(j3.2006) Union in Fortran

[Bader, Reinhold]

Hello Malcolm,

Von: j3-bounces at mailman.j3-fortran.org [mailto:j3-bounces at mailman.j3-fortran.org] Im Auftrag von Cohen Malcolm
Gesendet: Mittwoch, 14. September 2016 09:44
An: fortran standards email list for J3 <j3 at mailman.j3-fortran.org>
Betreff: Re: (j3.2006) Union in Fortran

No, this is not conforming.  The pointer assignment ?o => this? is not conforming when the dynamic type is not t.  Yes it is theoretically possible for compilers to detect this nonconformance (but none do at the moment as far as I know).

Thanks for pointing this out. I was relying on sequence association, and overlooked the additional rule.

In fact I don?t see the advantage in this design.  Just using extensible types instead of sequence types gives you the same facility but actually is standard-conforming and does not rely on the ?tag? being maintained by the user code.

Fully agree. The example was intended as a curiosity (and made up quite some time ago when the topic was raised).


I agree with Steve that using TRANSFER is the usual way of handling things like C unions if you want to be standard-conforming.
From: Bader, Reinhold
Sent: Wednesday, September 14, 2016 1:00 AM
To: fortran standards email list for J3
Subject: Re: (j3.2006) Union in Fortran

See attached code example. Quite clunky, but conforming, I believe.

I think you can do a similar example with BIND(C) types, using the TYPE(*) from TS29113.

Cheers
Reinhold

Von: j3-bounces at mailman.j3-fortran.org<mailto:j3-bounces at mailman.j3-fortran.org> [mailto:j3-bounces at mailman.j3-fortran.org] Im Auftrag von Daniel C Chen
Gesendet: Dienstag, 13. September 2016 17:52
An: j3 at mailman.j3-fortran.org<mailto:j3 at mailman.j3-fortran.org>
Betreff: (j3.2006) Union in Fortran


Hello,

Is there anyway in Fortran that I can do the equivalence of the following C code?

struct {
  int key;
  union {
    float t;
    int value;
  }
} s;


Thanks,

Daniel

XL Fortran Development - IBM Toronto Software Lab
Phone: 905-413-3056
Tie: 969-3056
Email: cdchen at ca.ibm.com<mailto:cdchen at ca.ibm.com>
http://www.ibm.com/software/awdtools/fortran/xlfortran

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........................Malcolm Cohen, Nihon NAG, Tokyo.
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