How do I pass a function as a parameter

Win 7 cygwin gcc 4.8.3 -std=gnu++11

I've researched this on stackoverflow and cplusplus and thought that I'd passed a function as a parameter correctly, even 'elegantly', but it's clear I have misunderstood something. Can anyone explain how to pass a function as an argument correctly, and why what I have won't work?

A single warning is given for the prototype and a single error for the invocation. Changing genX to genY in the comments but both genX and genY have the same warnings/errors.

class MyClass {
   typedef double (*func_t)(double sum);
   void driver();
   double genX(func_t fnc) { };  
   double genY(double (*funct)(double sum)) { };
   // note: no known conversion for argument 1 from 
   // '<unresolved overloaded function type>' to 
   // MyClass::func_t {aka double (*)(double)}
   double myThingie(double sum) { };
};

void MyClass::driver() {
   genX(myThingie);
   genY(myThingie);
   // no matching function for call to 'MyClass::genX(<unresolved overloaded function type>)'
}