show usage of extern

explicit-templates/Hund.cpp

@@ -6,12 +6,7 @@ void Hund<FOO>::bar(){
    bellen<FOO>();
 }
 
-template< class FOO>
-void bellen(){
-   std::cout << "wuff" << std::endl;
-}
-
 template class Hund<double>;
-//template void bellen<double>();
+template void bellen<double>();
 
 

explicit-templates/Hund.hpp

 #pragma once
+#include <iostream>
 
 template< class FOO>
 class Hund {
@@ -6,7 +7,9 @@ class Hund {
   void bar();
 };
 
-template <class FOO>
-void bellen();
+template< class FOO>
+void bellen(){
+   std::cout << "wuff" << std::endl;
+}
 
-//extern template void bellen<double>();
\ No newline at end of file
+extern template void bellen<double>();
\ No newline at end of file