How to check if object is const or not?

Question

My problem is that I have no idea how to check if object is const. I can only use C++98. How can I check if object have const modifier? How to overload functions properly?

int main(){
  Vec x;
  const Vec y;

  cout<<"Is x const? ";
  y.IfConst(x);     // cout << "no"
  cout<<"\n";

  cout<<"Is x const? ";
  x.IfConst(x)      // cout << "no"
  cout<<"\n";

  cout<<"Is y const? ";
  x.IfConst(y);     // cout << "yes"
  cout<<"\n";

  cout<<"Is y const? ";
  y.IfConst(y);     // cout << "yes"
  cout<<"\n";
  /**/
}

I need output look like: is x const? no is x const? no is y const? yes is y const? yes

I used:

void Vec::IsConst(Vec const &vecc) const{
  std::cout << "YES" << std::endl;      
}

void Vec::IsConst(Vec const &vecc) {
  std::cout << "NO" << std::endl;       
}

Answer 1

constness is known and used only as compile time, the information doesn't exist at runtime, it has no sense.

However, at compile time, if you have a C++11 compliant compiler, you can use the standard std::is_const type trait on a type:

int main() 
{
    std::cout << std::boolalpha;
    std::cout << std::is_const<const int>::value << '\n';
    std::cout << std::is_const<Vec>::value  << '\n';
}

If you don't have a c++11 compiler, you can use boost one.

Answer 2

Your proposed syntax does not make sense to me.

This works for me.

#include <iostream>

template <typename T> bool isConst(T& x)
{
   return false;
}

template <typename T> bool isConst(T const& x)
{
   return true;
}

int main() 
{
   int x;
   const double y = 0.0;

   std::cout << "Is x const? ";
   std::cout << isConst(x) << "\n";

   std::cout << "Is y const? ";
   std::cout << isConst(y) << "\n";
}

Output:

Is x const? 0
Is y const? 1