[Answered] Explanation of an odd type-construct?!?!?

[cdbc]

Hi everybody.

I'm wondering a little about the following type-construct:

Code: [Select]

type
  ppsqlite3 = ^psqlite3;
  psqlite3 = ^_sqlite3;
  _sqlite3 = record end; {code lifted from SQLite3 interface }

Is this "a pointer to a pointer to a structure containing no data-members" ????????????
or "a pointer to a unspecified pointer to an 4/8 byte memory block" ???????
or something completely different....

Please could someone explain this to me in details, as i'm puzzled????

TIA
Regards - Benny

[Vincent Snijders]

It is an opaque pointer. You are not allowed to / you should not care about the internals and just pass the pointer to it around.

[cdbc]

Thank you Vincent.

Regards Benny

[circular]

It's a pointer to a pointer to a structure containing members that cannot be accessed like usual structures. It can mean that you should not change it by yourself or that the members have variable width.

Anyway, it's a strange way to define it, because they could have simply define "psqlite3 = pointer".

[Vincent Snijders]

If you use psqlite3 = pointer, then it is assignment compatible with other pointers. Now the following won't compile in certain modes.

Code: [Select]

type
 psqlite3 = ^_sqlite3;
  _sqlite3 = record end;
 potherthings= ^_otherthings;
  _otherthings = record end;

var
  a : psqlite3;
  b: potherthings;
begin
  SomeSqliteProcedure(a); // works
  SomeSqliteProcedure(b); // error: wrong type passed
end;


[circular]

What about "psqlite3 = type pointer" ?

[Vincent Snijders]

Try for yourself :-)