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std::codecvt_utf8_utf16

From cppreference.com

< cpp‎ | locale

Defined in header `<codecvt>`
template< class Elem, unsigned long Maxcode = 0x10ffff, std::codecvt_mode Mode = (std::codecvt_mode)0 > class codecvt_utf8_utf16 : public std::codecvt<Elem, char, std::mbstate_t>;		(since C++11) (deprecated in C++17) (removed in C++26)

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.

Contents

1 Template Parameters
2 Member functions
3 std::codecvt_utf8_utf16::codecvt_utf8_utf16
- 3.1 Parameters
4 std::codecvt_utf8_utf16::~codecvt_utf8_utf16
5 Inherited from std::codecvt
6 Inherited from std::codecvt_base
- 6.1 Example
- 6.2 See also

[edit] 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

[edit] 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

out	invokes `do_out` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
in	invokes `do_in` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
unshift	invokes `do_unshift` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
encoding	invokes `do_encoding` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
always_noconv	invokes `do_always_noconv` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
length	invokes `do_length` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
max_length	invokes `do_max_length` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]

Protected member functions

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

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

[edit] 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

[edit] See also

Character conversions	locale-defined multibyte (UTF-8, GB18030)	UTF-8	UTF-16
UTF-16	`mbrtoc16` / `c16rtomb` (with C11's DR488)	`codecvt`<char16_t,char,mbstate_t> `codecvt_utf8_utf16`<char16_t> `codecvt_utf8_utf16`<char32_t> `codecvt_utf8_utf16`<wchar_t>	N/A
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_utf8`<char32_t>	`codecvt_utf16`<char32_t>
system wchar_t: UTF-32 (non-Windows) UCS-2 (Windows)	`mbsrtowcs` / `wcsrtombs` `use_facet`<`codecvt` <wchar_t,char,mbstate_t>>(`locale`)	`codecvt_utf8`<wchar_t>	`codecvt_utf16`<wchar_t>

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

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