NAME¶

std::codecvt_utf8 - std::codecvt_utf8

Synopsis¶

Defined in header <codecvt>
template<

class Elem,
unsigned long Maxcode = 0x10ffff, (since C++11)
std::codecvt_mode Mode = (std::codecvt_mode)0 (deprecated in C++17)

> class codecvt_utf8 : public std::codecvt<Elem, char,
std::mbstate_t>;

std::codecvt_utf8 is a std::codecvt facet which encapsulates conversion between a
UTF-8 encoded byte string and UCS2 or UTF-32 character string (depending on the type
of Elem). This codecvt facet can be used to read and write UTF-8 files, both text
and binary.

Template Parameters¶

Elem - either char16_t, char32_t, or wchar_t
Maxcode - the largest value of Elem that this facet will read or write without error
Mode - a constant of type std::codecvt_mode

Member functions¶

constructor constructs a new codecvt_utf8 facet
(public member function)
destructor destroys a codecvt_utf8 facet
(public member function)

std::codecvt_utf8::codecvt_utf8

explicit codecvt_utf8( std::size_t refs = 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 std::codecvt

Member types¶

Member type Definition
intern_type internT
extern_type externT
state_type stateT

Member objects¶

Member name Type
id (static) std::locale::id

Member functions¶

out invokes do_out
(public member function of std::codecvt<InternT,ExternT,State>)
in invokes do_in
(public member function of std::codecvt<InternT,ExternT,State>)
unshift invokes do_unshift
(public member function of std::codecvt<InternT,ExternT,State>)
encoding invokes do_encoding
(public member function of std::codecvt<InternT,ExternT,State>)
always_noconv invokes do_always_noconv
(public member function of std::codecvt<InternT,ExternT,State>)
length invokes do_length
(public member function of std::codecvt<InternT,ExternT,State>)
max_length invokes do_max_length
(public member function of std::codecvt<InternT,ExternT,State>)

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,State>)
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,State>)
generates the termination character sequence of externT characters
do_unshift for incomplete conversion
[virtual] (virtual protected member function of
std::codecvt<InternT,ExternT,State>)
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,State>)
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,State>)
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,State>)
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,State>)

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

Notes¶

Although the standard requires that this facet works with UCS2 when the size of Elem
is 16 bits, some implementations use UTF-16 instead. The term "UCS2" was deprecated
and removed from the Unicode standard.

Example¶

The following example demonstrates the difference between UCS2/UTF-8 and
UTF-16/UTF-8 conversions: the third character in the string is not a valid UCS2
character.

// Run this code

#include <iostream>
#include <string>
#include <locale>
#include <codecvt>

int main()
{
// UTF-8 data. The character U+1d10b, musical sign segno, does not fit in UCS2
std::string utf8 = u8"z\u6c34\U0001d10b";

// the UTF-8 / UTF-16 standard conversion facet
std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> utf16conv;
std::u16string utf16 = utf16conv.from_bytes(utf8);
std::cout << "UTF16 conversion produced " << utf16.size() << " code units:\n";
for (char16_t c : utf16)
std::cout << std::hex << std::showbase << c << '\n';

// the UTF-8 / UCS2 standard conversion facet
std::wstring_convert<std::codecvt_utf8<char16_t>, char16_t> ucs2conv;
try {
std::u16string ucs2 = ucs2conv.from_bytes(utf8);
} catch(const std::range_error& e) {
std::u16string ucs2 = ucs2conv.from_bytes(utf8.substr(0, ucs2conv.converted()));
std::cout << "UCS2 failed after producing " << std::dec << ucs2.size()<<" characters:\n";
for (char16_t c : ucs2)
std::cout << std::hex << std::showbase << c << '\n';
}
}

Output:¶

UTF16 conversion produced 4 code units:
0x7a
0x6c34
0xd834
0xdd0b
UCS2 failed after producing 2 characters:
0x7a
0x6c34

See also¶

Character locale-defined
conversions multibyte UTF-8 UTF-16
(UTF-8, GB18030)
mbrtoc16 / codecvt<char16_t, char, mbstate_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, mbstate_t> codecvt_utf16<char32_t>
UTF-32 mbrtoc32 / c32rtomb codecvt_utf8<char32_t> codecvt_utf16<wchar_t>(non-Windows)
codecvt_utf8<wchar_t>(non-Windows)
mbsrtowcs /
system wide: wcsrtombs UTF-32(non-Windows) use_facet<codecvt No No
UCS2(Windows) <wchar_t, char,
mbstate_t>>(locale)

converts between character encodings, including UTF-8,
codecvt UTF-16, UTF-32
(class template)
codecvt_mode tags to alter behavior of the standard codecvt facets
(C++11)(deprecated in C++17) (enum)
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)