std::codecvt_utf8_utf16
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String and stream conversions Unicode conversion facets C library locales
(C++11/17/26*)
(C++11/17/26*)
(C++11/17/26*)
(C++11/17/26*)
codecvt_utf8_utf16
(C++11/17/26*)
(C++11/17/26*)
Defined in header
<codecvt>
template<
(since C++11) class Elem,
unsigned long Maxcode = 0x10ffff,
std::codecvt_mode Mode = (std::codecvt_mode )0 >
class codecvt_utf8_utf16
(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
[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)
codecvt_utf8_utf16 facet (public member function)
(destructor)
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
Nested types
Type
Definition
intern_type
internT
extern_type
externT
state_type
stateT
[edit] Data members
Member
Description
Member functions
Protected member functions
[virtual]
InternT to ExternT, such as when writing to file (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
[virtual]
ExternT to InternT, such as when reading from file (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
[virtual]
ExternT characters for incomplete conversion (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
[virtual]
ExternT characters necessary to produce one InternT character, if constant (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
[virtual]
(virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
[virtual]
ExternT string that would be consumed by conversion into given InternT buffer (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
[virtual]
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
Nested 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] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2229 | C++98 | the constructor and destructor were not specified | specifies them |
[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> |
N/A |
| UCS-2 | c16rtomb (without C11's DR488) | codecvt_utf8 <char16_t> | codecvt_utf16 <char16_t> |
| UTF-32 |
codecvt <char32_t,char,mbstate_t> |
codecvt_utf16 <char32_t> | |
| system wchar_t:
UTF-32 (non-Windows) |
mbsrtowcs / wcsrtombs |
codecvt_utf8 <wchar_t> | codecvt_utf16 <wchar_t> |
(C++11)(deprecated in C++17)(removed in C++26)
(enum) [edit]
(C++11)(deprecated in C++17)(removed in C++26)
(class template) [edit]
(C++11)(deprecated in C++17)(removed in C++26)
(class template) [edit]