std::codecvt_utf16
<codecvt>
class Elem,
unsigned long Maxcode = 0x10ffff,
std::codecvt_mode Mode = (std::codecvt_mode )0 >
class codecvt_utf16
(deprecated in C++17)
(removed in C++26)
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 std::codecvt facet can be used to read and write UTF-16 files in binary mode.
UCS-2 is an archaic encoding that is a subset of UTF-16, which encodes scalar values in the range U+0000-U+FFFF (Basic Multilingual Plane) only.
Contents
[edit] Template Parameters
Elem that this facet will read or write without error
[edit] Member functions
codecvt_utf16 facet (public member function)
codecvt_utf16 facet (public member function)
std::codecvt_utf16::codecvt_utf16
Constructs a new std::codecvt_utf16 facet, passes the initial reference counter refs to the base class.
Parameters
std::codecvt_utf16::~codecvt_utf16
Destroys the facet. Unlike the locale-managed facets, this facet's destructor is public.
Inherited from std::codecvt
Nested types
intern_type
internT
extern_type
externT
state_type
stateT
[edit] Data members
Member functions
Protected member functions
InternT to ExternT, such as when writing to file (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
ExternT to InternT, such as when reading from file (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
ExternT characters for incomplete conversion (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
ExternT characters necessary to produce one InternT character, if constant (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
(virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
ExternT string that would be consumed by conversion into given InternT buffer (virtual protected member function of
std::codecvt<InternT,ExternT,StateT>) [edit]
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
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] Notes
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.
[edit] Example
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
[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> |
(enum) [edit]
(class template) [edit]
(class template) [edit]