Testing template based class with const template parameter which has to be varied

Question

I am developing a template based library to support fixed point integers and I came up with this class and now I have to test it for various values of INT_BITS and FRAC_BITS. but since they are const (and they have to be so for a reason), I am unable to initialize objects with variable INT_BITS in a loop and hence it is making testing this library very difficult.

template<int INT_BITS, int FRAC_BITS>
struct fp_int
{
     public:
            static const int BIT_LENGTH = INT_BITS + FRAC_BITS;
            static const int FRAC_BITS_LENGTH = FRAC_BITS;
     private:
            // Value of the Fixed Point Integer 
            ValueType stored_val;
};

I tried a lot of tricks mentioned here , here and here. I tried using a std::vector of const int and const_cast but nothing seems to work.

I was wondering that that how do you test such libraries where the template parameter is a const for a large test values ?

Answer 1

You can simulate a for loop using template meta programming.

#include <iostream>

typedef int ValueType;

template<int INT_BITS, int FRAC_BITS>
struct fp_int
{
   public:
      static const int BIT_LENGTH = INT_BITS + FRAC_BITS;
      static const int FRAC_BITS_LENGTH = FRAC_BITS;
   private:
      // Value of the Fixed Point Integer 
      ValueType stored_val = 0;
};

template <unsigned int N> struct ForLoop
{
   static void testFpInt()
   {
      std::cout << "Testing fp_int<" << N << ", 2>\n";
      fp_int<N, 2> x;
      // Use x

      // Call the next level
      ForLoop<N-1>::testFpInt();
   }
};

// Terminating struct.
template <> struct ForLoop<0>
{
   static void testFpInt()
   {
      std::cout << "Testing fp_int<" << 0 << ", 2>\n";
      fp_int<0, 2> x;
      // Use x
   }
};

int main()
{
   ForLoop<10>::testFpInt();
   return 0;
}

Output

Testing fp_int<10, 2>
Testing fp_int<9, 2>
Testing fp_int<8, 2>
Testing fp_int<7, 2>
Testing fp_int<6, 2>
Testing fp_int<5, 2>
Testing fp_int<4, 2>
Testing fp_int<3, 2>
Testing fp_int<2, 2>
Testing fp_int<1, 2>
Testing fp_int<0, 2>

You can find more information on the web by searching for "for loop using template metaprogramming".