How to create method which works only with predefined types in C++?

Question

I need to create such an overloaded operator, which works only with predefined types (e.g. works with ofstream, stringstream, but doesn't work with ostream & iostream) . Here is an example:

// Possible usage: class Test : public BinaryTemplate  -  now you can simply write&read class Test from/to a file

class BinaryTemplate
{
public:
    template <typename K>
    // friend std::ostream& operator << (std::ostream&, K const&); // LINKER ERROR 2019
    friend std::ios& operator << (std::ios&, K const&); // OK
}

template <typename Stream, typename K>
Stream& operator << (Stream& out, K const& c)
{
    out.write(reinterpret_cast<const char*>(&c), sizeof(K));
    out.flush();
    return out;
}

BinaryTemplate bt;
cout << bt; // LINKER ERROR 2019 or OK

The compiler's behavior is very strange ( I hope it's clear for understanding according to commented errors). When I declare friend method like <ios> it's OK, because cout object is instance of ostream, which is derived from ios. But when I declare friend method like <ostream> it causes LINKER ERROR, but cout object is instance of ostream, then it is very strange for LINKER ERROR to be caused. So, my question is:

Why Linker has such a behavior and how should I create class method, which works only with predefined types?

Thanks a lot