[Bug libstdc++/54388] [4.7/4.8 Regression] std::array.at() const results in undefined behaviour

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54388

--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-09-09 
17:56:15 UTC ---
(In reply to comment #10)
> Can the compiler warn about the original (buggy) code?

It already does:

c.cc: In function ‘A& get(int)’:
c.cc:3:43: error: invalid initialization of non-const reference of type ‘A&’
from an rvalue of type ‘A’
 A& get(int i) { return i == 0 ? a : throw 1; }
                                           ^
But warnings are suppressed in system headers.

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-09-09 
17:56:56 UTC ---
Author: redi
Date: Sun Sep  9 17:56:51 2012
New Revision: 191114

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191114
Log:
    PR libstdc++/54388
    * include/std/array (array::at() const): Ensure lvalue result.
    * testsuite/23_containers/array/element_access/54388.cc: New.
    * testsuite/23_containers/array/tuple_interface/get_neg.cc: Adjust
    dg-error line numbers.
    * testsuite/23_containers/array/tuple_interface/tuple_element_neg.cc:
    Likewise.

Added:
    trunk/libstdc++-v3/testsuite/23_containers/array/element_access/54388.cc
      - copied, changed from r191113,
trunk/libstdc++-v3/testsuite/23_containers/array/tuple_interface/tuple_element_neg.cc
Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/std/array
    trunk/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
   
trunk/libstdc++-v3/testsuite/23_containers/array/tuple_interface/tuple_element_neg.cc