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A question about arrays in classes...

My question/problem is this:

Interface

TSomething = Class
Private
Max : integer;
A : Array[1..max] of Tobject;
Public
constructor Create(M:integer);
end;

Implementation

Constructor TSomething.Create(max:integer);
Begin
Max := M;
end;

The above gives an error since the compiler does not know the 'max'-variable when it tries to make the array.

This can of course be solved by making 'max' a constant outside the class-definition. But is there not another way to do it, so that the create decides the size of the array???

Retep

ASKER CERTIFIED SOLUTION

edey

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rwilson032697

You can do it using a dynamic array like this:

Interface

TSomething = Class
Private
Max : integer;
A : Array of Tobject;
Public
constructor Create(M:integer);
end;

Implementation

Constructor TSomething.Create(M:integer);
Begin
Max := M;
SetLength(A, M); // Note this is a zero based index so indices are 0..M-1
end;

Cheers,

Raymond.

edey

should note that, while both of our solutions use 'dynamic' arrays, rwilson's requires d4+.

GL
Mike

retep

ASKER

good ideas... As far as I can see, both solutions require Delphi4, since dynamic arrays came with Delphi4. Not a problem because I use Delphi4.

When I use your solutions with dynamic arrays, will the array then be fixed length, or will it still 'grow' dynamically?

Is there not a way to do it with a traditionally fixed-size-array?

Thanks
Retep

rwilson032697

The array will not grow dynamically by itself. If you want this to happen you should use a TList or TObjectList.

However, you can resize a dynamic array (ie: one declared like Fred: Array of Tx) any time you like, like this:

Procedure TSomeThing.AddItem(Item : TObject; Index : Integer);
begin
if Index >= Max then
begin
Max := Index + 1);
SetLength(A, Max);
end;

A[Index] := Item;
end;

You can't do it with a trditional fixed length array because, well, they are fixed length. :-)

Cheers,

Raymond.

lordcrc

From what you tell, it clearly seems like TList would be the thing to use here. TObjectList is created for this purpose, but i fail to remeber when the delphi version it entered the world (at least its in d5)

The TList would just as easy to use, just to a typecast.

The code would read something like:

type
TSomething = Class
private
FList: TList; // or TObjectList
public
constructor Create(Max: cardinal);
destructor Destroy; override;
end;

constructor TSomething.Create(Max: cardinal);
begin
FList:= TList.Create;
FList.Capacity:= Max;
end;

destructor TSomething.Destroy;
begin
FList.Free; // of cource free the objects that are in the list first
end;

Now.. to add an object do
FList.Add(MyObject)

to remove you use
Flist.Remove(MyObject)

and to access the objects
MyObject:= TObject(FList.Items[15]);

If you use TObjectList, you dont have to worry about the typecast when fetching objects

- Asbjørn

rwilson032697

As per my suggestion :-)

retep

ASKER

Thank you all for your comments. It's impossible for me to say which comment is the best since all of them have been very usefull... Therefore I have choosen to accept the first comment added.

Regards
Retep

edey

thank you :)
hope we have been helpfull, dynamic rasource management is an important topic, one def. worth exploring more :)

GL
Mike