Array within an array??

[Ian Branch 128]

Hi Team,

Need some help/guidance.

I have an array of labels 12 x 7.  These I can address by something like 'Matrix[0,1] to Matrix[12,7]'.

Each label will have an integer value, and colour integer associated with it.  e.g.  [124, 255] the 124 in this case to be converted to string for the label's caption.

How do I define an array, possible an array within a matrix, to accommodate this?

Having defined the array how do I address an individual item in one of the label's array?

 

Regards & TIA,

Ian

[David Heffernan 2354]

It's just a multidimensional array of record. 

 

You will need to decide whether it is zero based or one based, but your example above shows a range of at least 13 in the major axis. 

[Ian Branch 128]

Hi David,

I figured it was going to be a multidimensional array of record.

So I tried the following..

type
  TForm26 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
    type
    TLabelRecord = record
      iValue: Integer;
      iColor: Integer;
    end;
    LabelMatrix = array of array of TLabelRecord;

  public
    { Public declarations }
  end;

var
  Form26: TForm26;

implementation

{$R *.dfm}

procedure TForm26.Button1Click(Sender: TObject);
begin
SetLength(LabelMatrix, 11, 6);


end;

Delphi tells me the SetLength code in the Button Click is wrong, object (LabelMatrix) cannot be passed as a parameter, but I don't know why.  😞

I don't care if it starts at 0 or 1, whatever the default is.

I don't know what to do from here.. 😞

[David Heffernan 2354]

LabelMatrix is a type. You need to declare a variable of that type. Why would you have a dynamic array if the dimensions are known. Also, why 11, 6 if it is 12x7.  If it is a fixed size, declare it so.

 

Structured Types (Delphi) - RAD Studio (embarcadero.com)

[Ian Branch 128]

Hi David,

OK.  I think I understand.  So now I have..

type
  TForm26 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
    type
      TLabelRecord = record
        iValue: Integer;
        iColor: Integer;
      end;

    type
      TLabelMatrix = array[1..12, 1..7] of TLabelRecord;

  public
    { Public declarations }
  end;

var
  Form26: TForm26;

implementation

{$R *.dfm}

procedure TForm26.Button1Click(Sender: TObject);
var
  rRec: TLabelRecord;
  mLabelMatrix: TLabelMatrix;
begin



end;

But how do I address one element of rRec within one element of mLabelMatrix?

[Fr0sT.Brutal 900]

Why don't you just read language ref, all this is basic language elements.

[Ian Branch 128]

I surrender.

I have gone to two arrays..

    LabelValue: array of array of Integer;
    LabelColor: array of array of Integer;

Thank you for your suggestions/advice.

 

Ian

[David Heffernan 2354]

15 minutes ago, Ian Branch said:

I surrender.

I have gone to two arrays..

    LabelValue: array of array of Integer;
    LabelColor: array of array of Integer;

Thank you for your suggestions/advice.

 

Ian

That's odd because you already solved the problem properly. Why do you just give up?

[David Heffernan 2354]

55 minutes ago, Ian Branch said:

But how do I address one element of rRec within one element of mLabelMatrix?

mLabelMatrix[i, j]

or if you prefer

mLabelMatrix[i][j]

as documented in the link I gave you

Edited June 6, 2022 by David Heffernan

[Ian Branch 128]

Because I wasn't seeing it and getting more and more confused so I decided to take the easy way out.

I put it down, had a coffee, and came back to it.

I now have it..

type
  TForm26 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
    type
      TLabelRecord = record
        iValue: Integer;
        iColor: Integer;
      end;

    type
      TLabelMatrix = array[1..12, 1..7] of TLabelRecord;

  public
    { Public declarations }
  end;

var
  Form26: TForm26;

implementation

{$R *.dfm}

procedure TForm26.Button1Click(Sender: TObject);
var
  LabelRecord1, LabelRecord2: TLabelRecord;
  LabelMatrix: TLabelMatrix;
begin
  LabelRecord1.iValue:= 123;
  LabelRecord1.iColor := 234;
  LabelMatrix[1,1] := LabelRecord1;
  //
  LabelRecord2 := LabelMatrix[1,1];
  ShowMessage('Value = '+LabelRecord2.iValue.ToString);
  ShowMessage('Color = '+LabelRecord2.iColor.ToString);
  //
end;

Thank you for your patience & guidance.

 

Ian

[Darian Miller 366]

4 hours ago, Ian Branch said:

I put it down, had a coffee, and came back to it.

 

 

Sometimes all it takes is to walk away from the problem for a short while.

[Lars Fosdal 1793]

A warning: Using records instead of objects in containers carries the penalty of duplication.

  LabelRecord1.iValue:= 123;
  LabelRecord1.iColor := 234;
  LabelMatrix[1,1] := LabelRecord1;
  LabelRecord1.iColor := 567;

At this point, LabekMatrix{1,1].iColor will still be 234.
It is the same the other way around.  Modify the array value, and the variable stays unchanged.

A workaround would be to use pointers.
type PLabelRecord = ^TLabelRecord;
and use variables and arrays of that type.
You would need to New/Dispose each reference, but at least there is no duplication as you pass around the pointer reference to the original allocation instead of copying the record like in the original example.  

[David Heffernan 2354]

1 hour ago, Lars Fosdal said:

A workaround would be to use pointers.
type PLabelRecord = ^TLabelRecord;
and use variables and arrays of that type.

Pretty bad idea this. It's also attempting to solve a problem that doesn't exist. 

 

Like if I do this:

 

i := 12;
j := i;
i := 14;

 

I don't expect j to become 14. It's just value type semantics.

[Lars Fosdal 1793]

True, it is only a problem if you pass the values around to be modified.

[David Heffernan 2354]

10 minutes ago, Lars Fosdal said:

True, it is only a problem if you pass the values around to be modified.

Same for integers, right? We don't feel compelled to store pointers to integers in arrays very commonly, do we.