[Bug c++/30680] New: Spurious "might be used uninitialized" warning in STL use.

["hartog at best dot ms dot philips dot com" <gcc-bugzilla at gcc dot gnu dot org>]

/*
Spurious "might be used uninitialized" warning in STL use.
The following short program produces a spurious warning.
The quoted function in stl_uninitialized.h is
  template<typename _InputIterator, typename _ForwardIterator>
    inline _ForwardIterator
    __uninitialized_copy_aux(_InputIterator __first, _InputIterator __last,
                             _ForwardIterator __result,
                             __false_type)
    {
      _ForwardIterator __cur = __result;    // this is line 82
      try
        {
          for ( ; __first != __last; ++__first, ++__cur)
            std::_Construct(&*__cur, *__first);
          return __cur;
        }
      catch(...)
        {
          std::_Destroy(__result, __cur);
          __throw_exception_again;
        }
    }

We see this warning in other circumstances on several gcc versions,
always in STL headers and usually in very simple statements of the 
form "sometype a = b;" where 'a' is reported a uninitialized (sic!).

The sample given here compiles without warnings with -O1, but 
this is not generally the case.

Any solutions or work-arounds?
*/
#include <iostream>
#include <ostream>
#include "boost/format.hpp"

int main()
{
    std::cout << boost::format("0x%04x ") % 42 << std::endl;
}

/*
$ uname -a
CYGWIN_NT-5.1  1.5.24(0.156/4/2) 2007-01-31 10:57 i686 Cygwin
$ gcc --version
gcc (GCC) 3.4.4 (cygming special, gdc 0.12, using dmd 0.125)

$ g++ -ansi -Wall -O2 -I/cygdrive/d/Info/boost_1_32_0/ simpleformat.cpp
  /usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_uninitialized.h: 
  In member function 
    `void std::vector<_Tp, _Alloc>::_M_fill_insert(
      __gnu_cxx::__normal_iterator<typename _Alloc::pointer, std::vector<_Tp,
_Alloc> >, 
      size_t, const _Tp&)
   [with _Tp = boost::io::detail::format_item<char, std::char_traits<char>,
std::allocator<char> >, 
      _Alloc = std::allocator<boost::io::detail::format_item<char,
std::char_traits<char>, 
     std::allocator<char> > >]':
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_uninitialized.h:82: 
  warning: '__cur' might be used uninitialized in this function
/usr/lib/gcc/i686-pc-cygwin/3.4.4/include/c++/bits/stl_uninitialized.h:82: 
  warning: '__cur' might be used uninitialized in this function
*/


-- 
           Summary: Spurious "might be used uninitialized" warning in STL
                    use.
           Product: gcc
           Version: 3.4.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: hartog at best dot ms dot philips dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30680