c++ - static template member variable has internal linkage but is not defined -

Yes, I know, there is a question with almost the same title, but it refers to a different situation. Error message) In my case, I have a .cpp file with a big named designation name (implementation details). There is a property class template with a static data member in that name space, which I need to access from outside the unknown namespace. I give it a little bit of meat:

  file.hpp namespace Bar {template & lt; Typename A & gt; Struct foo {static_assert (is_same & lt; a, float & gt; :: value} is_same & lt; a, double>: value, ""); Fixed zero set_static_var (a const & x); // ...}; }   
 and  
  file.cpp namespace {template & lt; Typename A & gt; Struct foo_traits {// supports the implementation of several static code bars: foo & lt; & Gt; Fixed A data; }; The template's & lt; & Gt; Float foo_traits & lt; Float & gt; :: datum; // No change if this is in the global namespace template & lt; & Gt; Double foo_traits & lt; Double & gt; :: datum; Template structure foo_traits & lt; Float & gt; Template structure foo_traits & lt; Double> } Namespace bar {template  // error only appears if these rows are present template structure foo & lt; float & gt; // But without these lines, the whole file is zero. }   
 and I have the variable  foo_traits & lt; & Gt; :: Error found on DataM  (and later linkage failure).  Note  I use  clang ++ -std = c ++ 11 -stdlib = libc ++  (version 3.3), which is  only < / Em> produces a warning, but (as I have said) in my real application is a support failure of the warning (the said symbols are remembered properly). Not a compiler warning with GCC, though. Maybe this is a lie bug?  End note   
 What is the correct way to define those variables? Note that declaring them out of the names of anonymous names will not be compiled. Also keep in mind that, APIs are manufactured with a simple non-template.  
  Note  How do I prevent this problem from being obstructed (which I can think of myself), but how it is done correctly.   
 
 
 I think the right solution is simply:  
  namespace {Template & lt; Typename A & gt; Struct foo_traits {// supports the implementation of several static code bars: foo & lt; & Gt; Fixed A data; }; Template & lt; typename A & gt; A Fu_trats & lt; A & gt; :: datum; }   
 
 The problem with your code, AFAICT, is that  
  float fu_trit & lt; Float & gt; :: datum;   
  foo_traits  refers to the expertise that does not exist.  
 See.