Why is a C++ template accepting an array not more specialized than one accepting a pointer according to GCC 5.3 and Clang 4.0?

Question

Why are the next two template declarations ambiguous (so neither is more specialized than the other)? I know this question has been raised many times on Stack Overflow, but usua

Answer 1

The template declarations are not ambiguous; the following code compiles and runs OK:

#include <iostream>
#include <string>

using namespace std;

template<class T>
void func(char* buf, T size) {cout<<"void func(char*,T)\n";}
template<size_t N>
void func(char (&buf)[N], std::size_t size) {
  cout<<"void func(char (&)[],size_t)\n";}

int main() {
  char buf[3];
  func(buf, 2);
  func<3>(buf, 2);
  func(reinterpret_cast<char (&)[3]>(buf), 2);
  //next is ambiguous
  //func(reinterpret_cast<char (&)[3]>(buf), size_t(2));
  func<3>(reinterpret_cast<char (&)[3]>(buf), size_t(2));
  return 0;
}

However, the commented-out call is ambiguous. To disambiguate it use:

func<3>(reinterpret_cast<char (&)[3]>(buf), size_t(2));

This works OK and calls the correct function.