arg_count.cpp

#include <iostream>

template<typename Ret, typename... Args>
constexpr int arg_count(Ret(*)(Args...)){
  return sizeof...(Args);
}


void foo(int, float, double, char){}
int foo2(float, int, char*){return 0;}
void foo3(){}

int main(){
    std::cout << arg_count(foo) << std::endl; // 4
    std::cout << arg_count(foo2) << std::endl;// 3
    std::cout << arg_count(foo3) << std::endl;// 0
 
 return 0;
}