[Bug c/37231] New: GCC does not compile code with label statements that are followed by a declaration

[Bug c/37231] New: GCC does not compile code with label statements that are followed by a declaration

[colding at 42tools dot com]

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Hi,

The following simple code does not build using GCC 3.3 or 4.x:

###### main.c ########
int
main(int argc, char *argv[])
{
        goto out;
out:
        int retv = 0;
        return retv;
}
#######################

GCC tells me:

####### GCC output ########
main.c: In function ‘main’:
main.c:7: error: syntax error before ‘int’
main.c:8: error: ‘retv’ undeclared (first use in this function)
main.c:8: error: (Each undeclared identifier is reported only once
main.c:8: error: for each function it appears in.)
###########################

I'm not aware that the above code should be invalid so I think this is a
compiler bug. Putting a ';' after the label will make the code compile just
fine:

###### working main.c ########
int
main(int argc, char *argv[])
{
        goto out;
out: ;
        int retv = 0;
        return retv;
}
##############################

Best regards,
  jules


-- 
           Summary: GCC does not compile code with label statements that are
                    followed by a declaration
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: colding at 42tools dot com
  GCC host triplet: i686-apple-darwin9


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[paolo dot carlini at oracle dot com]

------- Comment #1 from paolo dot carlini at oracle dot com  2008-08-25 10:43 -------
I think the improved error message in mainline makes clear this is invalid (the
EDG front-end agrees, by the way):

37231.c:6: error: a label can only be part of a statement and a declaration is
not a statement

And the "work-around" is indeed Ok.


-- 

paolo dot carlini at oracle dot com changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[manu at gcc dot gnu dot org]

------- Comment #2 from manu at gcc dot gnu dot org  2008-08-25 18:55 -------
I think this was fixed already in GCC 4.3.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[aapo dot rantalainen at gmail dot com]

------- Comment #3 from aapo dot rantalainen at gmail dot com  2009-07-08 19:36 -------
Above code doesn't compile:
int main(int argc, char *argv[])
{
  int a=1;
  switch (a)
    {
    case 1:
    int b=2;
    break;
    }
return 0;
}

Error "a label can only be part of a statement and a declaration is not a
statement"

Same workaround:  add ; before int b=2;

gcc -v
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.3.3-5ubuntu4'
--with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.3
--program-suffix=-4.3 --enable-clocale=gnu --enable-libstdcxx-debug
--enable-objc-gc --enable-mpfr --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.3.3 (Ubuntu 4.3.3-5ubuntu4)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2009-07-08 19:42 -------
(In reply to comment #3)
> Above code doesn't compile:

Yes it should not be compile.  The error message has been improved to tell you
what the problem is (that is what Manu was saying in his comment #2).


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[manu at gcc dot gnu dot org]

------- Comment #5 from manu at gcc dot gnu dot org  2009-07-08 21:34 -------
(In reply to comment #4)
> (In reply to comment #3)
> > Above code doesn't compile:
> 
> Yes it should not be compile.  The error message has been improved to tell you
> what the problem is (that is what Manu was saying in his comment #2).

Indeed.

Aapo, what is difficult to understand from the the current error message? I
would like to improve it as much as possible.


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |aapo dot rantalainen at
                   |                            |gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[manu at gcc dot gnu dot org]

------- Comment #6 from manu at gcc dot gnu dot org  2009-07-09 09:25 -------
Is this mandated to be an error by the standard? Perhaps GCC could just pedwarn
and add the ';' itself, and compile just fine.

Otherwise, I might add a hint:

note: either add ';' or open a block after the label.

Thoughts?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[alex dot pyattaev at gmail dot com]

------- Comment #7 from alex dot pyattaev at gmail dot com  2010-05-09 10:29 -------
I have encountered the bug with switch construct. And the problem is not the
error message, but the fact that it is still compiling just fine this code:
switch (chan_prop.model_type)
        {
                case CM_STATIC:
                        return static_channel_model(src, ntransmitters, dst,
                                                    &chan_prop);
                case CM_FRISS:
                        return friss_channel_model(src, ntransmitters, dst,
                                                   &chan_prop);
                default:
                        return -1;
        }
There should be some consistency at least! I'd like to see this fixed properly.
The compiler should be perfectly predictable, and not like "Sorry, i don't like
this construct here... put a semicolon please".

I'd like this bug to be reopened and FIXED PROPERLY

gcc --version =  (Gentoo 4.4.3-r2 p1.2) 4.4.3


-- 

alex dot pyattaev at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |alex dot pyattaev at gmail
                   |                            |dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[manu at gcc dot gnu dot org]

------- Comment #8 from manu at gcc dot gnu dot org  2010-05-09 15:26 -------
(In reply to comment #7)
> There should be some consistency at least! I'd like to see this fixed properly.
> The compiler should be perfectly predictable, and not like "Sorry, i don't like

It is predictable: a label can only be part of a statement and a declaration is
not a statement.  Now "return x;" is a statement, so it compiles fine.  This is
mandated by the C standard, it is not the compiler's decision. Does it work
different with any other compiler?

Please, tell us what is difficult to understand in the error message and how
could it be better explained.

On the other hand, I don't know whether if GCC adds an empty statement before
the declaration and just emits a warning with -pedantic, then it still complies
with the C standard. I don't have time to investigate this, sorry.


> this construct here... put a semicolon please".
> 
> I'd like this bug to be reopened and FIXED PROPERLY
> 
> gcc --version =  (Gentoo 4.4.3-r2 p1.2) 4.4.3
> 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[alex dot pyattaev at gmail dot com]

------- Comment #9 from alex dot pyattaev at gmail dot com  2010-05-09 19:07 -------
(In reply to comment #7)
> I have encountered the bug with switch construct. And the problem is not the
> error message, but the fact that it is still compiling just fine this code:
> switch (chan_prop.model_type)
>         {
>                 case CM_STATIC:
>                         return static_channel_model(src, ntransmitters, dst,
>                                                     &chan_prop);
>                 case CM_FRISS:
>                         return friss_channel_model(src, ntransmitters, dst,
>                                                    &chan_prop);
>                 default:
>                         return -1;
>         }
> There should be some consistency at least! I'd like to see this fixed properly.
> The compiler should be perfectly predictable, and not like "Sorry, i don't like
> this construct here... put a semicolon please".
> 
> I'd like this bug to be reopened and FIXED PROPERLY
> 
> gcc --version =  (Gentoo 4.4.3-r2 p1.2) 4.4.3
> 

A good example of seemingly normal code is following:
 switch (whatever)
        {
                case 1:
                        int i=0;
                        i++;
                        printf("%d",i);                   
                        break;
        }
It is technically perfectly legal to declare i as a local variable. However,
the compiler issues an error. And it is absolutely not clear why "int i=0;" is
not a statement. That is probably the only really annoying case. Moving
declaration of i into a code block solves the issue. I spent like 10 minutes
trying to find out why perfectly legal code would not compile.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[dougsemler at gmail dot com]

------- Comment #10 from dougsemler at gmail dot com  2010-05-09 23:25 -------
(In reply to comment #9)
> 
> A good example of seemingly normal code is following:
>  switch (whatever)
>         {
>                 case 1:
>                         int i=0;
>                         i++;
>                         printf("%d",i);                   
>                         break;
>         }
> It is technically perfectly legal to declare i as a local variable. However,
> the compiler issues an error. And it is absolutely not clear why "int i=0;" is
> not a statement. That is probably the only really annoying case. Moving
> declaration of i into a code block solves the issue. I spent like 10 minutes
> trying to find out why perfectly legal code would not compile.
> 

Not to beat a dead horse here but...

Because that is *not* perfectly legal C code, and will not be valid C++ code if
you add another case label after it (jump over initialization)?  A declaration
("int i") is not a statement.

That fails on both MSVC and gcc.  In fact, MSVC will still barf even after
adding a semicolon after the label to make it a statement. (MSVC error is
"error 2143: missing ';' before type")


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231

[Bug c/37231] GCC does not compile code with label statements that are followed by a declaration

[alex dot pyattaev at gmail dot com]

------- Comment #11 from alex dot pyattaev at gmail dot com  2010-05-09 23:29 -------
(In reply to comment #10)
> (In reply to comment #9)
> > 
> > A good example of seemingly normal code is following:
> >  switch (whatever)
> >         {
> >                 case 1:
> >                         int i=0;
> >                         i++;
> >                         printf("%d",i);                   
> >                         break;
> >         }
> > It is technically perfectly legal to declare i as a local variable. However,
> > the compiler issues an error. And it is absolutely not clear why "int i=0;" is
> > not a statement. That is probably the only really annoying case. Moving
> > declaration of i into a code block solves the issue. I spent like 10 minutes
> > trying to find out why perfectly legal code would not compile.
> > 
> 
> Not to beat a dead horse here but...
> 
> Because that is *not* perfectly legal C code, and will not be valid C++ code if
> you add another case label after it (jump over initialization)?  A declaration
> ("int i") is not a statement.
> 
> That fails on both MSVC and gcc.  In fact, MSVC will still barf even after
> adding a semicolon after the label to make it a statement. (MSVC error is
> "error 2143: missing ';' before type")
> 
Ok, lets have pity for dead horse. Let it be as it is=)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37231