std::codecvt_utf8_utf16
| Defined in header  <codecvt> | ||
| template< class Elem,           unsigned long Maxcode = 0x10ffff, | (since C++11) (deprecated in C++17) | |
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 | 
[edit] Template Parameters
| Elem | - | either char16_t, char32_t, or wchar_t | 
| Maxcode | - | the largest value of Elemthat 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_utf16facet(public member function) | 
|  (destructor) | destroys a codecvt_utf8_utf16facet(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 type | 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(public member function of std::codecvt) | |
| invokes do_in(public member function of std::codecvt) | |
| invokes do_unshift(public member function of std::codecvt) | |
| invokes do_encoding(public member function of std::codecvt) | |
| invokes do_always_noconv(public member function of std::codecvt) | |
| invokes do_length(public member function of std::codecvt) | |
| invokes do_max_length(public member function of std::codecvt) | 
Protected member functions
| [virtual] | converts a string from internT to externT, such as when writing to file (virtual protected member function of std::codecvt) | 
| [virtual] | converts a string from externT to internT, such as when reading from file (virtual protected member function of std::codecvt) | 
| [virtual] | generates the termination character sequence of externT characters for incomplete conversion (virtual protected member function of std::codecvt) | 
| [virtual] | returns the number of externT characters necessary to produce one internT character, if constant (virtual protected member function of std::codecvt) | 
| [virtual] | tests if the facet encodes an identity conversion for all valid argument values (virtual protected member function of std::codecvt) | 
| [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) | 
| [virtual] | returns the maximum number of externT characters that could be converted into a single internT character (virtual protected member function of std::codecvt) | 
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
#include <iostream> #include <string> #include <codecvt> #include <cassert> #include <locale> int main() { std::string u8 = 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"; for (char16_t c : u16_conv) std::cout << std::hex << std::showbase << 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 << +(unsigned char)c << ' '; }
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 | 
| UCS2 | c16rtomb(without C11's DR488) | codecvt_utf8<char16_t> codecvt_utf8<wchar_t>(Windows) | codecvt_utf16<char16_t> codecvt_utf16<wchar_t>(Windows) | 
| UTF-32 | codecvt<char32_t, char, mbstate_t> | codecvt_utf16<char32_t> | |
| system wide: UTF-32(non-Windows) UCS2(Windows) | mbsrtowcs / wcsrtombs | No | No | 
| converts between character encodings, including UTF-8, UTF-16, UTF-32 (class template) | |
| (C++11)(deprecated in C++17) | tags to alter behavior of the standard codecvt facets (enum) | 
| (C++11)(deprecated in C++17) | converts between UTF-8 and UCS2/UCS4 (class template) | 
| (C++11)(deprecated in C++17) | converts between UTF-16 and UCS2/UCS4 (class template) | 


