Get the type of a variable (C++17)

tell_me_the_type.cpp

// This file is a "Hello, world!" in C++ language by GCC for wandbox.
#include <iostream>
#include <cstdlib>

// https://stackoverflow.com/questions/81870/is-it-possible-to-print-a-variables-type-in-standard-c

template <class T>
constexpr
std::string_view
type_name()
{
    using namespace std;
#ifdef __clang__
    string_view p = __PRETTY_FUNCTION__;
    return string_view(p.data() + 34, p.size() - 34 - 1);
#elif defined(__GNUC__)
    string_view p = __PRETTY_FUNCTION__;
#  if __cplusplus < 201402
    return string_view(p.data() + 36, p.size() - 36 - 1);
#  else
    return string_view(p.data() + 49, p.find(';', 49) - 49);
#  endif
#elif defined(_MSC_VER)
    string_view p = __FUNCSIG__;
    return string_view(p.data() + 84, p.size() - 84 - 7);
#endif
}

int main()
{
    std::cout << "Hello, Wandbox!" << std::endl;
    int (*(*foo[5])(char(*)()))[3];
    std::cout << "decltype(foo) is " << type_name<decltype(foo)>() << '\n';
}

// GCC reference:
//   https://gcc.gnu.org/

// C++ language references:
//   https://msdn.microsoft.com/library/3bstk3k5.aspx
//   http://www.cplusplus.com/
//   https://isocpp.org/
//   http://www.open-std.org/jtc1/sc22/wg21/

// Boost libraries references:
//   http://www.boost.org/doc/