Defined in header <codecvt> | ||
|---|---|---|
template<
class Elem,
unsigned long Maxcode = 0x10ffff,
std::codecvt_mode Mode = (std::codecvt_mode)0
> class codecvt_utf16 : public std::codecvt<Elem, char, std::mbstate_t>;
| (since C++11) (deprecated in C++17) |
std::codecvt_utf16 is a std::codecvt facet which encapsulates conversion between a UTF-16 encoded byte string and UCS-2 or UTF-32 character string (depending on the type of Elem). This codecvt facet can be used to read and write UTF-16 files in binary mode.
| UCS-2 is the same encoding as UTF-16, except that it encodes scalar values in the range U+0000-U+FFFF (Basic Multilingual Plane) only. | (since C++23) |
| 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 |
| (constructor) | constructs a new codecvt_utf16 facet (public member function) |
| (destructor) | destroys a codecvt_utf16 facet (public member function) |
explicit codecvt_utf16( std::size_t refs = 0 ); |
Constructs a new std::codecvt_utf16 facet, passes the initial reference counter refs to the base class.
| refs | - | the number of references that link to the facet |
~codecvt_utf16(); |
Destroys the facet. Unlike the locale-managed facets, this facet's destructor is public.
| Member type | Definition |
|---|---|
intern_type | internT |
extern_type | externT |
state_type | stateT |
| Member name | Type |
|---|---|
id (static) | std::locale::id |
invokes do_out (public member function of std::codecvt<InternT,ExternT,StateT>) |
|
invokes do_in (public member function of std::codecvt<InternT,ExternT,StateT>) |
|
invokes do_unshift (public member function of std::codecvt<InternT,ExternT,StateT>) |
|
invokes do_encoding (public member function of std::codecvt<InternT,ExternT,StateT>) |
|
invokes do_always_noconv (public member function of std::codecvt<InternT,ExternT,StateT>) |
|
invokes do_length (public member function of std::codecvt<InternT,ExternT,StateT>) |
|
invokes do_max_length (public member function of std::codecvt<InternT,ExternT,StateT>) |
|
[virtual] | converts a string from InternT to ExternT, such as when writing to file (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) |
|
[virtual] | converts a string from ExternT to InternT, such as when reading from file (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) |
|
[virtual] | generates the termination character sequence of ExternT characters for incomplete conversion (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) |
|
[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>) |
|
[virtual] | tests if the facet encodes an identity conversion for all valid argument values (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) |
|
[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>) |
|
[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>) |
| 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 |
Although the standard requires that this facet works with UCS-2 when the size of Elem is 16 bits, some implementations use UTF-16 instead, making this a non-converting locale. The term "UCS-2" was deprecated and removed from ISO 10646.
Since C++23, UCS-2 does not refer to its original definition anymore. It becomes a synonym of UTF-16, but with a smaller encoding range.
The following example demonstrates decoding of UTF-16le file on a system with 32-bit wchar_t. On a system with 16-bit wchar_t, decoding of the third character will fail because std::codecvt_utf16<char16_t> produces UCS-2, not UTF-16.
#include <codecvt>
#include <cwchar>
#include <fstream>
#include <iostream>
#include <locale>
#include <string>
void prepare_file()
{
// UTF-16le data (if host system is little-endian)
char16_t utf16le[4] = {0x007a, // latin small letter 'z' U+007a
0x6c34, // CJK ideograph "water" U+6c34
0xd834, 0xdd0b}; // musical sign segno U+1d10b
// store in a file
std::ofstream fout("text.txt");
fout.write(reinterpret_cast<char*>(utf16le), sizeof utf16le);
}
int main()
{
prepare_file();
// open as a byte stream
std::wifstream fin("text.txt", std::ios::binary);
// apply facet
fin.imbue(std::locale(fin.getloc(),
new std::codecvt_utf16<wchar_t, 0x10ffff, std::little_endian>));
wchar_t c = 0;
for (std::cout << std::showbase << std::hex; fin.get(c);
std::cout << static_cast<std::wint_t>(c) << '\n');
}Output:
0x7a 0x6c34 0x1d10b
| Character conversions | locale-defined multibyte (UTF-8, GB18030) | UTF-8 | UTF-16 |
|---|---|---|---|
| UTF-16 |
mbrtoc16 / c16rtomb (with C11's DR488) |
| N/A |
| UCS-2 |
c16rtomb (without C11's DR488) |
codecvt_utf8<char16_t> |
codecvt_utf16<char16_t> |
| UTF-32 |
|
|
|
| system wchar_t: UTF-32 (non-Windows) |
|
codecvt_utf8<wchar_t> |
codecvt_utf16<wchar_t> |
| 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 UCS-2/UCS-4 (class template) |
|
(C++11)(deprecated in C++17) | converts between UTF-8 and UTF-16 (class template) |
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