How to Define and Initialize Static Data Members in C Class Templates?

Defining Static Data Member in a Class Template

A need often arises to define a static data member within a class template. However, the traditional approach of defining the member within the class declaration is not feasible as it must be initialized outside the class definition due to non-integral data types. This poses a challenge, especially when the class is a template, prohibiting the definition from being placed in a separate compiled file.

To resolve this issue, a technique involves defining the static data member within the header file but initializing it outside in a separate definition. Here's an example:

template <typename T>
struct S
{
    static double something_relevant;
};

template <typename T>
double S<T>::something_relevant = 1.5;

In this approach, the static data member something_relevant is initially declared within the class template definition. Then, its initialization is performed outside in a separate definition, where it can be any non-integral data type. Since the definition is part of the template, the compiler ensures it is defined only once, avoiding multiple definitions.

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