NAME¶

std::codecvt_utf8_utf16 - std::codecvt_utf8_utf16

Synopsis¶

Defined in header <codecvt>
template<

class Elem, (since C++11)
unsigned long Maxcode = 0x10ffff, (deprecated in C++17)
std::codecvt_mode Mode = (std::codecvt_mode)0 > (removed in C++26)
class codecvt_utf8_utf16

: public std::codecvt<Elem, char, std::mbstate_t>;

std::codecvt_utf8_utf16 is a std::codecvt facet which encapsulates conversion
between a UTF-8 encoded byte string and UTF-16 encoded character string. If Elem is
a 32-bit type, one UTF-16 code unit will be stored in each 32-bit character of the
output sequence.

This is an N:M conversion facet, and cannot be used with std::basic_filebuf (which
only permits 1:N conversions, such as UTF-32/UTF-8, between the internal and the
external encodings). This facet can be used with std::wstring_convert.

Template Parameters¶

Elem - either char16_t, char32_t, or wchar_t
Maxcode - the largest value of Elem that this facet will read or write without error
Mode - a constant of type std::codecvt_mode

Member functions¶

constructor constructs a new codecvt_utf8_utf16 facet
(public member function)
destructor destroys a codecvt_utf8_utf16 facet
(public member function)

std::codecvt_utf8_utf16::codecvt_utf8_utf16

explicit codecvt_utf8_utf16( std::size_t refs = 0 );

Constructs a new std::codecvt_utf8_utf16 facet, passes the initial reference counter
refs to the base class.

Parameters¶

refs - the number of references that link to the facet

std::codecvt_utf8_utf16::~codecvt_utf8_utf16

~codecvt_utf8_utf16();

Destroys the facet. Unlike the locale-managed facets, this facet's destructor is
public.

Inherited from std::codecvt

Member types¶

Member name Definition
intern_type internT
extern_type externT
state_type stateT

Member objects¶

Member name Type
id (static) std::locale::id

Member functions¶

invokes do_out
out (public member function of std::codecvt<InternT,ExternT,StateT>)

invokes do_in
in (public member function of std::codecvt<InternT,ExternT,StateT>)

invokes do_unshift
unshift (public member function of std::codecvt<InternT,ExternT,StateT>)

invokes do_encoding
encoding (public member function of std::codecvt<InternT,ExternT,StateT>)

invokes do_always_noconv
always_noconv (public member function of std::codecvt<InternT,ExternT,StateT>)

invokes do_length
length (public member function of std::codecvt<InternT,ExternT,StateT>)

invokes do_max_length
max_length (public member function of std::codecvt<InternT,ExternT,StateT>)

Protected member functions¶

converts a string from InternT to ExternT, such as when writing to
do_out file
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)
converts a string from ExternT to InternT, such as when reading
do_in from file
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)
generates the termination character sequence of ExternT characters
do_unshift for incomplete conversion
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)
returns the number of ExternT characters necessary to produce one
do_encoding InternT character, if constant
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)
tests if the facet encodes an identity conversion for all valid
do_always_noconv argument values
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)
calculates the length of the ExternT string that would be consumed
do_length by conversion into given InternT buffer
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)
returns the maximum number of ExternT characters that could be
do_max_length converted into a single InternT character
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>)

Inherited from std::codecvt_base

Member type Definition
enum result { ok, partial, error, noconv }; Unscoped enumeration type

Enumeration constant Definition
ok conversion was completed with no error
partial not all source characters were converted
error encountered an invalid character
noconv no conversion required, input and output types are the same

Example¶

// Run this code

#include <cassert>
#include <codecvt>
#include <cstdint>
#include <iostream>
#include <locale>
#include <string>

int main()
{
std::string u8 = "z\u00df\u6c34\U0001f34c";
std::u16string u16 = u"z\u00df\u6c34\U0001f34c";

// UTF-8 to UTF-16/char16_t
std::u16string u16_conv = std::wstring_convert<
std::codecvt_utf8_utf16<char16_t>, char16_t>{}.from_bytes(u8);
assert(u16 == u16_conv);
std::cout << "UTF-8 to UTF-16 conversion produced " << u16_conv.size()
<< " code units:\n" << std::showbase << std::hex;
for (char16_t c : u16_conv)
std::cout << static_cast<std::uint16_t>(c) << ' ';

// UTF-16/char16_t to UTF-8
std::string u8_conv = std::wstring_convert<
std::codecvt_utf8_utf16<char16_t>, char16_t>{}.to_bytes(u16);
assert(u8 == u8_conv);
std::cout << "\nUTF-16 to UTF-8 conversion produced "
<< std::dec << u8_conv.size() << " bytes:\n" << std::hex;
for (char c : u8_conv)
std::cout << +static_cast<unsigned char>(c) << ' ';
std::cout << '\n';
}

Output:¶

UTF-8 to UTF-16 conversion produced 5 code units:
0x7a 0xdf 0x6c34 0xd83c 0xdf4c
UTF-16 to UTF-8 conversion produced 10 bytes:
0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c

See also¶

Character locale-defined multibyte UTF-8 UTF-16
conversions (UTF-8, GB18030)
codecvt<char16_t,char,mbstate_t>
UTF-16 mbrtoc16 / c16rtomb (with C11's codecvt_utf8_utf16<char16_t> N/A
DR488) codecvt_utf8_utf16<char32_t>
codecvt_utf8_utf16<wchar_t>
UCS-2 c16rtomb (without C11's DR488) codecvt_utf8<char16_t> codecvt_utf16<char16_t>
UTF-32 mbrtoc32 / c32rtomb codecvt<char32_t,char,mbstate_t> codecvt_utf16<char32_t>
codecvt_utf8<char32_t>
system
wchar_t:
mbsrtowcs / wcsrtombs
UTF-32 use_facet<codecvt codecvt_utf8<wchar_t> codecvt_utf16<wchar_t> (non-Windows) <wchar_t,char,mbstate_t>>(locale)
UCS-2
(Windows)

converts between character encodings, including UTF-8, UTF-16,
codecvt UTF-32
(class template)
codecvt_mode
(C++11) tags to alter behavior of the standard codecvt facets
(deprecated in C++17) (enum)
(removed in C++26)
codecvt_utf8
(C++11) converts between UTF-8 and UCS-2/UCS-4
(deprecated in C++17) (class template)
(removed in C++26)
codecvt_utf16
(C++11) converts between UTF-16 and UCS-2/UCS-4
(deprecated in C++17) (class template)
(removed in C++26)