Re: Compile-time introspection of free-floating functions, does this work?

   I think I might have come up with a way to detect at runtime if a
free-floating function has been defined or not, and avoid referencing
it if it isn't. More concretely, in a project of mine I need to know
if std::strtold exists in<cstdlib> or not, and call it only if it does
(and if it doesn't, fall back to calling std::strtod).

   What's the jury's opinion of this? Standard, non-standard, ill-formed,
suspicious? Any suggestions to make it better?

//---------------------------------------------------------------------
#include<iostream>
#include<cstdlib>

namespace std
{
     template<typename T1, typename T2>
     char strtold(T1, T2);
}

namespace
{
     const bool hasStrtold =
         (sizeof(std::strtold("0", (char**)0))> 1);

     template<bool> struct Func;

     template<> struct Func<false>
     {
         static void func() { std::cout<< "No strtold().\n"; }
     };

     template<> struct Func<true>
     {
         static void func()
         {
             std::cout<< "Has strtold(). Test:"
                       << std::strtold("12.3", (char**)0)<< "\n";
         }
     };

     void func()
     {
         Func<hasStrtold>::func();
     }
}

int main()
{
     func();
}
//---------------------------------------------------------------------