std::codecvt_utf8

#include <codecvt>
#include <cstdint>
#include <iostream>
#include <locale>
#include <string>
 
int main()
{
 // UTF-8 data. The character U+1d10b, musical sign segno, does not fit in UCS-2
 std::string utf8 = "z\u6c34\U0001d10b";
 
 // the UTF-8 / UTF-16 standard conversion facet
 std::wstring_convert <std::codecvt_utf8_utf16 <char16_t>, char16_t> utf16conv;
 std::u16string utf16 = utf16conv.from_bytes(utf8);
 std::cout << "UTF-16 conversion produced " << utf16.size() << " code units:\n"
 << std::showbase << std::hex ;
 for (char16_t c : utf16)
 std::cout << static_cast<std::uint16_t >(c) << ' ';
 
 // the UTF-8 / UCS-2 standard conversion facet
 std::wstring_convert <std::codecvt_utf8<char16_t>, char16_t> ucs2conv;
 try
 {
 std::u16string ucs2 = ucs2conv.from_bytes(utf8);
 }
 catch(const std::range_error & e)
 {
 std::u16string ucs2 = ucs2conv.from_bytes(utf8.substr(0, ucs2conv.converted()));
 std::cout << "\nUCS-2 failed after producing " << std::dec << ucs2.size()
 << " characters:\n" << std::showbase << std::hex ;
 for (char16_t c : ucs2)
 std::cout << static_cast<std::uint16_t >(c) << ' ';
 std::cout << '\n';
 }
}

UTF-16 conversion produced 4 code units:
0x7a 0x6c34 0xd834 0xdd0b
UCS-2 failed after producing 2 characters:
0x7a 0x6c34