How well are `char16_t` and `char_32_t` supported in c++11?

The following code works as expected. The source code, file "file.txt" and "out.txt" are all encoded with utf8. But it does not compile when I change wchar_t to char16_t or char32_t at the first line in main(). I've tried both gcc5.4 and clang8.0 with -std=c++11. My goal is to replace wchar_t with char16_t, as wchar_t takes twice space in RAM. I thought these 3 types are equally well supported in c++11 and later standards. What do I miss here?

#include<iostream>
#include<fstream>
#include<locale>
#include<codecvt>
#include<string>

int main(){
  typedef wchar_t my_char;

  std::locale::global(std::locale("en_US.UTF-8"));

  std::ofstream out("file.txt");
  out << "123正则表达式abc" << std::endl;
  out.close();

  std::basic_ifstream<my_char> win("file.txt");
  std::basic_string<my_char> wstr;
  win >> wstr;
  win.close();

  std::ifstream in("file.txt");
  std::string str;
  in >> str;
  in.close();

  std::wstring_convert<std::codecvt_utf8<my_char>, my_char> my_char_conv;
  std::basic_string<my_char> conv = my_char_conv.from_bytes(str);

  std::cout << (wstr == conv ? "true" : "false") << std::endl;

  std::basic_ofstream<my_char> wout("out.txt");
  wout << wstr << std::endl << conv << std::endl;
  wout.close();

  return 0;
}