std::codecvt_utf8

From Cppreference

Defined in header `<codecvt>`

template< class Elem, unsigned long Maxcode = 0x10ffff, std::codecvt_mode Mode = (std::codecvt_mode)0 > class codecvt_utf8;

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] 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';
    }
}

Output:

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

[edit] See also

Character conversions	narrow multibyte (char)	UTF-8 (char)	UTF-16 (char16_t)
UTF-16	`mbrtoc16` / `c16rtombr`	`codecvt`<char16_t, char, mbstate_t> `codecvt_utf8_utf16`<char16_t> `codecvt_utf8_utf16`<char32_t> `codecvt_utf8_utf16`<wchar_t>	N/A
UCS2	No	`codecvt_utf8`<char16_t>	`codecvt_utf16`<char16_t>
UTF-32/UCS4 (char32_t)	`mbrtoc32` / `c32rtombr`	`codecvt`<char32_t, char, mbstate_t> `codecvt_utf8`<char32_t>	`codecvt_utf16`<char32_t>
UCS2/UCS4 (wchar_t)	No	`codecvt_utf8`<wchar_t>	`codecvt_utf16`<wchar_t>
wide (wchar_t)	`codecvt`<wchar_t, char, mbstate_t> `mbstowcs` / `wcstombs`	No	No

codecvt

converts between character encodings, including UTF-8, UTF-16, UTF-32
(class template)

codecvt_mode (C++11)

tags to alter behavior of the standard codecvt facets
(class)

codecvt_utf16 (C++11)

converts between UTF-16 and UCS2/UCS4
(class template)

codecvt_utf8_utf16 (C++11)

converts between UTF-8 and UTF-16
(class template)