User defined literal arguments are not constexpr?

Question

I\'m testing out user defined literals. I want to make _fac return the factorial of the number.

Having it call a constexpr function works,

Answer 1

@Pubby. The easy way to digest the char non-type parameter pack is to cature it into an initializer list for a string. Then you can use atoi, atof, etc:

#include 

template
  int
  operator "" _suffix()
  {
    const char str[]{Chars..., '\0'};
    return atoi(str);
  }

int
main()
{
  std::cout << 12345_suffix << std::endl;
}

Remember to tack on a null character for the C-style functions.