From cppreference.com
template<classElem,unsignedlongMaxcode=0x10ffff,std::codecvt_modeMode=(std::codecvt_mode)0>classcodecvt_utf8:publicstd::codecvt<Elem,char,std::mbstate_t>;(since C++11)
(deprecated in C++17)
(removed in C++26)std::codecvt_utf8 is a
facet which encapsulates conversion between a UTF-8 encoded byte string and UCS-2 or UTF-32 character string (depending on the type of Elem). This
facet can be used to read and write UTF-8 files, both text and binary.
UCS-2 is an archaic encoding that is a subset of UTF-16, which encodes scalar values in the range U+0000-U+FFFF (Basic Multilingual Plane) only.
Template Parameters
Elem - either char16_t, char32_t, or wchar_tMaxcode - the largest value of Elem that this facet will read or write without error Mode - a constant of type
Member functions
constructs a new codecvt_utf8 facet
(public member function)destroys a codecvt_utf8 facet
(public member function)std::codecvt_utf8::codecvt_utf8
explicitcodecvt_utf8(std::size_trefs=0);Constructs a new std::codecvt_utf8 facet, passes the initial reference counter refs to the base class.
Parameters
refs - the number of references that link to the facet std::codecvt_utf8::~codecvt_utf8
~codecvt_utf8();Destroys the facet. Unlike the locale-managed facets, this facet's destructor is public.
Inherited from
Nested types
Type Definition intern_typeinternTextern_typeexternTstate_typestateTData members
Member functions
invokes do_out
(public member function of std::codecvt<InternT,ExternT,StateT>)
invokes do_in
(public member function of std::codecvt<InternT,ExternT,StateT>)
invokes do_unshift
(public member function of std::codecvt<InternT,ExternT,StateT>)
invokes do_encoding
(public member function of std::codecvt<InternT,ExternT,StateT>)
invokes do_always_noconv
(public member function of std::codecvt<InternT,ExternT,StateT>)
invokes do_length
(public member function of std::codecvt<InternT,ExternT,StateT>)
invokes do_max_length
(public member function of std::codecvt<InternT,ExternT,StateT>)
Protected member functions
[virtual]
converts a string from InternT to ExternT, such as when writing to file
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>)
[virtual]
converts a string from ExternT to InternT, such as when reading from file
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>)
[virtual]
generates the termination character sequence of ExternT characters for incomplete conversion
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>)
[virtual]
returns the number of ExternT characters necessary to produce one InternT character, if constant
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>)
[virtual]
tests if the facet encodes an identity conversion for all valid argument values
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>)
[virtual]
calculates the length of the ExternT string that would be consumed by conversion into given InternT buffer
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>)
[virtual]
returns the maximum number of ExternT characters that could be converted into a single InternT character
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>)
Inherited from
Nested type Definition enumresult{ok,partial,error,noconv};Unscoped enumeration type Enumeration constant Definition okconversion was completed with no error partialnot all source characters were converted errorencountered an invalid character noconvno conversion required, input and output types are the same Notes
Although the standard requires that this facet works with UCS-2 when the size of Elem is 16 bits, some implementations use UTF-16 instead. The term "UCS-2" was deprecated and removed from ISO 10646.
Example
The following example demonstrates the difference between UCS-2/UTF-8 and UTF-16/UTF-8 conversions: the third character in the string is not a valid UCS-2 character.
Run this code
#include<codecvt>#include<cstdint>#include<iostream>#include<locale>#include<string>intmain(){// UTF-8 data. The character U+1d10b, musical sign segno, does not fit in UCS-2std::stringutf8="z\u6c34\U0001d10b";// the UTF-8 / UTF-16 standard conversion facetstd::wstring_convert<std::codecvt_utf8_utf16<char16_t>,char16_t>utf16conv;std::u16stringutf16=utf16conv.from_bytes(utf8);std::cout<<"UTF-16 conversion produced "<<utf16.size()<<" code units:\n"<<std::showbase<<std::hex;for(char16_tc:utf16)std::cout<<static_cast<std::uint16_t>(c)<<' ';// the UTF-8 / UCS-2 standard conversion facetstd::wstring_convert<std::codecvt_utf8<char16_t>,char16_t>ucs2conv;try{std::u16stringucs2=ucs2conv.from_bytes(utf8);}catch(conststd::range_error&e){std::u16stringucs2=ucs2conv.from_bytes(utf8.substr(0,ucs2conv.converted()));std::cout<<"\nUCS-2 failed after producing "<<std::dec<<ucs2.size()<<" characters:\n"<<std::showbase<<std::hex;for(char16_tc:ucs2)std::cout<<static_cast<std::uint16_t>(c)<<' ';std::cout<<'\n';}}Output:
UTF-16 conversion produced 4 code units: 0x7a 0x6c34 0xd834 0xdd0b UCS-2 failed after producing 2 characters: 0x7a 0x6c34 Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 the constructor and destructor were not specified specifies them See also
Character
conversions locale-defined multibyte
(UTF-8, GB18030) UTF-8
UTF-16
UTF-16
/
(with C11's DR488)
<char16_t,char,mbstate_t>
<char16_t>
<char32_t>
<wchar_t>
N/AUCS-2
(without C11's DR488)
<char16_t>
<char16_t>UTF-32
/
<char32_t,char,mbstate_t>
<char32_t>
<char32_t>
system wchar_t: UTF-32 (non-Windows)
UCS-2 (Windows)
/
<
<wchar_t,char,mbstate_t>>(
)
<wchar_t>
<wchar_t>converts between character encodings, including UTF-8, UTF-16, UTF-32
(class template)
(C++11)(deprecated in C++17)(removed in C++26)
tags to alter behavior of the standard codecvt facets
(enum)
(C++11)(deprecated in C++17)(removed in C++26)
converts between UTF-16 and UCS-2/UCS-4
(class template)
(C++11)(deprecated in C++17)(removed in C++26)
converts between UTF-8 and UTF-16
(class template)