[Bug c/31977] New: can return OK from "int main()" without a return statement by using a goto before the return

[Bug c/31977] New: can return OK from "int main()" without a return statement by using a goto before the return

[bmcfadden at cdp dot com]

I'm using gcc 3.4.5, and I was looking into a weird condition.  The following
program compiles OK:

#include <stdio.h>
int alloc()
{
return 0;
}
int main(int argc, char* argv[])
{
       printf("Testing!\n");
       if(alloc() == 0)goto Radhe;
       return 0;
Radhe:
         printf("Hello\n");
}

The result is a program which prints "Testing", then "Hello", and then exits. 
I and a few other people expect that the compiler would generate an error
during compile, because main should return an int, and not all code paths have
a return statement; however, both gcc and msvc are compiling this OK.

added note: this bug was recently discussed on the NTDEV mailing list.


-- 
           Summary: can return OK from "int main()" without a return
                    statement by using a goto before the return
           Product: gcc
           Version: 3.4.5
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bmcfadden at cdp dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31977

[Bug c/31977] can return OK from "int main()" without a return statement by using a goto before the return

[bmcfadden at cdp dot com]

------- Comment #1 from bmcfadden at cdp dot com  2007-05-17 16:48 -------
Created an attachment (id=13571)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13571&action=view)
The file from -save-temps


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31977

[Bug c/31977] can return OK from "int main()" without a return statement by using a goto before the return

[bmcfadden at cdp dot com]

------- Comment #2 from bmcfadden at cdp dot com  2007-05-17 16:52 -------
Created an attachment (id=13572)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=13572&action=view)
the assembly (.s) file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31977

[Bug c/31977] can return OK from "int main()" without a return statement by using a goto before the return

[bmcfadden at cdp dot com]

------- Comment #3 from bmcfadden at cdp dot com  2007-05-17 16:54 -------
Reading specs from /usr/lib/gcc/i386-redhat-linux/3.4.5/specs
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --enable-shared --enable-threads=posix
--disable-checking --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-java-awt=gtk --host=i386-redhat-linux
Thread model: posix
gcc version 3.4.5 20051201 (Red Hat 3.4.5-2)


-- 

bmcfadden at cdp dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bmcfadden at cdp dot com
   GCC host triplet|                            |i386-redhat-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31977

[Bug c/31977] can return OK from "int main()" without a return statement by using a goto before the return

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2007-05-17 18:53 -------
[pinskia-laptop:~/src] pinskia% gcc -Wreturn-type t.c
t.c: In function 'main':
t.c:15: warning: control reaches end of non-void function


This code is only undefined at runtime which means you cannot error out.


-- 

pinskia at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31977

[Bug c/31977] can return OK from "int main()" without a return statement by using a goto before the return

[bangerth at dealii dot org]

------- Comment #5 from bangerth at dealii dot org  2007-05-17 20:38 -------
Both the C99 standard (section 5.1.2.2.3) and the C++ standard (3.6.1/5)
say that if you hit the end of the main() function, then this is equivalent
to a "return 0;" statement.

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at dealii dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31977

[Bug c/31977] can return OK from "int main()" without a return statement by using a goto before the return

[pinskia at gcc dot gnu dot org]

------- Comment #6 from pinskia at gcc dot gnu dot org  2007-05-17 20:45 -------
(In reply to comment #5)
> Both the C99 standard (section 5.1.2.2.3) and the C++ standard (3.6.1/5)
> say that if you hit the end of the main() function, then this is equivalent
> to a "return 0;" statement.

C90 is different from both of those and it is just undefined behavior there.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31977