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)