[Bug c/12877] New: conditional as lvalue gives wrong warning

[Bug c/12877] New: conditional as lvalue gives wrong warning

[falk at debian dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12877

           Summary: conditional as lvalue gives wrong warning
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: falk at debian dot org
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: alphaev68-unknown-linux-gnu
  GCC host triplet: alphaev68-unknown-linux-gnu
GCC target triplet: alphaev68-unknown-linux-gnu

falk@juist:~% cat bug1.c       
void f (void) {
    char c, d;
    (1 ? c : d) = 0;
}

falk@juist:~% gcc -c bug1.c 
bug1.c: In function `f':

bug1.c:3: warning: use of cast expressions as lvalues is deprecated

But it's a conditional, not a cast, and I think this extension isn't
deprecated.

[Bug c/12877] conditional as lvalue gives wrong warning

[jsm at polyomino dot org dot uk]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12877



------- Additional Comments From jsm at polyomino dot org dot uk  2003-11-02 21:10 -------
Subject: Re:  New: conditional as lvalue gives wrong warning

On Sun, 2 Nov 2003, falk at debian dot org wrote:

> But it's a conditional, not a cast, and I think this extension isn't
> deprecated.

The cast is implicit; the semantics of conditional expressions mean that
the chars are converted to a common type of int before the conditional
expression is applied to them.  Essentially, the extension in question
wasn't properly thought out for anything other than the case of a common
type that is unaffected by the integer promotions.  The problem is
arguably that we don't get a hard error here.  A similar case where
instead of a straight assignment the conditional expression was being used
as an output for an asm was rejected (PR 11564); the types there were
different but the problem applies just as much where they are the same but
get promoted.

This extension only isn't deprecated *yet* so that the deprecations (and
any associated problems) could be dealt with one at a time.  PR 11427 has
a specific suggestion that it be deprecated and no objections thereto.  
I'm inclined on that basis to go ahead with deprecating conditional
expressions as lvalues in C for 3.4, and then follow with compound
expressions, also for 3.4.

[Bug c/12877] conditional as lvalue gives wrong warning

[falk dot hueffner at student dot uni-tuebingen dot de]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12877



------- Additional Comments From falk dot hueffner at student dot uni-tuebingen dot de  2003-11-02 21:36 -------
Subject: Re:  conditional as lvalue gives wrong warning

"jsm at polyomino dot org dot uk" <gcc-bugzilla@gcc.gnu.org> writes:

> > But it's a conditional, not a cast, and I think this extension isn't
> > deprecated.
> 
> The cast is implicit; the semantics of conditional expressions mean that
> the chars are converted to a common type of int before the conditional
> expression is applied to them.

Well, as a technical term, casts are always explicit; what happens is
a conversion. So IMHO the message is still wrong.

> Essentially, the extension in question wasn't properly thought out
> for anything other than the case of a common type that is unaffected
> by the integer promotions.  The problem is arguably that we don't
> get a hard error here.

C++ has deal with it, so if we really wanted to, it should be possible
to come up with sensible semantics.

> This extension only isn't deprecated *yet* so that the deprecations
> (and any associated problems) could be dealt with one at a time.  PR
> 11427 has a specific suggestion that it be deprecated and no
> objections thereto.  I'm inclined on that basis to go ahead with
> deprecating conditional expressions as lvalues in C for 3.4, and
> then follow with compound expressions, also for 3.4.

I agree.

[Bug c/12877] conditional as lvalue gives wrong warning

[pinskia at gcc dot gnu dot org]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12877


pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |patch
   Last reconfirmed|0000-00-00 00:00:00         |2003-11-05 04:25:22
               date|                            |
   Target Milestone|---                         |3.4


------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-05 04:25 -------
Patch to Deprecate this extension: <http://gcc.gnu.org/ml/gcc-patches/2003-11/
msg00262.html> and fixes the error.

[Bug c/12877] conditional as lvalue gives wrong warning

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-11-09 02:06 -------
The warning is correct but the warning abour conditional lvalue is not there. :(

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|patch                       |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12877

[Bug c/12877] conditional as lvalue gives wrong warning

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2003-12-21 23:40 -------
Not a regression but will be removed for 3.5 anyway so moving it to that.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2003-11-05 04:25:22         |2003-12-21 23:40:14
               date|                            |
   Target Milestone|3.4.0                       |3.5.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12877

[Bug c/12877] conditional as lvalue gives wrong warning

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-01-23 03:46 -------
Closing as will not fix as the error says invalid lvalue in assignment now.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12877