Is it possible to print a variable's type in standard C++?

Question

For example:

int a = 12;
cout << typeof(a) << endl;

Expected output:

int

Answer 1

Howard Hinnant used magic numbers to extract type name. 康桓瑋 suggested string prefix and suffix. But prefix/suffix keep changing. With “probe_type” type_name automatically calculates prefix and suffix sizes for “probe_type” to extract type name:

#include 
using namespace std;

namespace typeName {
 template 
  constexpr string_view wrapped_type_name () {
#ifdef __clang__
    return __PRETTY_FUNCTION__;
#elif defined(__GNUC__)
    return  __PRETTY_FUNCTION__;
#elif defined(_MSC_VER)
    return  __FUNCSIG__;
#endif
  }

  class probe_type;
  constexpr string_view probe_type_name ("typeName::probe_type");
  constexpr string_view probe_type_name_elaborated ("class typeName::probe_type");
  constexpr string_view probe_type_name_used (wrapped_type_name ().find (probe_type_name_elaborated) != -1 ? probe_type_name_elaborated : probe_type_name);

  constexpr size_t prefix_size () {
    return wrapped_type_name ().find (probe_type_name_used);
  }

  constexpr size_t suffix_size () {
    return wrapped_type_name ().length () - prefix_size () - probe_type_name_used.length ();
  }

  template 
  string_view type_name () {
    constexpr auto type_name = wrapped_type_name ();

    return type_name.substr (prefix_size (), type_name.length () - prefix_size () - suffix_size ());
  }
}

#include 

using typeName::type_name;
using typeName::probe_type;

class test;

int main () {
  cout << type_name () << endl;

  cout << type_name () << endl;
  cout << type_name () << endl;

  const int ic = 42;
  const int* pic = ⁣
  const int*& rpic = pic;
  cout << type_name () << endl;
  cout << type_name () << endl;
  cout << type_name () << endl;

  cout << type_name () << endl;
}

Output

gcc 10.2:

test
const int *&
unsigned int
const int
const int *
const int *&
typeName::probe_type

clang 11.0.0:

test
const int *&
unsigned int
const int
const int *
const int *&
typeName::probe_type

VS 2019 version 16.7.6:

class test
const int*&
unsigned int
const int
const int*
const int*&
class typeName::probe_type