RE: nested unnamed structs/unions broken?

RE: nested unnamed structs/unions broken?

[Steve Watt]

Then that needs a doc fix, as it isn't mentioned anywhere.  The headers in question aren't from MS, they were developed in-house.  Guess we need to change them for 3.4.
 
Thanks for the info.

	-----Original Message----- 
	From: Jim Wilson [mailto:wilson@specifixinc.com] 
	Sent: Sun 10/26/2003 11:44 AM 
	To: Steve Watt 
	Cc: gcc-bugs@gcc.gnu.org 
	Subject: Re: nested unnamed structs/unions broken?
	
	

	Steve Watt wrote:
	> union optid {
	>     unsigned int opcode_tid;
	>     struct {
	>         unsigned int opcode:8;
	>         unsigned int tid:24;
	>     };
	> };
	
	You now need the -fms-extensions option in order for gcc to accept this.
	  This feature was originally added because it was used in MS Windows
	header files, and was thus needed by cygwin.  Some people objected to
	the feature when it accidentally turned up in other places, so now it
	only gets enabled if you explicitly ask for MSC compatibility.
	
	There is one case that gcc continues to accept by default, because it
	was agreed to be generally useful.  This is the case of a union inside a
	struct, where the union has no type name and no field name.  This is the
	case documented in the gcc manual in the Unnamed Fields node.
	http://gcc.gnu.org/onlinedocs/gcc-3.3.1/gcc/Unnamed-Fields.html#Unnamed%20Fields
	--
	Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com
	
	

RE: nested unnamed structs/unions broken?

[Jim Wilson]

On Sun, 2003-10-26 at 10:48, Steve Watt wrote:
> Then that needs a doc fix, as it isn't mentioned anywhere.

I agree.  Since your earlier bug report was already closed as invalid, I
took the liberty of creating another one.  This is now 12802 in
bugzilla.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com

Re: nested unnamed structs/unions broken?

[Jim Wilson]

Steve Watt wrote:
> union optid {
>     unsigned int opcode_tid;
>     struct {
>         unsigned int opcode:8;
>         unsigned int tid:24; 
>     };
> };

You now need the -fms-extensions option in order for gcc to accept this. 
  This feature was originally added because it was used in MS Windows 
header files, and was thus needed by cygwin.  Some people objected to 
the feature when it accidentally turned up in other places, so now it 
only gets enabled if you explicitly ask for MSC compatibility.

There is one case that gcc continues to accept by default, because it 
was agreed to be generally useful.  This is the case of a union inside a 
struct, where the union has no type name and no field name.  This is the 
case documented in the gcc manual in the Unnamed Fields node.
http://gcc.gnu.org/onlinedocs/gcc-3.3.1/gcc/Unnamed-Fields.html#Unnamed%20Fields
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com

nested unnamed structs/unions broken?

[Steve Watt]

The following code:

 - - - 8< - - -

#include <stdio.h>

union optid {
    unsigned int opcode_tid;
    struct {
        unsigned int opcode:8;
        unsigned int tid:24; 
    };
};

struct cpl_msg {
    union optid;
    int item1;
};

int main() {
    struct cpl_msg x;
    int opcode;
    int tid;

    x.opcode_tid = 0x000102da;

    printf("opcode %x tid %x\n", x.opcode, x.tid);

    exit(0);
}


 - - - >8 - - -

compiles and works with GCC 2.96 (ugh) and 3.2.2[FreeBSD] 20030205,
but with 3.4-20030819 (experimental), it fails during compilation:

     tpun.c:12: warning: declaration does not declare anything
     tpun.c: In function `main':

     tpun.c:21: error: structure has no member named `opcode_tid'
     tpun.c:23: error: structure has no member named `opcode'
     tpun.c:23: error: structure has no member named `tid'


I don't have a 3.3 handy to check against.  This feels like a bug
in 3.4, but I don't spot anything in the GCC Bugzilla that hints
towards it.

Thx,

-- 
Steve Watt       KD6GGD  PP-ASEL-IA       Email at  home: steve@watt.com
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