Delphi -> Array of Byte to LongInt

Question

I want to take 4 Bytes from

Source : Array[0..500] of Byte;

where

c : integer; // Start Point

to

v : LongInt;

but

Move(Source[c], v, 4);

gives me only 1 Byte back. Where is my fault?

Thanks again.

There's nothing wrong with that code. BTW, I think Rudy's way is simpler: PLongint(@Source[c])^ — Sertac Akyuz
– Sertac Akyuz, Commented Nov 30, 2012 at 0:34
Works fine for me exactly as you have shown it. Make sure your c value is correct. — Remy Lebeau
– Remy Lebeau, Commented Nov 30, 2012 at 0:38
Move works as so many have said. In case you didn't understand my answer to your other question, use Move to copy then entire array. You don't need to do it element by element. — David Heffernan
– David Heffernan, Commented Nov 30, 2012 at 7:35
And yes, if you really just want a single integer, then use a pointer cast. — David Heffernan
– David Heffernan, Commented Nov 30, 2012 at 7:52

GolezTrol · Accepted Answer · 2012-11-30 00:37:15Z

5

This source works perfectly fine. It may however look like it returns only a byte if only the first byte (the one at index c) contains a value other than 0.

This alternative, already suggested by Sertac Akyuz, works fine as well:

v := PLongInt(@Source[c])^;

answered Nov 30, 2012 at 0:37

GolezTrol

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2 Comments

jachguate Over a year ago

@Michael only god knows? it's a simple pointer dereference over a cast over a pointer obtained via @ (at) operator!

jachguate Over a year ago

And the other way works either, as I demonstrate in my answer

jachguate · Accepted Answer · 2012-11-30 00:39:04Z

2

I doubt move is failing:

Try this code:

procedure TForm1.Button1Click(Sender: TObject);
var
  source: array[0..500] of Byte;
  C: Integer;
  V: LongInt;
begin
  source[0] := $55;
  source[1] := $55;
  source[2] := $55;
  source[3] := $55;
  C := 0;
  Move(Source[C], V, SizeOf(V));
  ShowMessage(IntToStr(V));
end;

You will see the number 1431655765 ($55555555) in the message.

answered Nov 30, 2012 at 0:39

jachguate

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