Difference between revisions of "cpp/locale/codecvt utf8 utf16"

Revision as of 14:48, 18 April 2013

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Defined in header <codecvt>

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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>;

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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.

Inherited from std::codecvt

Member types

Member name	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,StateT>`) [edit]
in	invokes `do_in` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
unshift	invokes `do_unshift` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
encoding	invokes `do_encoding` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
always_noconv	invokes `do_always_noconv` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
length	invokes `do_length` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
max_length	invokes `do_max_length` (public member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]

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<InternT,ExternT,StateT>`) [edit]
do_in [virtual]	converts a string from `ExternT` to `InternT`, such as when reading from file (virtual protected member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
do_unshift [virtual]	generates the termination character sequence of `ExternT` characters for incomplete conversion (virtual protected member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
do_encoding [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>`) [edit]
do_always_noconv [virtual]	tests if the facet encodes an identity conversion for all valid argument values (virtual protected member function of `std::codecvt<InternT,ExternT,StateT>`) [edit]
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<InternT,ExternT,StateT>`) [edit]
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<InternT,ExternT,StateT>`) [edit]

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

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

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Character conversions
toupper
tolower
String and stream conversions
wstring_convert (C++11/17/26*)
wbuffer_convert (C++11/17/26*)

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> `codecvt_utf8_utf16`<char16_t> `codecvt_utf8_utf16`<char32_t> `codecvt_utf8_utf16`<wchar_t>	N/A
UCS-2	`c16rtomb` (without C11's DR488)	`codecvt_utf8`<char16_t>	`codecvt_utf16`<char16_t>
UTF-32	`mbrtoc32` / `c32rtomb`	`codecvt`<char32_t,char,mbstate_t> `codecvt_utf8`<char32_t>	`codecvt_utf16`<char32_t>
system wchar_t: UTF-32 (non-Windows) UCS-2 (Windows)	`mbsrtowcs` / `wcsrtombs` `use_facet`<`codecvt` <wchar_t,char,mbstate_t>>(`locale`)	`codecvt_utf8`<wchar_t>	`codecvt_utf16`<wchar_t>

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Difference between revisions of "cpp/locale/codecvt utf8 utf16"

Revision as of 14:48, 18 April 2013

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