std::codecvt::encoding, do_encoding

C++

Language

Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

Localizations library

Locales and facets
locale
use_facet	has_facet
Character classification
isspace isblank (C++11) iscntrl isupper islower isalpha	isdigit ispunct isxdigit isalnum isprint isgraph
Conversions
toupper tolower	wstring_convert (C++11) wbuffer_convert (C++11)
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
Facet categories
ctype ctype<char> codecvt collate messages time_get time_put	num_get num_put numpunct money_get money_put moneypunct
Locale-specific facets
ctype_byname codecvt_byname messages_byname collate_byname	time_get_byname time_put_byname numpunct_byname moneypunct_byname
Code conversion facets
codecvt_utf8 (C++11) codecvt_utf16 (C++11)	codecvt_utf8_utf16 (C++11) codecvt_mode (C++11)
C locale
setlocale localeconv lconv	LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME

std::codecvt

Member functions

codecvt::codecvt

codecvt::~codecvt

codecvt::outcodecvt::do_out

codecvt::incodecvt::do_in

codecvt::unshiftcodecvt::do_unshift

codecvt::encodingcodecvt::do_encoding

codecvt::always_noconvcodecvt::do_always_noconv

codecvt::lengthcodecvt::do_length

codecvt::max_lengthcodecvt::do_max_length

Defined in header <locale>
public: int encoding() const;	(1)
protected: virtual int do_encoding() const;	(2)

1) public member function, calls the member function do_encoding of the most derived class.

2) if the encoding represented by this codecvt facet maps each internal character to the same, constant number of external characters, returns that number. If the encoding is variable-length (e.g. UTF-8 or UTF-16), returns 0. If the encoding is state-dependent, returns -1.

Return value

The exact number of externT characters that correspond to one internT character, if constant. 0 if the number varies, -1 if the encoding is state-dependent.

The non-converting specialization std::codecvt<char, char, std::mbstate_t> returns 1

Exceptions

(none)	(until C++11)
noexcept specification: noexcept	(since C++11)

Example

Run this code

#include <locale>
#include <iostream>

int main()
{
    std::cout << "en_US.utf8 is a variable-length encoding, encoding() returns "
              << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
                    std::locale("en_US.utf8")
              ).encoding() << '\n';

    std::cout << "zh_CN.gb18030 is also variable-length, encoding() == "
              << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
                    std::locale("zh_CN.gb18030")
              ).encoding() << '\n';

    std::cout << "ru_RU.koi8r is a single-byte encoding encoding() == "
              << std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(
                    std::locale("ru_RU.koi8r")
              ).encoding() << '\n';
}

Output:

en_US.utf8 is a variable-length encoding, encoding() returns 0
zh_CN.gb18030 is also variable-length, encoding() == 0
ru_RU.koi8r is a single-byte encoding encoding() == 1

See also

MB_CUR_MAX	maximum number of bytes in a multibyte character in the current C locale (macro variable)
do_max_length [virtual]	returns the maximum number of externT characters that could be converted into a single internT character (virtual protected member function)