Pointer to a void * function C++ - c++

Question

I am trying to call pointer to a void * function inside the main method and the compiler is saying assigning to 'funcptr<g>' from incompatible type 'void *(void *). hello function is actually an argument to pthread_create function. That's why it is void * function. How can I create a function pointer to a void * function?
#include <iostream>
#include <pthread.h>
using namespace std;
template<typename T>
using funcptr = void (*T::*)(void *); // I think it is wrong here.
class m {
public:
template <typename T>
struct my_struct {
funcptr<T> ptr;
};
};
class g {
public:
static void *hello(void *);
};
int main() {
struct m::my_struct<g> h;
h.ptr = g::hello; // Error here
return 0;
}

Answer 1

How can I create a function pointer to a void * function?
hello is not a member function, but it's a static function.
So your funcptr should be as follows:
// No template needed.
using funcptr = void* (*)(void *)
Note that hello is declared with static, meaning that it's no longer a member function to g.
Static members of a class are not associated with the objects of the class.
So using void (*T::*)(void *) to cull non-member functions is incorrect.
If you're allowed to use a compiler that supports C++11, you don't even need to manually deduct its type anymore, using decltype:
// decltype deducts its exact type for you.
using funcptr = decltype(&g::hello);
class m
{
public:
struct my_struct
{
funcptr ptr;
};
};
FYI, since hello does not have its definition, you might encounter a linkage error. To prevent that, I assumed that there's some implementation inside:
static void *hello(void *)
{
// Meaningless, but..
return nullptr;
}

Answer 2

if you're using C++11, you can use std::function<> which just bothers about the return type and parameters of the function and not where they are defined and what are its type.
Here is the code using std::function<>
#include <iostream>
#include <functional>
#include <pthread.h>
using namespace std;
class m {
public:
template <typename T>
struct my_struct {
function<void*(void*)> ptr;
};
};
class g {
public:
static void *hello(void *) {
cout<<"Hello.."<<endl;
}
};
int main() {
struct m::my_struct<g> h;
h.ptr = g::hello;
h.ptr(nullptr);
return 0;
}