[Bug c++/19809] New: Multiple definitions of friend functions in template classes

["sstrasser at systemhaus-gruppe dot de" <gcc-bugzilla at gcc dot gnu dot org>]

This report is based on <16899453.0502060835.6c893401@posting.google.com>

given this testcase:

#include <iostream>
template<int i>
struct n{
  friend void foo(){
    std::cerr << i << std::endl;;
  }
};

int main(){
  n<1> n1;
  n<2> n2;
  n<3> n3;
  foo();
}

there must be a bug here, though I'm not sure what exactly it is.

a) it could be a multiple definition of foo, which is reported by version 3.3.4,
but not by 4.0.0 and 3.4.3.

b) std note 14.5.3.3 could mean that it's not a multiple definition:

<<<3 When a function is defined in a friend function declaration in a class
template, the function is defined when the class template is first instantiated.
The function is defined even if it is never used.>>>

so if it's _only_ defined on the first instantiation this is not a multiple
definition - but then I don't think it is legal to use the template arguments of
struct n in the function definition

c) even if b) is wrong and usage of template arguments is allowed, there's still
a bug, because the result of the testcase above is "3", so the _last_
instantiation is used.


comeau C++ chooses a), so does 3.3.4.

-- 
           Summary: Multiple definitions of friend functions in template
                    classes
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sstrasser at systemhaus-gruppe dot de
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19809