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std::codecvt(3) C++ Standard Libary std::codecvt(3) NAME std::codecvt - std::codecvt Synopsis Defined in header <locale> template< class InternT, class ExternT, class StateT > class codecvt; Class template std::codecvt encapsulates conversion of character strings, including wide and multibyte, from one encoding to another. All file I/O oper- ations performed through std::basic_fstream<CharT> use the std::codecvt<CharT, char, std::mbstate_t> facet of the locale imbued in the stream. std-codecvt-inheritance.svg Inheritance diagram Specializations The standard library is guaranteed to provide the following special- izations (they are required to be implemented by any locale object): Defined in header <locale> std::codecvt<char, char, std::mbstate_t> identity conversion std::codecvt<char16_t, char, std::mbstate_t> conversion between UTF-16 and UTF-8 (since C++11)(deprecated in C++20) std::codecvt<char16_t, char8_t, std::mbstate_t> conversion between UTF-16 and UTF-8 (since C++20) std::codecvt<char32_t, char, std::mbstate_t> conversion between UTF-32 and UTF-8 (since C++11)(deprecated in C++20) std::codecvt<char32_t, char8_t, std::mbstate_t> conversion between UTF-32 and UTF-8 (since C++20) std::codecvt<wchar_t, char, conversion between the system's native std::mbstate_t> wide and the single-byte narrow character sets Member types Member name Definition intern_type InternT extern_type ExternT state_type StateT Member functions constructor constructs a new codecvt facet (public member function) out invokes do_out (public member function) in invokes do_in (public member function) unshift invokes do_unshift (public member function) encoding invokes do_encoding (public member function) always_noconv invokes do_always_noconv (public member function) length invokes do_length (public member function) max_length invokes do_max_length (public member function) Member objects static std::locale::id id id of the locale (public member object) Protected member functions destructor destructs a codecvt facet (protected member function) do_out converts a string from InternT to ExternT, such as when writing to [virtual] file (virtual protected member function) do_in converts a string from ExternT to InternT, such as when reading [virtual] from file (virtual protected member function) do_unshift generates the termination character sequence of Ex- ternT characters [virtual] for incomplete conversion (virtual protected member function) do_encoding returns the number of ExternT characters necessary to produce one [virtual] InternT character, if constant (virtual protected member function) do_always_noconv tests if the facet encodes an identity conversion for all valid [virtual] argument values (virtual protected member function) do_length calculates the length of the ExternT string that would be consumed [virtual] by conversion into given InternT buffer (virtual protected member function) do_max_length returns the maximum number of ExternT characters that could be [virtual] converted into a single InternT character (virtual protected member function) 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 examples reads a UTF-8 file using a locale which im- plements UTF-8 conversion in codecvt<wchar_t, char, std::mbstate_t> and converts a UTF-8 string to UTF-16 using one of the standard specializations of std::codecvt. // Run this code #include <codecvt> #include <cstdint> #include <fstream> #include <iomanip> #include <iostream> #include <locale> #include <string> // utility wrapper to adapt locale-bound facets for wstring/wbuffer convert template<class Facet> struct deletable_facet : Facet { template<class... Args> deletable_facet(Args&&... args) : Facet(std::for- ward<Args>(args)...) {} ~deletable_facet() {} }; int main() { // UTF-8 narrow multibyte encoding std::string data = reinterpret_cast<const char*>(+u8"z\u00df\u6c34\U0001f34c"); // or reinterpret_cast<const char*>(+u8"z") // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9f\x8d\x8c" std::ofstream("text.txt") << data; // using system-supplied locale's codecvt facet std::wifstream fin("text.txt"); // reading from wifstream will use codecvt<wchar_t, char, std::mb- state_t> // this locale's codecvt converts UTF-8 to UCS4 (on systems such as Linux) fin.imbue(std::locale("en_US.UTF-8")); std::cout << "The UTF-8 file contains the following UCS4 code units:\n" << std::hex; for (wchar_t c; fin >> c;) std::cout << "U+" << std::setw(4) << std::setfill('0') << static_cast<uint32_t>(c) << ' '; // using standard (locale-independent) codecvt facet std::wstring_convert< deletable_facet<std::codecvt<char16_t, char, std::mbstate_t>>, char16_t> conv16; std::u16string str16 = conv16.from_bytes(data); std::cout << "\n\nThe UTF-8 file contains the following UTF-16 code units:\n" << std::hex; for (char16_t c : str16) std::cout << "U+" << std::setw(4) << std::setfill('0') << static_cast<uint16_t>(c) << ' '; std::cout << '\n'; } Output: The UTF-8 file contains the following UCS4 code units: U+007a U+00df U+6c34 U+1f34c The UTF-8 file contains the following UTF-16 code units: U+007a U+00df U+6c34 U+d83c U+df4c 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) codecvt_base defines character conversion errors (class) represents the system-supplied std::codecvt for the named codecvt_byname locale (class template) codecvt_utf8 (C++11) converts between UTF-8 and UCS-2/UCS-4 (deprecated in C++17) (class template) (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(3)
NAME | Synopsis | Specializations | Member types | Member functions | Member objects | Protected member functions | Example | Output: | See also
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