[Bug c++/27235] New: goto crossing P.O.D. initialization

[Bug c++/27235] New: goto crossing P.O.D. initialization

[acahalan at gmail dot com]

I presume that the C++ standard requires this to be an error:

int foo(int arg){
  goto Hell;
  int i = arg;
Hell:
  return arg;  // or using i here
}

Especially in the case of plain old data (no constructor, etc.)
this behavior is needlessly incompatible with C.

Please require -pedantic -std=c++98 for such unfriendly behavior.


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           Summary: goto crossing P.O.D. initialization
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: acahalan at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-04-21 16:04 -------
First what version of GCC you are using?

Is it before 4.0.3?
If so this is a dup of bug 20721.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2006-04-21 16:18 -------
Please read http://gcc.gnu.org/bugs.html

and provide all the information there which in case means the version of gcc.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[acahalan at gmail dot com]

------- Comment #3 from acahalan at gmail dot com  2006-04-22 01:03 -------
I saw it on Fedora Core 5, which I believe is gcc 4.1, and I saw it on a gcc
which describes itself as:

gcc version 4.0.3 (Debian 4.0.3-1)

So that is two rather different gcc versions. One is x86-64, the other is
32-bit PowerPC. Am I wrong to assume that the latest gcc behaves this way?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2006-04-22 01:12 -------
What exactly do you want, no error unless you supply -std=c++98 -pedantic.

that is not going to change sorry.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[acahalan at gmail dot com]

------- Comment #5 from acahalan at gmail dot com  2006-04-22 07:12 -------
No legal C++ code would break if g++ were less incompatible with C. Why be
incompatible?

There are cases where gcc takes far greater liberties with the standards,
breaking fully legal code. (trigraphs for example) The proposed change would
allow for easier reuse of C code, which is certainly a benefit.

If the new rule is to follow standards to the letter by default, then trigraphs
are an urgent need. Otherwise, the goto behavior should change. I don't see how
it is justified to break valid code, yet refuse a change that would allow
greater compatibility with C.


-- 

acahalan at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2006-04-22 15:34 -------
GCC is not going to implement by default a non standard version of C++ (well
some extensions are on by default but those are usually more defined than
this).


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[falk at debian dot org]

------- Comment #7 from falk at debian dot org  2006-04-23 19:05 -------
I think this is a valid request. While random language extensions aren't
useful,
compatibility with C99 is. Maybe somebody else can comment on this...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[pinskia at gcc dot gnu dot org]

------- Comment #8 from pinskia at gcc dot gnu dot org  2006-04-23 20:21 -------
(In reply to comment #7)
> I think this is a valid request. While random language extensions aren't
> useful,
> compatibility with C99 is. Maybe somebody else can comment on this...

There are a lot of differences between C and C++, this is just one of the
differences.  Another would be where the variable is done inside a for/if
expression in that:
int g(void);
int f(void)
{
  if (int t = g())
  {
     int t = g()+1;
  }
}

is valid C but invalid C++ (though GCC gets it wrong for C++ but that is an
already filed bug report).
PR 27252 (aka PR 9278) is another example where C and C++ diff and in fact was
just fixed for 4.2.0 for a bug report.  These are just some examples of where C
and C++ differ.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[acahalan at gmail dot com]

------- Comment #9 from acahalan at gmail dot com  2006-04-23 20:39 -------
Regarding Comment #8:

Of course I do not want g++ to be a perfect superset of gcc. That is
unreasonable, because it would break legitimate standards-conforming C++ code.

I only ask that C compatibility be provided for code that would otherwise fail
to compile as C++. This makes code reuse much easier.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[pinskia at gcc dot gnu dot org]

------- Comment #10 from pinskia at gcc dot gnu dot org  2006-04-23 20:53 -------
(In reply to comment #9)
> I only ask that C compatibility be provided for code that would otherwise fail
> to compile as C++. This makes code reuse much easier.

I showed two other examples which are (were) reproted saying GCC accepted
invalid C++ (and the code was valid C and people actually used the second case
already in patricte which is why I pointed it out).

So if you want to modify the C++ front-end and to make an option, that is fine
but GCC should (and does have) a pratice of not accepting new extensions.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[acahalan at gmail dot com]

------- Comment #11 from acahalan at gmail dot com  2006-04-24 04:10 -------
When did gcc suddenly stop accepting new extensions?

For years gcc has been more of a practical real-world compiler than a pedantic
standards-only compiler. Many extensions have been added, both useful and
useless. Just look at the list of them.

Much of gcc's popularity has historically had to do with making things easy for
programmers. Don't let us down now that the alternatives have gone extinct.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[gdr at integrable-solutions dot net]

------- Comment #12 from gdr at integrable-solutions dot net  2006-05-01 20:45 -------
Subject: Re:  goto crossing P.O.D. initialization

"falk at debian dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| I think this is a valid request. While random language extensions aren't
| useful,
| compatibility with C99 is. Maybe somebody else can comment on this...

You have to be more precise about what you mean by C99 compatibility.

My take on this goto stuff, if it is not valid C++, it is valid C++.  Period.

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[gdr at integrable-solutions dot net]

------- Comment #13 from gdr at integrable-solutions dot net  2006-05-01 20:47 -------
Subject: Re:  goto crossing P.O.D. initialization

"pinskia at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| PR 27252 (aka PR 9278) is another example where C and C++ diff and in fact
was
| just fixed for 4.2.0 for a bug report.  These are just some examples of where
C
| and C++ differ.

I fully agree.
People have to be extra careful when they talk about compatibility
with C99 where the C committee has carefully chosen to depart from C++.

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[gdr at integrable-solutions dot net]

------- Comment #14 from gdr at integrable-solutions dot net  2006-05-01 20:48 -------
Subject: Re:  goto crossing P.O.D. initialization

"acahalan at gmail dot com" <gcc-bugzilla@gcc.gnu.org> writes:

| I only ask that C compatibility be provided for code that would otherwise
fail
| to compile as C++. This makes code reuse much easier.

Given prior existence in C++, I think logic would require that you ask
gcc to be compatibile with g++.

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[falk at debian dot org]

------- Comment #15 from falk at debian dot org  2006-05-01 20:55 -------
(In reply to comment #12)
> Subject: Re:  goto crossing P.O.D. initialization
> 
> "falk at debian dot org" <gcc-bugzilla@gcc.gnu.org> writes:
> 
> | I think this is a valid request. While random language extensions aren't
> | useful,
> | compatibility with C99 is. Maybe somebody else can comment on this...
> 
> You have to be more precise about what you mean by C99 compatibility.

I have trouble seeing what might be unclear about this term. I mean that code
that is valid C99 is accepted in C++ unless there is a good reason not to.
just like most of C89 is accepted in C++ unless there is a good reason not to.

> My take on this goto stuff, if it is not valid C++, it is valid C++.

That logically implies that everything valid C++, which might be overdoing
it a bit ;-)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235

[Bug c++/27235] goto crossing P.O.D. initialization

[gdr at integrable-solutions dot net]

------- Comment #16 from gdr at integrable-solutions dot net  2006-05-01 23:30 -------
Subject: Re:  goto crossing P.O.D. initialization

"falk at debian dot org" <gcc-bugzilla@gcc.gnu.org> writes:

| ------- Comment #15 from falk at debian dot org  2006-05-01 20:55 -------
| (In reply to comment #12)
| > Subject: Re:  goto crossing P.O.D. initialization
| > 
| > "falk at debian dot org" <gcc-bugzilla@gcc.gnu.org> writes:
| > 
| > | I think this is a valid request. While random language extensions aren't
| > | useful,
| > | compatibility with C99 is. Maybe somebody else can comment on this...
| > 
| > You have to be more precise about what you mean by C99 compatibility.
| 
| I have trouble seeing what might be unclear about this term.

I suspect part of the problem is that everybody believes that his/her uses
of the term are so clear that they he/she has trouble seeing anybody
disagree with him/her.

| I mean that code
| that is valid C99 is accepted in C++ unless there is a good reason not to.

And why not the other way around?  I mean, codes that is valid C++ is
accepted in C99 unless there is good reason not to.  As far as I can
see, that also is compatibility.

| just like most of C89 is accepted in C++ unless there is a good reason not
to.

I suspect this is might be one the places things needs to be explained.  

If 

   * only a subset of C89 is valid  C++ and has same meaning as in C++,
   * C99 has carefully departed from both C89 and C++

why is it that "code that is valid C99 is accepted C++ unless there is
a good reason not to"?  

-- Gaby


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27235