Can we implement ANSI C's `offsetof` in Delphi?

Question

For reference: The offsetof macro(!) takes a struct data type and a member of the specified struct as arguments and returns an integer offset of th

Answer 1

Without a pre-processor or a built-in function, there's no way to do it quite as cleanly as the offsetof macro. The way that offsetof is able to do it so cleanly is that the pre-processor does the work. In fact some compilers implement it as a built-in, but that's beside the point. Delphi has no pre-processor, and no built-in offsetof.

The cleanest solution I know is like this:

NativeUInt(@TMyRecord(nil^).MyField)

But that is nothing like as clean as

offsetof(struct MyStruct, MyField)

Answer 2

To expand on @DavidHeffernan's answer and @UliGerhardt's comment, here's what we now use, tested and in use:

procedure foo;
type
  TPerson = record
    DOB: TDate;
    FirstName: string;
    LastName: string;
  end;
const
  Offset_TPerson: ^TPerson = nil;
begin
  writeln('OffsetOf FirstName = '+IntToStr(NativeUInt(@Offset_TPerson.FirstName)));
end;