Template typename as type of other parameter of the same template

Question

I would like to create a template, where i can use different vector types, and a constant as the same type of the vector. I would like to able to pass the constant as template parameter in order to let the compiler optimize it, without explicit specialization.

So i tried to re-use the type parameter, but i got illegal type.

#include <vector>
using namespace std;

template<typename WEIGHT, WEIGHT multiplier>
void test_multipier(vector<WEIGHT> &v)
{
    uint16_t num = 16;
    /*...*/
    WEIGHT w = multiplier* (num);
    v.push_back(w);
}

int main()
{
    vector<double> test_vector;

    test_multipier<double,0.01>(test_vector); 
    //^^ Error C2993 'double': illegal type for non-type template parameter 'multiplier'


    return 0;
}

A non-type template parameter cannot be of floating point type. Pass it as a second argument instead. — David G, Oct 01 '15 at 22:14
Duplicate: http://stackoverflow.com/questions/5687540/non-type-template-parameters — Andrey Nasonov, Oct 01 '15 at 22:16

score 2 · Accepted Answer · answered Oct 01 '15 at 22:15

Copied from cppreference.com :

[A non-type template parameter's type] is one of the following types (optionally cv-qualified, the qualifiers are ignored):

std::nullptr_t (since C++11);

integral type;

lvalue reference type (to object or to function);

pointer type (to object or to function);

pointer to member type (to member object or to member function);

enumeration type.

double cannot be used as a non-type template parameter.

Template typename as type of other parameter of the same template

1 Answers1