Record in record (Cannot initialize)

Question

I have 2 records like this:

TYPE
 TRecord2= packed record
  i2: Integer;
 end;

 TRecord1= packed record
  i1: Integer;
  R2: TRecord2;
 end;

.

I want to initialize the record fields to zero but I don't want to use FillMemory so I declared 2 constant records in which I initialize the fields.

CONST
  Record2c: TRecord2=
  (
   i2: 0;
  );

  Record1c: TRecord1=
  (
    i1: 0;
    R2: Record2c;      <------- error line
  );

However, I cannot assign a Record2c to R2 field. The compiler says: E2029 '(' expected but identifier 'Record2c' found.

But this works (if I comment the line where I have the error):

procedure test;
var Record1: TRecord1;
begin
 Record1:= Record1c;      // initialize variable by associating the constant to it
end

So, how do i initialize the R2 field?

Do you have a good reason to pack records? Memory can be slower that way. — , Jul 12 '11 at 16:13

score 5 · Answer 1 · answered Jul 12 '11 at 16:01

5

That's because Record2c is a typed constant which isn't a "real" constant. So you can't use it to initialize another constant. You have to declare Record1c like

  Record1c: TRecord1 =
    (
    i1: 0;
    R2: (i2: 0);
    );

answered Jul 12 '11 at 16:01

Uli Gerhardt

13,748
1
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score 5 · Accepted Answer · answered Jul 12 '11 at 16:03

5

You can only initialize consts with true constants. True constants do not have types — those are typed constants. See Declared Constants in the Delphi documentation. Record2c in your code is a typed constant, so it cannot be used in const expressions like the one required for initializing Record1c. You'll just have to in-line the definition of Record1c.R2:

const
  Record1c: TRecord1 = (
    i1: 0;
    R2: (i2: 0;);
  );

When you comment out the error line, you're leaving the R2 field default-initialized to zeros.

answered Jul 12 '11 at 16:03

Rob Kennedy

161,384
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Thanks. It is not exactly what I hoped for but it will do it. Accepted. – Gabriel Jul 12 '11 at 16:07
And another question: if the R2 filed will be declared like this "R2: array[1..1024] of Byte" how do I fill it with zeros? – Gabriel Jul 12 '11 at 16:35
That would have been better as a separate question: "How do I initialize an array field of a record constant?" Anyway, you initialize it with a list of values: `R2: (0, 0, 0, ...)`. Any items you don't specify will be set to zero. That only works with fixed-size arrays; the only constant expression allowed for dynamic arrays is `nil`. – Rob Kennedy Jul 12 '11 at 16:41
Added as new question: http://stackoverflow.com/questions/6667907/how-to-initialize-a-static-array – Gabriel Jul 12 '11 at 16:48

score 3 · Answer 3 · edited May 23 '17 at 12:08

3

In Delphi-2009 and later it is possible to zero a record by the Default call.

record1 := Default(TRecord1);  // This will zero record1 including R2

See David's answer to the question How to properly free records that contain various types in Delphi at once?.

edited May 23 '17 at 12:08

Community

1
1

answered Jun 16 '12 at 20:05

LU RD

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Record in record (Cannot initialize)

3 Answers3

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