How to unfold a template to string when the possible type be float or string?

In C++, i want to build a string only container from a template.

For example:

template<typename T>
void show(const T & t) {  // the T can be map<string, string> or <string, float> or <string, int>
  std::unordered_map<std::string, std::string> r;
  for (const auto & i : t) {
     const auto & j = i.first;
     const auto & k = i.second;  //  TODO: how to
     // make k as string, possible type of k can be 
     // int float or string???
     // put them into r
  }
  return r;
}

How can i implement this?