Why is PDWord not ^DWORD?

Question

This program

{$APPTYPE CONSOLE}
{$TYPEDADDRESS ON}

uses
  Winapi.Windows;

procedure Foo(P: PDWORD);
begin
end;

procedure Bar;
var
  dw: DWORD;
begin
  Foo(@dw);
end;

begin
end.

compiles in XE3, but does not in XE4, XE5, XE6 and XE7. The error is at

Foo(@dw);

[dcc32 Error] E2010 Incompatible types: 'PDWORD' and 'Pointer'

This feels odd. So, after a bit of digging it seems that the issue is down to the definition of PDWORD. One might naturally think that it would be:

PDWORD = ^DWORD;

and indeed that is the case in XE3. In later versions we find this:

// Note: Not ^DWORD yet
PDWORD = ^CppULongInt;

Odd. So, what is CppULongInt?

CppULongInt = type LongWord; 
{$EXTERNALSYM CppULongInt 'unsigned long'} 
{$OBJTYPENAME CppULongInt 'Bul' 'Gm'}

Then looking at the declaration for DWORD we find:

//NOTE: DWORD should really be CppULongInt
DWORD = LongWord;

So, CppULongInt and DWORD are different types. Hence the compilation error.

What's going on here? What is the purpose of CppULongInt? Why do the RTL designers appear to want to alias DWORD to CppULongInt. Is this change related to the x64 Windows C++ compiler based on LLVM? Am I the only person in the world that uses {$TYPEDADDRESS ON}?

Note, that last question is rhetorical.

Answer 1

(Refering to Why PDWORD is not a pointer to DWORD.) It looks someone at Embarcadero didn't read the relevant Windows documentation:

• DWORD is explicitly defined as a 32 bit unsigned integer, thereby in Delphi it should be an UInt32.
• PDWORD is defined as a pointer to a DWORD, thereby in Delphi it should be PDWORD = ^DWORD.
• It's DWORD_PTR (which is not a PDWORD!) that is defined as an ULONG_PTR, and the latter changes in size depending on the platform (32 or 64 bit), not the compiler definition of an unsigned long.

One reason may be they are attempting to use DWORD and other Windows datatypes on non Windows platforms, and are trying to keep them compatible. If so, in this case they failed and introduced a bug, because the definitions used won't work properly in Windows.