declare function pointer in templated class from template arguments

Question

I am trying to declare function pointer from template argument of function prototype

template <typename ReturnType, typename... Args> class DllFunction {
public:
  ReturnType (*fptr_)(Args...);
};

DllFunction<int(int)> f;

but I get this error:

error: C2091: function returns function

Answer 1

You're mixing two different ways.

Or you declare DllFunction receiving the return and the variadic list of argument types

template <typename ReturnType, typename... Args> class DllFunction {
public:
  ReturnType (*fptr_)(Args...);
};

but you have to avoid to call it with the form int(int) and you have to use

// .........VVV  return type
DllFunction<int, int> f;
// ..............^^^  arguments types

or you call using the form ReturnType(Args...) and you have to declare a DllFunction object as follows

template <typename>
class DllFunction;

template <typename ReturnType, typename... Args>
class DllFunction<ReturnType(Args...)> {
public:
  ReturnType (*fptr_)(Args...);
};

You can also use the pointer function form

template <typename>
class DllFunction;

template <typename ReturnType, typename... Args>
class DllFunction<ReturnType(*)(Args...)> {
public:
  ReturnType (*fptr_)(Args...);
};

so you can use decltype() for the template type

int foo (int);

DllFunction<decltype(&foo)> f;