std::codecvt_utf8
STD：：编解码器[医]UTF8
| Defined in header | | |
|---|
| 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>; | | (since C++11) (deprecated in C++17) |
std::codecvt_utf8是std::codecvt方面，它封装Utf-8编码字节字符串与UC 2或UC 4字符串%28之间的转换，具体取决于Elem29%。这个编解码面可以用来读取和写入UTF-8文件，包括文本和二进制文件.
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 facet (public member function) |
|---|
| (destructor) | destroys a codecvt_utf8 facet (public member function) |
STD：：编解码器[医]UTF 8：[医]UTF8
| explicit codecvt_utf8( std::size_t refs = 0 | | |
|---|
构造一个新的std::codecvt_utf8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]UTF 8：~codecvt[医]UTF8
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
下面的示例演示了UCS 2/UTF-8和UTF-16/UTF-8转换之间的区别：字符串中的第三个字符不是有效的UC 2字符。
二次
#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';
}
}
二次
产出：
二次
UTF16 conversion produced 4 code points:
0x7a
0x6c34
0xd834
0xdd0b
UCS2 failed after producing 2 characters:
0x7a
0x6c34
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_utf16 (C++11)(deprecated in C++17) | converts between UTF-16 and UCS2/UCS4 (class template) |
| codecvt_utf8_utf16 (C++11)(deprecated in C++17) | converts between UTF-8 and UTF-16 (class template) |
在CreativeCommonsAttribution下授权-ShareAlike未移植许可v3.0。
http：//en.cppreference.com/w/cpp/locale/codecvt[医]UTF8
