CODEWITHSUNDEEP
c++templates
lezebulon
lezebulon

Reputation: 7994

Find template parameters at runtime

it's possible to have access to template "type", for instance in the std

std::vector<int>::size_type

is it possible to have the same thing for objects passed as template parameters? For instance:

template<int i>
class A {
//?
};

A<3> instance;
int number = instance::???? //<--- assigns 3 to number

is it possible to get the 3 passed in the object type again at runtime? Without creating a specific member in the A class (which would increase the size of the object)

thanks

Upvotes: 3

Views: 430

Answers (2)

perreal
perreal

Reputation: 97938

template<int i>
class A { 
public:
  enum { number = i };
};

int main() {
  A<3> instance;
  std::cout << instance.number;
  return 0;
}

Upvotes: 2

Mark Ransom
Mark Ransom

Reputation: 308121

The type of the variable is known to the compiler at compile time, it's just a matter of getting it to give it up.

template<int i>
int get(const A<i> & instance)
{
    return i;
}

Upvotes: 5

Related Questions