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From: "daniel.kruegler at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/52476] [C++11] Unordered multimap reorders equivalent elements
Date: Sun, 04 Mar 2012 16:11:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D52476

--- Comment #2 from Daniel Kr=C3=BCgler <daniel.kruegler at googlemail dot =
com> 2012-03-04 16:10:19 UTC ---
(In reply to comment #1)
> (we should double check that by avoiding any use of
> fancy C++11 features like initializer lists in the testcase)

I rewrote the testcase in C++03 form and based on TR1 unordered map:

//------
#include <tr1/unordered_map>
#include <iostream>
#include <utility>

typedef std::tr1::unordered_multimap<int, int> map_type;

void printHashTable(const map_type& map)
{
  for (unsigned i =3D 0; i < map.bucket_count(); ++i) {
    std::cout << "b[" << i << "]:" << std::endl;
    for (map_type::const_local_iterator it =3D map.begin(i); it !=3D map.en=
d(i);
++it) {
      std::cout << "   " << map.hash_function()(it->first) << " ["
                << it->first << "," << it->second << "]" << std::endl;
    }
  }
  std::cout << "----------------------" << std::endl;
}

int main()
{
  typedef std::pair<int, int> P;
  const P input1[] =3D {
    P(0,0),
    P(1,0),
    P(2,0),
    P(3,0),
    P(4,0),
    P(1,1)
  };
  map_type dict(input1, input1 + sizeof(input1)/sizeof(input1[0]));
  printHashTable(dict);

  const P input2[] =3D {
    P(3,1),
    P(3,2),
    P(5,0)
  };
  dict.insert(input2, input2 + sizeof(input2)/sizeof(input2[0]));
  printHashTable(dict);

  dict.max_load_factor(0.5);
  printHashTable(dict);
}
//------

The incorrect runtime behaviour is unchanged compared to the original form.
This means, one could actually remove the [C++11] tag from the bug title.