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std::codecvt_utf8(3) C++ Standard Libary std::codecvt_utf8(3) NAME std::codecvt_utf8 - std::codecvt_utf8 Synopsis Defined in header <codecvt> template< class Elem, (since C++11) unsigned long Maxcode = 0x10ffff, (deprecated in C++17) std::codecvt_mode Mode = (std::codecvt_mode)0 > (removed in C++26) class codecvt_utf8 : public std::codecvt<Elem, char, std::mbstate_t>; std::codecvt_utf8 is a std::codecvt facet which encapsulates conver- sion between a UTF-8 encoded byte string and UCS-2 or UTF-32 character string (de- pending on the type of Elem). This std::codecvt facet can be used to read and write UTF-8 files, both text and binary. UCS-2 is the same encoding as UTF-16, except that it encodes scalar (since C++23) values in the range U+0000-U+FFFF (Basic Multilingual Plane) only. 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 Member functions constructor constructs a new codecvt_utf8 facet (public member function) destructor destroys a codecvt_utf8 facet (public member function) std::codecvt_utf8::codecvt_utf8 explicit codecvt_utf8( std::size_t refs = 0 ); Constructs a new std::codecvt_utf8 facet, passes the initial refer- ence counter refs to the base class. Parameters refs - the number of references that link to the facet std::codecvt_utf8::~codecvt_utf8 ~codecvt_utf8(); Destroys the facet. Unlike the locale-managed facets, this facet's destructor is public. 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 invokes do_out out (public member function of std::codecvt<InternT,Ex- ternT,StateT>) invokes do_in in (public member function of std::codecvt<InternT,Ex- ternT,StateT>) invokes do_unshift unshift (public member function of std::codecvt<InternT,Ex- ternT,StateT>) invokes do_encoding encoding (public member function of std::codecvt<InternT,Ex- ternT,StateT>) invokes do_always_noconv always_noconv (public member function of std::codecvt<InternT,Ex- ternT,StateT>) invokes do_length length (public member function of std::codecvt<InternT,Ex- ternT,StateT>) invokes do_max_length max_length (public member function of std::codecvt<InternT,Ex- ternT,StateT>) Protected member functions converts a string from InternT to ExternT, such as when writing to do_out file [virtual] (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) converts a string from ExternT to InternT, such as when reading do_in from file [virtual] (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) generates the termination character sequence of Ex- ternT characters do_unshift for incomplete conversion [virtual] (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) returns the number of ExternT characters necessary to produce one do_encoding InternT character, if constant [virtual] (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) tests if the facet encodes an identity conversion for all valid do_always_noconv argument values [virtual] (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) calculates the length of the ExternT string that would be consumed do_length by conversion into given InternT buffer [virtual] (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) returns the maximum number of ExternT characters that could be do_max_length converted into a single InternT character [virtual] (virtual protected member function of std::codecvt<InternT,ExternT,StateT>) 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 Notes Although the standard requires that this facet works with UCS-2 when the size of Elem is 16 bits, some implementations use UTF-16 instead. The term "UCS-2" was deprecated and removed from ISO 10646. Since C++23, UCS-2 does not refer to its original definition any- more. It becomes a synonym of UTF-16, but with a smaller encoding range. Example The following example demonstrates the difference between UCS-2/UTF-8 and UTF-16/UTF-8 conversions: the third character in the string is not a valid UCS-2 character. // Run this code #include <codecvt> #include <cstdint> #include <iostream> #include <locale> #include <string> int main() { // UTF-8 data. The character U+1d10b, musical sign segno, does not fit in UCS-2 std::string utf8 = "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 << "UTF-16 conversion produced " << utf16.size() << " code units:\n" << std::showbase << std::hex; for (char16_t c : utf16) std::cout << static_cast<std::uint16_t>(c) << ' '; // the UTF-8 / UCS-2 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 << "\nUCS-2 failed after producing " << std::dec << ucs2.size() << " characters:\n" << std::showbase << std::hex; for (char16_t c : ucs2) std::cout << static_cast<std::uint16_t>(c) << ' '; std::cout << '\n'; } } Output: UTF-16 conversion produced 4 code units: 0x7a 0x6c34 0xd834 0xdd0b UCS-2 failed after producing 2 characters: 0x7a 0x6c34 See also Character locale-defined multibyte UTF-8 UTF-16 conversions (UTF-8, GB18030) codecvt<char16_t,char,mb- state_t> UTF-16 mbrtoc16 / c16rtomb (with C11's codecvt_utf8_utf16<char16_t> N/A DR488) codecvt_utf8_utf16<char32_t> codecvt_utf8_utf16<wchar_t> 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_utf16<char32_t> codecvt_utf8<char32_t> system wchar_t: mbsrtowcs / wcsrtombs UTF-32 use_facet<codecvt codecvt_utf8<wchar_t> codecvt_utf16<wchar_t> (non-Windows) <wchar_t,char,mbstate_t>>(locale) UCS-2 (Windows) converts between character encodings, includ- ing UTF-8, UTF-16, codecvt UTF-32 (class template) codecvt_mode (C++11) tags to alter behavior of the standard codecvt facets (deprecated in C++17) (enum) (removed in C++26) codecvt_utf16 (C++11) converts between UTF-16 and UCS-2/UCS-4 (deprecated in C++17) (class template) (removed in C++26) codecvt_utf8_utf16 (C++11) converts between UTF-8 and UTF-16 (deprecated in C++17) (class template) (removed in C++26) http://cppreference.com 2024.06.10 std::codecvt_utf8(3)
NAME | Synopsis | Template Parameters | Member functions | Parameters | Member types | Member objects | Member functions | Protected member functions | Notes | Example | Output: | See also
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