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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 State > 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 The following standalone (locale-independent) specializations are provided by the standard library: Defined in header <locale> std::codecvt<char, char, std::mbstate_t> identity conversion std::codecvt<char16_t, char, conversion between UTF-16 and UTF-8 (since std::mbstate_t> C++11)(deprecated in C++20) std::codecvt<char16_t, char8_t, conversion between UTF-16 and UTF-8 (since std::mbstate_t> C++20) std::codecvt<char32_t, char, conversion between UTF-32 and UTF-8 (since std::mbstate_t> C++11)(deprecated in C++20) std::codecvt<char32_t, char8_t, conversion between UTF-32 and UTF-8 (since std::mbstate_t> C++20) std::codecvt<wchar_t, char, conversion between the sys- tem's native wide std::mbstate_t> and the single-byte narrow character sets In addition, every locale object constructed in a C++ program imple- ments its own (locale-specific) versions of above specializations. Member types Member type Definition intern_type InternT extern_type ExternT state_type State Member functions constructor constructs a new codecvt facet (public member function) destructor destructs a codecvt facet (protected 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 Member name Type id [static] std::locale::id Protected member functions 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, mbstate_t> and converts a UTF-8 string to UTF-16 using one of the standard specializations of std::codecvt. // Run this code #include <iostream> #include <fstream> #include <string> #include <locale> #include <iomanip> #include <codecvt> #include <cstdint> // 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, 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: "; for (wchar_t c; fin >> c; ) std::cout << "U+" << std::hex << std::setw(4) << std::set- fill('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 << "\nThe UTF-8 file contains the following UTF-16 code units: "; for (char16_t c : str16) std::cout << "U+" << std::hex << std::setw(4) << std::set- fill('0') << static_cast<uint16_t>(c) << ' '; } 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 conversions multibyte UTF-8 UTF-16 (UTF-8, GB18030) mbrtoc16 / codecvt<char16_t, char, mb- state_t> UTF-16 c16rtomb(with C11's codecvt_utf8_utf16<char16_t> N/A DR488) codecvt_utf8_utf16<char32_t> codecvt_utf8_utf16<wchar_t> c16rtomb(without codecvt_utf8<char16_t> codecvt_utf16<char16_t> UCS2 C11's DR488) codecvt_utf8<wchar_t>(Windows) codecvt_utf16<wchar_t>(Windows) codecvt<char32_t, char, mb- state_t> codecvt_utf16<char32_t> UTF-32 mbrtoc32 / c32rtomb codecvt_utf8<char32_t> codecvt_utf16<wchar_t>(non-Windows) codecvt_utf8<wchar_t>(non-Win- dows) mbsrtowcs / system wide: wcsrtombs UTF-32(non-Windows) use_facet<codecvt No No UCS2(Windows) <wchar_t, char, mbstate_t>>(locale) codecvt_base defines character conversion errors (class template) codecvt_byname creates a codecvt facet for the named locale (class template) codecvt_utf8 converts between UTF-8 and UCS2/UCS4 (C++11)(deprecated in C++17) (class template) codecvt_utf16 converts between UTF-16 and UCS2/UCS4 (C++11)(deprecated in C++17) (class template) codecvt_utf8_utf16 converts between UTF-8 and UTF-16 (C++11)(deprecated in C++17) (class template) http://cppreference.com 2022.07.31 std::codecvt(3)
NAME | Synopsis | Member types | Member functions | Member objects | Protected member functions | Example | Output: | See also
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