< cpp‎ | locale
Defined in header <codecvt>

    class Elem,
    unsigned long Maxcode = 0x10ffff,
    std::codecvt_mode Mode = (std::codecvt_mode)0

> 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 UCS4 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.


[edit] 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

[edit] Member functions

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


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.


refs - the number of references that link to the facet



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

invokes do_out
(public member function of std::codecvt)
invokes do_in
(public member function of std::codecvt)
invokes do_unshift
(public member function of std::codecvt)
invokes do_encoding
(public member function of std::codecvt)
invokes do_always_noconv
(public member function of std::codecvt)
invokes do_length
(public member function of std::codecvt)
invokes do_max_length
(public member function of std::codecvt)

Protected member functions

converts a string from internT to externT, such as when writing to file
(virtual protected member function of std::codecvt)
converts a string from externT to internT, such as when reading from file
(virtual protected member function of std::codecvt)
generates the termination character sequence of externT characters for incomplete conversion
(virtual protected member function of std::codecvt)
returns the number of externT characters necessary to produce one internT character, if constant
(virtual protected member function of std::codecvt)
tests if the facet encodes an identity conversion for all valid argument values
(virtual protected member function of std::codecvt)
calculates the length of the externT string that would be consumed by conversion into given internT buffer
(virtual protected member function of std::codecvt)
returns the maximum number of externT characters that could be converted into a single internT character
(virtual protected member function of std::codecvt)

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

[edit] 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.

#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 points:\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';


UTF16 conversion produced 4 code points:
UCS2 failed after producing 2 characters:

[edit] See also

narrow multibyte
UTF-16 mbrtoc16(one way) codecvt<char16_t, char, mbstate_t>
UCS2 c16rtomb(one way) codecvt_utf8<char16_t> codecvt_utf16<char16_t>
mbrtoc32 / c32rtomb codecvt<char32_t, char, mbstate_t>
No codecvt_utf8<wchar_t> codecvt_utf16<wchar_t>
codecvt<wchar_t, char, mbstate_t>
mbsrtowcs / wcsrtombs
No No
converts between character encodings, including UTF-8, UTF-16, UTF-32
(class template)
tags to alter behavior of the standard codecvt facets
converts between UTF-16 and UCS2/UCS4
(class template)
converts between UTF-8 and UTF-16
(class template)