Question

Suppose I have following template class:

template<unsigned char I, unsigned char F>
class FOO
{
  ....
}

In the main function, I have many such variables, with different (I, F), like following,

int main()
{
   .....
   FOO<4, 2> a;
   FOO<6, 3> b;
   ......
}

I want to retain the value of I or F for the defined variables in my main function. Of course, I can define a public/private members for FOO and save the value of (I, F) inside the FOO’s constructor, like

template<I,F>
FOO<I,F>::FOO(){
   i = I;
   f = F;
}

Disadvantage of this method is obvious: It enlarge the size of the FOO. IMO, (I, F) of any variable can be determined at compiling time, so there should be a way to do this without creating local variable.

Answer 1

The usual way (like std::array in C++11) is to do the following:

constexpr unsigned char i() const { return I; }
constexpr unsigned char f() const { return F; }

If your compiler doesn’t support constexpr, remove it.