std::codecvt_byname(3)

NAME
std::codecvt_byname - std::codecvt_byname

Synopsis
   Defined in header <locale>
   template< class InternT, class ExternT, class State >
   class codecvt_byname : public std::codecvt<InternT, ExternT, State>;
   std::codecvt_byname is a std::codecvt facet which encapsulates multibyte/wide
   character conversion rules of a locale specified at its construction.

Specializations
   The standard library is guaranteed to provide the following specializations:
   Defined in header <locale>
   std::codecvt_byname<char, char, identity conversion
   std::mbstate_t>
   std::codecvt_byname<char16_t, char, conversion between UTF-16 and UTF-8 (since
   std::mbstate_t> C++11)(deprecated in C++20)
   std::codecvt_byname<char16_t, char8_t, conversion between UTF-16 and UTF-8 (since
   std::mbstate_t> C++20)
   std::codecvt_byname<char32_t, char, conversion between UTF-32 and UTF-8 (since
   std::mbstate_t> C++11)(deprecated in C++20)
   std::codecvt_byname<char32_t, char8_t, conversion between UTF-32 and UTF-8 (since
   std::mbstate_t> C++20)
   std::codecvt_byname<wchar_t, char, locale-specific conversion between wide
   std::mbstate_t> string and narrow character sets

Member functions
   constructor constructs a new codecvt_byname facet
                 (public member function)
   destructor destroys a codecvt_byname facet
                 (protected member function) std::codecvt_byname::codecvt_byname
   explicit codecvt_byname( const char* name, std::size_t refs = 0 );
   explicit codecvt_byname( const std::string& name, std::size_t refs = (since C++11)
   0 );
   Constructs a new std::codecvt_byname facet for a locale with name.
   refs is used for resource management: if refs == 0, the implementation destroys the
   facet, when the last std::locale object holding it is destroyed. Otherwise, the
   object is not destroyed.

Parameters
   name - the name of the locale
   refs - the number of references that link to the facet std::codecvt_byname::~codecvt_byname
   protected:
   ~codecvt_byname();
   Destroys the facet. 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,ExternT,StateT>)
                 invokes do_in
   in (public member function of std::codecvt<InternT,ExternT,StateT>)
                 invokes do_unshift
   unshift (public member function of std::codecvt<InternT,ExternT,StateT>)
                 invokes do_encoding
   encoding (public member function of std::codecvt<InternT,ExternT,StateT>)
                 invokes do_always_noconv
   always_noconv (public member function of std::codecvt<InternT,ExternT,StateT>)
                 invokes do_length
   length (public member function of std::codecvt<InternT,ExternT,StateT>)
                 invokes do_max_length
   max_length (public member function of std::codecvt<InternT,ExternT,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 ExternT 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

Example
   This example demonstrates reading a GB18030-encoded file using the codecvt facet
   from a GB18030-aware locale. // Run this code
 #include <fstream>
 #include <iostream>
 #include <locale>
 #include <string>
 int main()
 {
     // GB18030 narrow multibyte encoding
     std::ofstream("text.txt") << "\x7a" // letter 'z', U+007a
                        "\x81\x30\x89\x38" // letter 'ß', U+00df
                        "\xcb\xae" // CJK ideogram '水' (water), U+6c34
                        "\x94\x32\xbc\x35"; // musical sign '𝄋' (segno), U+1d10b
     std::wifstream fin("text.txt");
     fin.imbue(std::locale(fin.getloc(),
               new std::codecvt_byname<wchar_t, char, std::mbstate_t>("zh_CN.gb18030")));
     for (wchar_t c; fin.get(c);)
         std::cout << std::hex << std::showbase << static_cast<unsigned>(c) << '\n';
 }

Possible output:
 0x7a
 0xdf
 0x6c34
 0x1d10b
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
     DR Applied to Behavior as published Correct behavior
                     the standard library did not need to two specializations are
   LWG 21 C++98 provide required
                     any std::codecvt_byname specializations

See also
   codecvt converts between character encodings, including UTF-8, UTF-16, UTF-32
           (class template)