Static data member of a class template (14.5.1.3) Alf and Dietmar are more kind of a 'hack', exploiting that definitions of The suggested answers from Cheers and hth. Thus, according to the standard, it is not allowed. Obviously definitions of static data members of class type are not considered to appear in multiple translations units. Such an entity named D defined in more than one translation unit, then Which some template parameters are not specified (14.7, 14.5.5) in a program provided that each definitionĪppears in a different translation unit, and provided the definitions satisfy the following requirements. Of a class template (14.5.1.3), member function of a class template (14.5.1.1), or template specialization for There can be more than one definition of a class type (Clause 9), enumeration type (7.2), inline function withĮxternal linkage (7.1.2), class template (Clause 14), non-static function template (14.5.6), static data member §3.2.6 and the following paragraphs from the current c++ 17 draft (n4296) define the rules when more than one definition can be present in different translation units:

However, you can define static member functions! Now, at first sight that may not look as if it could help except, of course, that function can have local static variable and returning a reference to one of these behaves nearly like a static member variable: static std::string& bstring(), depending on the order of initialization created by the linker. Since the include guards are only affecting the compilation of one translation unit, they won't help, either. If you put variable definitions into a header, it is going to be defined in each translation unit where the header is included. You can't define a static member variable more than once.

Hpp hack