NAME¶

std::codecvt_utf16 - std::codecvt_utf16

Synopsis¶

Defined in header <codecvt>
template< class Elem,

unsigned long Maxcode = 0x10ffff, (since C++11)
std::codecvt_mode Mode = (std::codecvt_mode)0 > (deprecated in C++17)

class codecvt_utf16 : public std::codecvt<Elem, char,
std::mbstate_t>;

std::codecvt_utf16 is a std::codecvt facet which encapsulates conversion between a
UTF-16 encoded byte string and UCS2 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.

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

Member functions¶

constructor constructs a new codecvt_utf16 facet
(public member function)
destructor destroys a codecvt_utf16 facet
(public member function)

std::codecvt_utf16::codecvt_utf16

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.

Parameters¶

refs - the number of references that link to the facet

std::codecvt_utf16::~codecvt_utf16

~codecvt_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¶

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

Protected member functions¶

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

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

Notes¶

Although the standard requires that this facet works with UCS2 when the size of Elem
is 16 bits, some implementations use UTF-16 instead, making this a non-converting
locale. The term "UCS2" was deprecated and removed from the Unicode standard.

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 UCS2, not UTF-16.

// Run this code

#include <fstream>
#include <iostream>
#include <string>
#include <locale>
#include <codecvt>

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>));

for (wchar_t c; fin.get(c); )
std::cout << std::showbase << std::hex << c << '\n';
}

Output:¶

0x7a
0x6c34
0x1d10b

See also¶

Character locale-defined
conversions multibyte UTF-8 UTF-16
(UTF-8, GB18030)
mbrtoc16 / codecvt<char16_t, char, mbstate_t>
UTF-16 c16rtomb(with C11's codecvt_utf8_utf16<char16_t> N/A
DR488) codecvt_utf8_utf16<char32_t>
codecvt_utf8_utf16<wchar_t>
c16rtomb(without codecvt_utf8<char16_t> codecvt_utf16<char16_t>
UCS2 C11's DR488)
codecvt_utf8<wchar_t>(Windows) codecvt_utf16<wchar_t>(Windows)
codecvt<char32_t, char, mbstate_t> codecvt_utf16<char32_t>
UTF-32 mbrtoc32 / c32rtomb codecvt_utf8<char32_t> codecvt_utf16<wchar_t>(non-Windows)
codecvt_utf8<wchar_t>(non-Windows)
mbsrtowcs /
system wide: wcsrtombs UTF-32(non-Windows) use_facet<codecvt No No
UCS2(Windows) <wchar_t, char,
mbstate_t>>(locale)

converts between character encodings, including UTF-8,
codecvt UTF-16, UTF-32
(class template)
codecvt_mode tags to alter behavior of the standard codecvt facets
(C++11)(deprecated in C++17) (enum)
codecvt_utf8 converts between UTF-8 and UCS2/UCS4
(C++11)(deprecated in C++17) (class template)
codecvt_utf8_utf16 converts between UTF-8 and UTF-16
(C++11)(deprecated in C++17) (class template)