FileCreate and FileOpen return THandle with FPC but integer with Delphi2007. Delphi defines THandle as LongWord but for some reason Integer is used instead. With FPC on a 64-bit system THandle is 64- bit unsigned.

Question: what is the best way to maintain code that must compile with both FPC and Delphi2007?
The obvious solution is to use IFDEF and define a new type, say TMyHandle. FPC's libraries however take care of many platform differences. Is there any better way to solve this?

Regards,
Juha

Shortly said: No. The Delphi API is wrong; It should also return THandle (as that is what Windows CreateFile returns), but probably for historical reasons they still use Integer.
With the advent of 64-bit delphi, they could have cleaned up their API, but Alas...

Michael.

In our previous episode, Michael Van Canneyt said:

IMHO the universal handle (for e.g. IPC related handles and file handles) is not a portable concept to begin with.

Normally, I'd expect a TXYZHandle for each 'separate' type. With XYZ = File, Window, Lib, Module, Directory, Shmem, whatnot. This should cover most cases.

That these separate types are equal in the background is something the user need not know.

Michael.

I did try googling and it appears, that in 64 bit Delphi XE2 uses THandle as a result type. Anyway, in the case of error, it returns INVALID_HANDLE_VALUE, which is DWORD(-1).
So, under Windows it would be possible to use same code, if you compare result against INVALID_HANDLE_VALUE. And you should be able safely cast return value to THandle for that (and use variable of that type).
I really don't know, how it would work on linux, because sys_open seems to return int there.

Marco van de Voort wrote

IMHO the universal handle (for e.g. IPC related handles and file handles) is not a portable concept to begin with.

I think the concept of a handle as an opaque type is universal. What isn't safe is any assumption of consistent behaviour, e.g. that select() may be applied to any type of handle or that a program's stdin/stdout might in practice be implemented by a socket.

In our previous episode, Mark Morgan Lloyd said:

Before that, I don't even think sizeof(any handle)=constant for a given target is a valid assumption.

Thanks Virgo for this note. I was just thinking of how to check for errors. In many places our Delphi code has :

  if Handle-1 then begin
    ...
  end;

I will not define a new type after all, instead I will use THandle everywhere and then compare against INVALID_HANDLE_VALUE which is defined in Windows unit also for Delphi2007.
The only downside is that Delphi compiler will complain about incompatible types (signed / unsigned) when assigning FileCreate() etc. return values. I must use typecast then but it is OK.

Regards,
Juha