Re: Multiple definition and specialization of static data member
Wu Yongwei wrote:
I posted the following message days ago to comp.std.c++, and got an
helpful answer from Alberto Ganesh Barbati. However, I would like to
hear more comments from you gurus here, esp. whether the behaviour of
MSVC 8 is standard conforming, best with quotations from the Standard.
-------------------------------
I encountered a problem in a header file like the following:
template <typename DataType>
class FMC
{
public:
static DataType Epsilon;
private:
FMC() {}
};
template <typename DataType>
DataType FMC<DataType>::Epsilon = static_cast<DataType>(0.000001);
template <>
double FMC<double>::Epsilon = static_cast<double>(0.0000000001);
When multiple .cpp files include this header file, GCC 3.4.4 (or some
earlier version) will complain:
...: multiple definition of `FMC<double>::Epsilon'
...
Static data members of class templates are an exempt from One
Definition Rule [3.2/5], this is why you can define the static member
in the header file without getting a multiple definitions error.
OTOH, full specialization is not a template so that the exempt does not
apply here, this is why you get the error when you put the full
specialization of the static member in the header.
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
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