std::codecvt_utf16

From cppreference.com

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>;;

std::codecvt_utf16 is a std::codecvt facet which encapsulates conversion between a UTF-16 encoded byte string and UCS2 or UCS4 character string (depending on the type of Elem). This codecvt facet can be used to read and write UTF-16 files in binary mode.

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`)

in	invokes `do_in` (public member function of `std::codecvt`)

unshift	invokes `do_unshift` (public member function of `std::codecvt`)

encoding	invokes `do_encoding` (public member function of `std::codecvt`)

always_noconv	invokes `do_always_noconv` (public member function of `std::codecvt`)

length	invokes `do_length` (public member function of `std::codecvt`)

max_length	invokes `do_max_length` (public member function of `std::codecvt`)

Protected member functions


do_out [virtual]	converts a string from internT to externT, such as when writing to file (virtual protected member function of `std::codecvt`)

do_in [virtual]	converts a string from externT to internT, such as when reading from file (virtual protected member function of `std::codecvt`)

do_unshift [virtual]	generates the termination character sequence of externT characters for incomplete conversion (virtual protected member function of `std::codecvt`)

do_encoding [virtual]	returns the number of externT characters necessary to produce one internT character, if constant (virtual protected member function of `std::codecvt`)

do_always_noconv [virtual]	tests if the facet encodes an identity conversion for all valid argument values (virtual protected member function of `std::codecvt`)

do_length [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`)

do_max_length [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

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

[edit] See also

Character conversions	narrow multibyte (char)	UTF-8 (char)	UTF-16 (char16_t)
UTF-16	`mbrtoc16` / `c16rtomb`	`codecvt`<char16_t, char, mbstate_t> `codecvt_utf8_utf16`<char16_t> `codecvt_utf8_utf16`<char32_t> `codecvt_utf8_utf16`<wchar_t>	N/A
UCS2	No	`codecvt_utf8`<char16_t>	`codecvt_utf16`<char16_t>
UTF-32/UCS4 (char32_t)	`mbrtoc32` / `c32rtomb`	`codecvt`<char32_t, char, mbstate_t> `codecvt_utf8`<char32_t>	`codecvt_utf16`<char32_t>
UCS2/UCS4 (wchar_t)	No	`codecvt_utf8`<wchar_t>	`codecvt_utf16`<wchar_t>
wide (wchar_t)	`codecvt`<wchar_t, char, mbstate_t> `mbsrtowcs` / `wcsrtombs`	No	No


codecvt	converts between character encodings, including UTF-8, UTF-16, UTF-32 (class template)

codecvt_mode (C++11)	tags to alter behavior of the standard codecvt facets (enum)

codecvt_utf8 (C++11)	converts between UTF-8 and UCS2/UCS4 (class template)

codecvt_utf8_utf16 (C++11)	converts between UTF-8 and UTF-16 (class template)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)