Calling static function pointer from static method

Question

I have the following code in my Individual.hpp file:

typedef string (Individual::*getMethodName)(void);    
static getMethodName currentFitnessMethodName;
static string getCurrentFitnessMethodName();

And this on my .cpp file:

string Individual::getCurrentFitnessMethodName(){
    return (Individual::*currentFitnessMethodName)();
}

I'm using function pointers in other parts of my code but always in the same object context, so I do (this->*thingyMajigger)(params), but with that static call I get the following error:

Expected unqualified-id

I have tried multiple permutations of said code but none seem to work. Can anyone share some light?

Cheers

Being a pointer to non-static member function, currentFitnessMethodName requires an Individual object to be called on. In your static function getCurrentFitnessMethodName, there is no this pointer. Do you have another Individual object you can use there? — aschepler
– aschepler, Commented Jun 9, 2017 at 21:51
Why are you using static and function pointer instead of just doing it correctly with object.method? — stark
– stark, Commented Jun 9, 2017 at 22:14
@aschepler, no I don't. I just described that as an example. — Yan Mendes
– Yan Mendes, Commented Jun 9, 2017 at 22:59
@stark because the value of that pointer is variable depending on certain params. And since the point is not needing the object to use this function, I can't do that — Yan Mendes
– Yan Mendes, Commented Jun 9, 2017 at 23:02

Qix - MONICA WAS MISTREATED · Accepted Answer · 2017-06-09 23:11:59Z

Your typedef is what's messing you up. Static methods are just regular functions that just happen to have access to protected/private static members of their class.

Change the typedef to simply:

typedef string (*getMethodName)(void);

The former syntax is for non-static member methods.

As an example, the following doesn't compile:

#include <iostream>
#include <string>

using namespace std;
class Foo {
public:
    typedef string (Foo::*staticMethod)();

    static staticMethod current;

    static string ohaiWorld() {
        return "Ohai, world!";
    }

    static string helloWorld() {
        return "Hello, world!";
    }

    static string callCurrent() {
        return Foo::current();
    }
};

Foo::staticMethod Foo::current = &Foo::ohaiWorld;

int main() {
    cout << Foo::callCurrent() << endl;
    Foo::current = &Foo::helloWorld;
    cout << Foo::callCurrent() << endl;
    return 0;
}

But changing the typedef from

typedef string (Foo::*staticMethod)();

to

typedef string (*staticMethod)();

allows it to compile - and as expected it outputs:

Ohai, world!
Hello, world!

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