std::codecvt_utf8_utf16

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< cpp‎ | locale

Defined in header `<codecvt>`
template< class Elem, unsigned long Maxcode = 0x10ffff, std::codecvt_mode Mode = (std::codecvt_mode)0 > class codecvt_utf8_utf16 : public std::codecvt<Elem, char, std::mbstate_t>;

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 codepoint will be stored in each 32-bit character of the output sequence. This codecvt facet can be used to read and write UTF-8 files, both text and binary.

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)	constructs a new `codecvt_utf8_utf16` facet (public member function)
(destructor)	destroys a `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

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 reading a UTF-8 file into a UTF-16 string on a system with 32-bit wchar_t

Run this code

#include <fstream>
#include <iostream>
#include <string>
#include <locale>
#include <codecvt>
 
int main()
{
    std::ofstream("text.txt") << u8"z\u6c34\U0001d10b";
 
    std::wifstream file1("text.txt");
    file1.imbue(std::locale("en_US.UTF8"));
    std::cout << "Normal read from file (using default UTF-8/UTF-32 codecvt)\n";
    for (wchar_t c; file1 >> c; )
        std::cout << std::hex << std::showbase << c << '\n';
 
    std::wifstream file2("text.txt");
    file2.imbue(std::locale(file2.getloc(), new std::codecvt_utf8_utf16<wchar_t>));
    std::cout << "UTF-16 read from the same file (using codecvt_utf8_utf16)\n";
    for (wchar_t c; file2 >> c; )
        std::cout << std::hex << std::showbase << c << '\n';
}

Output:

Normal read from file (using default UTF-8/UTF-32 codecvt)
0x7a
0x6c34
0x1d10b
UTF-16 read from the same file (using codecvt_utf8_utf16)
0x7a
0x6c34
0xd834
0xdd0b

[edit] See also

Character conversions	narrow multibyte (char)	UTF-8 (char)	UTF-16 (char16_t)
UTF-16	`mbrtoc16`(one way)	`codecvt`<char16_t, char, mbstate_t> `codecvt_utf8_utf16`<char16_t> `codecvt_utf8_utf16`<char32_t> `codecvt_utf8_utf16`<wchar_t>	N/A
UCS2	`c16rtomb`(one way)	`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_utf16 (C++11)	converts between UTF-16 and UCS2/UCS4 (class template)

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