[Bug c++/26512] g++ doesn't recognize user-defined operator<<(ostream, const pair<int, double> &)

["bangerth at dealii dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #11 from bangerth at dealii dot org  2006-03-08 04:49 -------
This is indeed invalid under the present rules:
---------------
typedef std::map<int, double> M;
namespace std {
extern std::ostream &operator <<(std::ostream &f, const M::value_type &p);
};

void f()
{
        M m;
        std::copy(m.begin(), m.end(),
                  std::ostream_iterator<M::value_type>(std::cout));
}
---------------
When inside std::copy, the compiler needs to lookup an operator<< for
its arguments. It does so in the present namespace (i.e. std::) as well
as the namespaces of all arguments. The arguments are std::ofstream and
std::pair (and possibly the template arguments of two classes, though
I'm not sure about that). All these arguments are from namespace std::
or are builtin types that have no associated namespace. Lookup therefore
has to fail.

The solution is to put your own definition of operator<< into namespace
std:: -- not pretty, but a solution that we have discussed several times
here in this database...

W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at dealii dot org
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26512