std::wstring_convert::to_bytes(3)

NAME
std::wstring_convert::to_bytes - std::wstring_convert::to_bytes

Synopsis
   Defined in header <locale>
   byte_string to_bytes( Elem wchar ); (1)
   byte_string to_bytes( const Elem* wptr ); (2)
   byte_string to_bytes( const wide_string& wstr ); (3)
   byte_string to_bytes( const Elem* first, const Elem* last ); (4)
   Performs wide to multibyte conversion, using the codecvt facet supplied at
   construction.
   1) Converts wchar as if it was a string of length 1, to byte_string.
   2) Converts the null-terminated wide character sequence beginning at the wide
   character pointed to by wptr, to byte_string.
   3) Converts the wide string wstr to byte_string.
   4) Converts the wide character sequence [first, last) to byte_string.
   In all cases, the conversion begins in initial shift state, unless non-initial
   starting state was provided to this wstring_convert constructor. The number of
   characters converted and the final value of the conversion state are remembered and
   can be accessed with state() and converted().

Return value
   A byte_string object containing the results of the wide to multibyte conversion. If
   the conversion failed and there was a user-supplied byte-error string provided to
   the constructor of this wstring_convert, returns that byte-error string.

Exceptions
   If this wstring_convert object was constructed without a user-supplied byte-error
   string, throws std::range_error on conversion failure.

Example
// Run this code
 #include <codecvt>
 #include <iomanip>
 #include <iostream>
 #include <locale>
 #include <string>
 // utility function for output
 void hex_print(const std::string& s)
 {
     std::cout << std::hex << std::setfill('0');
     for (unsigned char c : s)
         std::cout << std::setw(2) << static_cast<int>(c) << ' ';
     std::cout << std::dec << '\n';
 }
 int main()
 {
     // wide character data
     std::wstring wstr = L"z\u00df\u6c34\U0001f34c"; // or L"zß水🍌"
     // wide to UTF-8
     std::wstring_convert<std::codecvt_utf8<wchar_t>> conv1;
     std::string u8str = conv1.to_bytes(wstr);
     std::cout << "UTF-8 conversion produced " << u8str.size() << " bytes:\n";
     hex_print(u8str);
     // wide to UTF-16le
     std::wstring_convert<std::codecvt_utf16<wchar_t, 0x10ffff, std::little_endian>> conv2;
     std::string u16str = conv2.to_bytes(wstr);
     std::cout << "UTF-16le conversion produced " << u16str.size() << " bytes:\n";
     hex_print(u16str);
 }

Output:
 UTF-8 conversion produced 10 bytes:
 7a c3 9f e6 b0 b4 f0 9f 8d 8c
 UTF-16le conversion produced 10 bytes:
 7a 00 df 00 34 6c 3c d8 4c df

See also
   from_bytes converts a byte string into a wide string
              (public member function)
   wcsrtombs converts a wide string to narrow multibyte character string, given state
              (function)
   do_out converts a string from InternT to ExternT, such as when writing to file
   [virtual] (virtual protected member function of
              std::codecvt<InternT,ExternT,StateT>)