[Bug c/28368] New:

[Bug c/28368] New:

[gcc-bugzilla at gcc dot gnu dot org]

        -std=c89 doesn't warn about gcc's "?:" extension

Environment:
System: Linux rho 2.6.15-1-amd64-k8 #2 Tue Mar 7 06:53:26 UTC 2006 x86_64
GNU/Linux
Architecture: x86_64


host: x86_64-unknown-linux-gnu
build: x86_64-unknown-linux-gnu
target: x86_64-unknown-linux-gnu
configured with: /mirror/d/gcc/configure --disable-nls
--prefix=/p/p/gcc-2006-06-29.18h54 --disable-multilib --enable-languages=c

How-To-Repeat:

For example, I expected this to fail:

  echo 'int main() { return 3 ?: 1; }' > k.c
  gcc -W -Wall -std=c89 k.c

With --pedantic, I do get a warning:

  $ gcc --pedantic -std=c89 k.c
  k.c: In function 'main':
  k.c:1: warning: ISO C forbids omitting the middle term of a ?: expression

I suppose that using -std=c99 should evoke a warning, too.


-- 
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jim at meyering dot net
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[lloyd at randombit dot net]

------- Comment #1 from lloyd at randombit dot net  2007-03-07 14:47 -------
This is also true for C++ unless -pedantic is specified (which is confusing
since I thought -pedantic-errors was the default for C++, but apparently this
changed at some point). Using '-Wall -Wextra -ansi -std=c++98' gives no
warning.

I'm not sure if it's really a bug, since the GCC docs make it pretty clear that
-ansi et. al. are basically useless in terms of getting it to warn you about
using extensions, but it is certainly unexpected.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[manu at gcc dot gnu dot org]

------- Comment #2 from manu at gcc dot gnu dot org  2007-03-07 17:57 -------
The documentation says that you should use -pedantic to warn about GCC
extensions[*], so I am not sure whether this is valid. But honestly, from the
description of "-std=", I would understand that GNU extensions are disabled
when using -std=c89 or that pedantic does not warn for them when using
-std=gnu89, but neither of those are true.

[*] http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html#C-Extensions


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[joseph at codesourcery dot com]

------- Comment #3 from joseph at codesourcery dot com  2007-03-07 18:04 -------
Subject: Re:  -std=c89 doesn't warn about gcc's "?:" extension

On Wed, 7 Mar 2007, manu at gcc dot gnu dot org wrote:

> The documentation says that you should use -pedantic to warn about GCC
> extensions[*], so I am not sure whether this is valid. But honestly, from the
> description of "-std=", I would understand that GNU extensions are disabled
> when using -std=c89 or that pedantic does not warn for them when using
> -std=gnu89, but neither of those are true.

The key concept is that of base standard, as described in this passage 
from invoke.texi:

Where the standard specified with @option{-std} represents a GNU
extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
corresponding @dfn{base standard}, the version of ISO C on which the GNU
extended dialect is based.  Warnings from @option{-pedantic} are given
where they are required by the base standard.  (It would not make sense
for such warnings to be given only for features not in the specified GNU
C dialect, since by definition the GNU dialects of C include all
features the compiler supports with the given option, and there would be
nothing to warn about.)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[manu at gcc dot gnu dot org]

------- Comment #4 from manu at gcc dot gnu dot org  2007-03-07 18:11 -------
(In reply to comment #3)
> Subject: Re:  -std=c89 doesn't warn about gcc's "?:" extension
>
> Where the standard specified with @option{-std} represents a GNU
> extended dialect of C, such as @samp{gnu89} or @samp{gnu99}, there is a
> corresponding @dfn{base standard}, the version of ISO C on which the GNU
> extended dialect is based.  Warnings from @option{-pedantic} are given
> where they are required by the base standard.  (It would not make sense
> for such warnings to be given only for features not in the specified GNU
> C dialect, since by definition the GNU dialects of C include all
> features the compiler supports with the given option, and there would be
> nothing to warn about.)
> 

Sorry, I still don't understand what is the difference between -std=c89 and
-std=gnu89.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[joseph at codesourcery dot com]

------- Comment #5 from joseph at codesourcery dot com  2007-03-07 21:06 -------
Subject: Re:  -std=c89 doesn't warn about gcc's "?:" extension

On Wed, 7 Mar 2007, manu at gcc dot gnu dot org wrote:

> Sorry, I still don't understand what is the difference between -std=c89 and
> -std=gnu89.

-std=c89 accepts C89 programs that conflict with the GNU C89 language.  
For example, ones using "inline" or "asm" as an identifier, or using any 
non-reserved identifier predefined as a macro in GNU C (such as "linux" or 
"i386") or using trigraphs.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[manu at gcc dot gnu dot org]

------- Comment #6 from manu at gcc dot gnu dot org  2007-03-08 15:52 -------
(In reply to comment #5)
> Subject: Re:  -std=c89 doesn't warn about gcc's "?:" extension
> 
> On Wed, 7 Mar 2007, manu at gcc dot gnu dot org wrote:
> 
> > Sorry, I still don't understand what is the difference between -std=c89 and
> > -std=gnu89.
> 
> -std=c89 accepts C89 programs that conflict with the GNU C89 language.  
> For example, ones using "inline" or "asm" as an identifier, or using any 
> non-reserved identifier predefined as a macro in GNU C (such as "linux" or 
> "i386") or using trigraphs.
> 

That clarifies all perfectly. I think it is not as clear in the manual but
perhaps I am a bit slow. Maybe in -std= it should say:

gnu89
-              Default, ISO C90 plus GNU extensions (including some C99
fea‐
-              tures).
+              Default, subset of ISO C90 that doesn't conflict 
+              with GNU extensions (including some C99 features 
+              that conflict with C90)


In any case, this bug seems invalid to me.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[manu at gcc dot gnu dot org]

------- Comment #7 from manu at gcc dot gnu dot org  2008-01-18 12:09 -------
(In reply to comment #1)
> This is also true for C++ unless -pedantic is specified (which is confusing
> since I thought -pedantic-errors was the default for C++, but apparently this
> changed at some point). Using '-Wall -Wextra -ansi -std=c++98' gives no
> warning.
> 

Jack, why would you use "-ansi -std=c++98" in the same command-line? From
reading the current manual (for example,
http://gcc.gnu.org/onlinedocs/gcc-4.2.2/gcc/), what do you think that
combination achieves?

I am trying to improve this part of the manual. See my current patch at
http://gcc.gnu.org/ml/gcc-patches/2008-01/txt00033.txt


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[manu at gcc dot gnu dot org]

------- Comment #8 from manu at gcc dot gnu dot org  2008-02-16 16:29 -------
Subject: Bug 28368

Author: manu
Date: Sat Feb 16 16:29:12 2008
New Revision: 132367

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=132367
Log:
2008-02-16  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

        PR c/28368
        * doc/invoke.texi (-std): Clarify description of -std= and -ansi.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/doc/invoke.texi


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[manu at gcc dot gnu dot org]

------- Comment #9 from manu at gcc dot gnu dot org  2008-02-16 18:16 -------
Subject: Bug 28368

Author: manu
Date: Sat Feb 16 18:15:20 2008
New Revision: 132368

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=132368
Log:
2008-02-16  Manuel Lopez-Ibanez  <manu@gcc.gnu.org>

        PR c/28368
        * doc/invoke.texi (-std): Clarify description of -std= and -ansi.

Modified:
    branches/gcc-4_2-branch/gcc/ChangeLog
    branches/gcc-4_2-branch/gcc/doc/invoke.texi


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368

[Bug c/28368] -std=c89 doesn't warn about gcc's "?:" extension

[manu at gcc dot gnu dot org]

------- Comment #10 from manu at gcc dot gnu dot org  2008-02-16 18:20 -------
The new description in GCC 4.3 and GCC 4.2.4 should clarify this from now on.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.2.4


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28368