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std::codecvt_utf8

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template< class Elem, unsigned long Maxcode = 0x10ffff, std::codecvt_mode Mode = (std::codecvt_mode)0 > class codecvt_utf8 : public std::codecvt<Elem, char, std::mbstate_t>;
std::codecvt_utf8 std::codecvt , UTF-8 UCS2 UCS4 ( Elem). codecvt UTF-8 , , .
:
std::codecvt_utf8 is a std::codecvt facet which encapsulates conversion between a UTF-8 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-8 files, both text and binary.
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Elem
char16_t, char32_t, wchar_t
:
either char16_t, char32_t, or wchar_t
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Maxcode
Elem,
:
the largest value of Elem that this facet will read or write without error
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Mode
std::codecvt_mode
:
a constant of type std::codecvt_mode
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std::codecvt

Member types

intern_type internT
extern_type externT
state_type stateT

Member objects

:
Member name
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 Type
id () std::locale::id

Member functions
do_out
:
invokes do_out
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(public - std::codecvt) []
do_in
:
invokes do_in
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(public - std::codecvt) []
do_unshift
:
invokes do_unshift
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(public - std::codecvt) []
do_encoding
:
invokes do_encoding
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(public - std::codecvt) []
do_always_noconv
:
invokes do_always_noconv
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(public - std::codecvt) []
do_length
:
invokes do_length
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(public - std::codecvt) []
do_max_length
:
invokes do_max_length
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(public - std::codecvt) []

Protected member functions

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


std::codecvt_base

enum result { ok, partial, error, noconv };
:
Unscoped enumeration type
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:
Enumeration constant
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 Definition
ok
:
conversion was completed with no error
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partial
:
not all source characters were converted
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error
:
encountered an invalid character
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noconv
,
:
no conversion required, input and output types are the same
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UCS2/UTF-8 UTF-16/UTF-8 : UCS2 .
:
The following example demonstrates the difference between UCS2/UTF-8 and UTF-16/UTF-8 conversions: the third character in the string is not a valid UCS2 character.
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#include <iostream>
#include <string>
#include <locale>
#include <codecvt>
int main()
{
    // UTF-8 data. The character U+1d10b, musical sign segno, does not fit in UCS2
    std::string utf8 = u8"z\u6c34\U0001d10b";

    // the UTF-8 / UTF-16 standard conversion facet
    std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> utf16conv;
    std::u16string utf16 = utf16conv.from_bytes(utf8);
    std::cout << "UTF16 conversion produced " << utf16.size() << " code points:\n";
    for(char16_t c : utf16)
        std::cout << std::hex << std::showbase << c << '\n';

    // the UTF-8 / UCS2 standard conversion facet
    std::wstring_convert<std::codecvt_utf8<char16_t>, char16_t> ucs2conv;
    try {
        std::u16string ucs2 = ucs2conv.from_bytes(utf8);
    } catch(const std::range_error& e) {
        std::u16string ucs2 = ucs2conv.from_bytes(utf8.substr(0, ucs2conv.converted()));
        std::cout << "UCS2 failed after producing " << std::dec << ucs2.size()<<" characters:\n";
        for(char16_t c : ucs2)
            std::cout << std::hex << std::showbase << c << '\n';
    }
}

: 

UTF16 conversion produced 4 code points:
0x7a
0x6c34
0xd834
0xdd0b
UCS2 failed after producing 2 characters:
0x7a
0x6c34

.

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> 		/
UCS2 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) 		codecvt_utf8<wchar_t> codecvt_utf16<wchar_t>
wide
(wchar_t) 		codecvt<wchar_t, char, mbstate_t>
mbsrtowcs / wcsrtombs
, UTF-8, UTF-16, UTF-32
( ) []
(C++11)( C++17)
 codecvt
() []
(C++11)( C++17)
 UTF-16 UCS-2/UCS-4
( ) []
(C++11)( C++17)
 UTF-8 UTF-16
( ) []
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