

the proper way would be to use a Property :

Type TMyObj = class(TObject)
Private
   FMyArray: ^TMyRecord
protected
  Function GetItem(Index : Integer) : TMyRecord;
public
   procedure Add(MyItem: TMyRecord);
   procedure Delete(MyIndex: Integer);
   function Count: Integer;
   property Items[Index: Integer] : TMyRecord read GetItem; Default;
end;

and you would put the actual routine in GetItem. The default allows you to read like myobj[0], aka you don't have to do a myobj.items[0]

Andrew

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Well this anoyed me to no end when I started working with FPC, but basically Dyn. Arrays don't exist in the FPC 1.0 branch, only in the unstable 1.1 branch. However, C dynamic arrays, aka Pointer arrays, do work. I am guessing you do not know how to do them, but it is really quite simple:

var
  myarray : ^TObject;
begin
  ...//do stuff
  reallocmem(myarray, 4*SizeOf(TObject));//allocmem to handle 4 objects
  myarray[2] := thisobject;//set the 3 entry
  ...//do stuff.
  reallocmem(myarray, 0);//free memory
end;

you simply use reallocmem in place of setlength, and multiply the length by the sizeof the type it contains.. at one point I actually created wrappers arround this to make more like Delphi dynamic arrays..but its been awhile so I do not know if I still have it. essentially though you should be able to port a lot of code with ease. by doing some sort of wrappers.. etc.

Andrew

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That's been working great! Thanks...

Next question: How can I return one from an object similar to TStrings? I checked the LCL sources and couldn't figure it out.

Here's what I want:

Type TMyObj = class(TObject)
Private
  FMyArray: ^TMyRecord
public
  procedure Add(MyItem: TMyRecord);
  procedure Delete(MyIndex: Integer);
  function Count: Integer;
  function Items{here's where I lose it - is it Items(Index: Integer)?}
end;
{Sample usage:}
MyObj := TMyObj.Create;
MyObj.Add(ThisItem); // adds an item to the array
MyItem := MyVar.Items[1]; // grabs the first item on array

Thanks!
Tony

Did someone try lazarus with 1.1 recently?

Yes, I do from time to time. The compilation issues changes over time. Currently it has problems with overriden methods of RTTI classes (TPersistent):

graphics.pp(189,15) Warning: An inherited method is hidden by "TFont.Assign(const tagLOGFONTA)"
graphics.pp(188,15) Error: There is no method in an ancestor class to be overridden: "TFont.Assign(TPersistent)"

Both errors make no sense to me.

Mattias

The 1.1 development compiler supports dynamic arrays.

Not exactly.. Basically you are dealing with a Pointer to a Pointer, if you were using ^Pointer or PPointer you would get the same results. I do not know why this make a difference, but it does. Basically this means you need to initialize the variable first with

new(MyPrints);

and finalize when done with

dispose(MyPrints);

Or use a pointer and type cast every time, which is clumsy, so I suggest you do it this way.

Andrew

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Andrew (and others):

I've successfully been using the above to manage arrays of records, but I finally tried to do objects this way and it won't work. Here's the code snippett:

procedure TFrmMain.PrintChecks;
var
   MyPrints: ^TChkTransaction; // array of transactions to print
begin
     writeln('Reallocating memory');
     reallocmem(MyPrints, 0);
     writeln('Zeroed.');
end;

Notice, I define a pointer and then attempt to make sure that the array is zero length to begin with (actually I added this just because I was testing why it crashed when I tried to set it the first time.)

It access violations before the writeln('Zeroed.') is executed.

At this point, I can't think of any reason it would cause a crash. All I have is a pointer and I attempt to reallocate the memory for it...

It crashes on reallocmem regardless of the size I specify: reallocmem(MyPrints, 0)
and
reallocmem(MyPrints,(2 * sizeof(TChkTransaction))) both result in a crash. Am I doing something wrong?

-Tony