std::codecvt_utf8
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | Defined in header  <codecvt> | ||
| template<      class Elem, | ||
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. 
| Contents | 
[edit] Template Parameters
| Elem | - | either char16_t, char32_t, or wchar_t | 
| Maxcode | - | the largest value of Elemthat this facet will read or write without error | 
| Mode | - | a constant of type std::codecvt_mode | 
[edit] Member functions
|  (constructor) | constructs a new codecvt_utf8facet(public member function) | 
|  (destructor) | destroys a codecvt_utf8facet(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
| 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
| [virtual] | converts a string from internT to externT, such as when writing to file (virtual protected member function of std::codecvt) | 
| [virtual] | converts a string from externT to internT, such as when reading from file (virtual protected member function of std::codecvt) | 
| [virtual] | generates the termination character sequence of externT characters for incomplete conversion (virtual protected member function of std::codecvt) | 
| [virtual] | returns the number of externT characters necessary to produce one internT character, if constant (virtual protected member function of std::codecvt) | 
| [virtual] | tests if the facet encodes an identity conversion for all valid argument values (virtual protected member function of std::codecvt) | 
| [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) | 
| [virtual] | 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.
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 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 / c16rtomb | 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 / c32rtomb | 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> mbsrtowcs / wcsrtombs | No | No | 
| converts between character encodings, including UTF-8, UTF-16, UTF-32 (class template) | |
| (C++11) | tags to alter behavior of the standard codecvt facets (enum) | 
| (C++11) | converts between UTF-16 and UCS2/UCS4 (class template) | 
| (C++11) | converts between UTF-8 and UTF-16 (class template) | 


