std::codecvt_utf8_utf16

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>;		(since C++11) (deprecated in C++17)

std::codecvt_utf8_utf16是std::codecvt方面，它封装了UTF-8编码字节字符串和UTF-16编码字符串之间的转换。如果Elem是一种32位类型，一个UTF-16码单元将存储在每个32位字符的输出序列中.

这是一个N：m转换面，不能与std::basic_filebuf%28，它只允许内部编码和外部编码之间的1：n转换，例如UTF-32/UTF-8。此方面可用于std::wstring_convert...

模板参数

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

成员函数

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

STD：：编解码器[医]UTF8[医]utf 16：：codecvt[医]UTF8[医]utf 16

explicit codecvt_utf8_utf16( std::size_t refs = 0 );

构造一个新的std::codecvt_utf8_utf16方面，传递初始参考计数器。refs给基类。

参数

refs	-	the number of references that link to the facet

STD：：编解码器[医]UTF8[医]utf 16：：~codecvt[医]UTF8[医]utf 16

~codecvt_utf8_utf16();

摧毁了这个面。与地区管理的方面不同，这个方面%27 s析构函数是公共的。

继承自STD：：编解码器

成员类型

Member type	Definition
intern_type	internT
extern_type	externT
state_type	stateT

成员对象

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

成员函数

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)

受保护成员函数

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)

继承自STD：：编解码器[医]底座

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

例

二次

#include <iostream>
#include <string>
#include <codecvt>
#include <cassert>
#include <locale>
 
int main()
{
    std::string u8 = u8"z\u00df\u6c34\U0001f34c";
    std::u16string u16 = u"z\u00df\u6c34\U0001f34c";
 
    // UTF-8 to UTF-16/char16_t
    std::u16string u16_conv = std::wstring_convert<
        std::codecvt_utf8_utf16<char16_t>, char16_t>{}.from_bytes(u8);
    assert(u16 == u16_conv);
    std::cout << "UTF-8 to UTF-16 conversion produced "
              << u16_conv.size() << " code units:\n";
    for (char16_t c : u16_conv)
        std::cout << std::hex << std::showbase << c << ' ';
 
    // UTF-16/char16_t to UTF-8
    std::string u8_conv = std::wstring_convert<
        std::codecvt_utf8_utf16<char16_t>, char16_t>{}.to_bytes(u16);
    assert(u8 == u8_conv);
    std::cout << "\nUTF-16 to UTF-8 conversion produced "
              << std::dec << u8_conv.size() << " bytes:\n" << std::hex;
    for (char c : u8_conv)
        std::cout << +(unsigned char)c << ' ';
}

二次

产出：

二次

UTF-8 to UTF-16 conversion produced 5 code units:
0x7a 0xdf 0x6c34 0xd83c 0xdf4c 
UTF-16 to UTF-8 conversion produced 10 bytes:
0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c

二次

另见

Characterconversions	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
UCS2	c16rtomb(without C11's DR488)	codecvt_utf8<char16_t> codecvt_utf8<wchar_t>(Windows).	codecvt_utf16<char16_t> codecvt_utf16<wchar_t>(Windows).
UTF-32	mbrtoc32 / c32rtomb.	codecvt<char32_t, char, mbstate_t> codecvt_utf8<char32_t> codecvt_utf8<wchar_t>(non-Windows).	codecvt_utf16<char32_t> codecvt_utf16<wchar_t>(non-Windows).
system wide:UTF-32(non-Windows)UCS2(Windows)	mbsrtowcs / wcsrtombs use_facet<codecvt <wchar_t, char, mbstate_t>>(locale).	No	No

codecvt	converts between character encodings, including UTF-8, UTF-16, UTF-32 (class template)
codecvt_mode (C++11)(deprecated in C++17)	tags to alter behavior of the standard codecvt facets (enum)
codecvt_utf8 (C++11)(deprecated in C++17)	converts between UTF-8 and UCS2/UCS4 (class template)
codecvt_utf16 (C++11)(deprecated in C++17)	converts between UTF-16 and UCS2/UCS4 (class template)

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最后更新于：2017-12-18