[Bug c++/63388] New: cout of enum class value - segmentation fault

[Bug c++/63388] New: cout of enum class value - segmentation fault

[kuq03132 at qoika dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63388

            Bug ID: 63388
           Summary: cout of enum class value - segmentation fault
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kuq03132 at qoika dot com

See example:

//==go.cpp============================================

#include <iostream>

enum class Month {jan=1, feb, mar, apr, may, jun, jul, aug, sep, oct, nov,
dec};

std::ostream& operator<<(std::ostream& os, Month m)
{
  return os << m;                    // BUG - SEGMENTATION FAULT
}


int main()
{
  Month m = Month::may;
  std::cout << m << '\n';
  return 0;
}

//====================================================



Compiled and run with:

c++ -std=c++11 -o go go.cpp
./go 
Segmentation fault



DON'T WE WANT a COMPILER ERROR INSTEAD?
(Segfaulting with something so "simple" is very dangerous!)
(Problem also if -std=c++14)


To get the code to work correctly, we can convert the Month m to int:
int(m)


std::ostream& operator<<(std::ostream& os, Month m)
{
  return os << int(m);      // CONVERT TO INT - ok
}

Thanks.
A.

PS: Thanks for the gnu c++ compiler. I know I say "simple" above. But I'm not
fooled. A c++ compiler is a complex monster.

[Bug c++/63388] cout of enum class value - segmentation fault

[kuq03132 at qoika dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63388

--- Comment #1 from kuq03132 at qoika dot com ---
(problem might be in libstdc++)

[Bug c++/63388] cout of enum class value - segmentation fault

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63388

Andreas Schwab <schwab@linux-m68k.org> changed:

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

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> ---
Endless recursion, os << m is calling operator<<(std::ostream&,Month).

[Bug c++/63388] cout of enum class value - segmentation fault

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63388

Marc Glisse <glisse at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic
           Severity|major                       |normal

--- Comment #3 from Marc Glisse <glisse at gcc dot gnu.org> ---
I guess it would be possible to have an optional warning, late in the
optimization process, when we see an empty infinite loop:

  <bb 3>:
  goto <bb 3>;

I don't know how many false positives we would get from that, but the
limitation to an empty block might make them rare enough.