#include <iostream>

#include <fstream>

#include <string>

#include <locale>

#include <iomanip>

#include <string>

#include <codecvt>

using namespace std;

// utility wrapper to adapt locale-bound facets for wstring/wbuffer convert

template<class Facet>

struct deletable_facet : Facet

{

template<class ...Args>

deletable_facet(Args&& ...args) : Facet(forward<Args>(args)...)

{}

~deletable_facet()

{}

};

int main()

{

// UTF-8 narrow multibyte encoding

string data = u8"z\u00df\u6c34\U0001f34c";

// or u8"zß水🍌"

// or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9f\x8d\x8c";

ofstream("text.txt") << data;

// using system-supplied locale's codecvt facet

wifstream fin("text.txt");

// reading from wifstream will use codecvt<wchar_t, char, mbstate_t>

// this locale's codecvt converts UTF-8 to UCS4 (on systems such as Linux)

fin.imbue(locale("en_US.UTF-8"));

cout << "The UTF-8 file contains the following UCS4 code points: \n";

for (wchar_t c; fin >> c; )

cout << "U+" << hex << setw(4) << setfill('0') << c << '\n';

// using standard (locale-independent) codecvt facet

wstring_convert<

deletable_facet<codecvt<char16_t, char, mbstate_t>>, char16_t> conv16;

u16string str16 = conv16.from_bytes(data);

cout << "The UTF-8 file contains the following UTF-16 code points: \n";

for (char16_t c : str16)

cout << "U+" << hex << setw(4) << setfill('0') << c << '\n';

}