How can I initialize a record declared as a local variable?

Question

I'm using a record composed of strings, booleans, integers, currencies and arrays of other records inside a method of a class. I would like to recursively initialize all fields of a primitive type to empty/false/zero. Delphi doesn't appear to do this by default. Is there a straightforward way to accomplish this that doesn't involve accessing each field by name and setting it manually?

Note that Delphi initializes lifetime-managed types (strings, dynamic arrays, interfaces). — kludg, Aug 13 '10 at 14:41
In Delphi-2009 and later a record can be initialized by `Foo := Default(TFoo);`. See [David's answer](http://stackoverflow.com/a/11066205/576719) to the question [How to properly free records that contain various types in Delphi at once?](http://stackoverflow.com/q/11065821/576719). — LU RD, Jun 16 '12 at 20:24
also see: [Which variables are initialized when in Delphi?](http://stackoverflow.com/questions/861045/which-variables-are-initialized-when-in-delphi) — Gabriel, Jan 27 '17 at 10:46

score 13 · Accepted Answer · edited May 23 '17 at 12:17

13

You can use either one of following constructs (where Foo is a record).

FillChar(Foo, SizeOf(Foo), 0); 

ZeroMemory(@Foo, SizeOf(Foo));

From a post from Allen Bauer

While looking at the most common uses for FillChar in order to determine whether most folks use FillChar to actually fill memory with character data or just use it to initialize memory with some given byte value, we found that it was the latter case that dominated its use rather than the former. With that we decided to keep FillChar byte-centric.

edited May 23 '17 at 12:17

Community

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answered Aug 13 '10 at 14:30

Lieven Keersmaekers

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4

Or same code with (probably) better readability: ZeroMemory(@Foo, SizeOf(Foo)); – Im0rtality Aug 13 '10 at 14:34
@Im0rtality: I have updated the answer to include your ZeroMemory solution. – Lieven Keersmaekers Aug 13 '10 at 14:47
Note that ZeroMemory is a wrapper for FillChar in *some* versions of Delphi (d6 and 7 at least). – Gerry Coll Aug 14 '10 at 03:53
You should not use this, when the record contains managed types like strings or interfaces – R. Hoek Apr 26 '22 at 20:03

score 2 · Answer 2 · edited May 23 '17 at 12:02

2

Note, that you should use Finalize before FillChar or ZeroMemory in some cases.

edited May 23 '17 at 12:02

Community

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answered Aug 14 '10 at 08:54

Alex

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score 1 · Answer 3 · answered Apr 17 '20 at 23:17

well, you may apply a simple legal trick

unit unit1;

interface

type
  PMyRecord = ^TMyRecord;
  TMyRecord = record
    Value: Integer;
    function Self: PMyRecord;
  end;

implementation

function TMyRecord.Self: PMyRecord;
begin
  Result := @Self;
end;

procedure Test(AValue: Integer);
const MyRecord: TMyRecord = (Value: 0);
begin
  MyRecord.Self.Value := AValue;
end;

score 1 · Answer 4 · answered Apr 26 '22 at 10:57

1

Since Delphi 2007, you can use the Default() intrinsic function:

var
  LRecord: TMyRecord;
begin
  LRecord := Default(TMyRecord);
  ...

answered Apr 26 '22 at 10:57

Nat

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How can I initialize a record declared as a local variable?

4 Answers4