Defined in header <codecvt> | ||
|---|---|---|
template<
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>;
| (since C++11) (deprecated in C++17) |
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.
| 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 |
| (constructor) | constructs a new codecvt_utf8 facet (public member function) |
| (destructor) | 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 |
~codecvt_utf8(); |
Destroys the facet. Unlike the locale-managed facets, this facet's destructor is public.
| Member type | Definition |
|---|---|
intern_type | internT |
extern_type | externT |
state_type | stateT |
| Member name | Type |
|---|---|
id (static) | std::locale::id |
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) |
|
[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) |
| 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 |
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
| Character conversions | locale-defined multibyte (UTF-8, GB18030) | UTF-8 | UTF-16 |
|---|---|---|---|
| UTF-16 |
mbrtoc16 / c16rtomb(with C11's DR488) |
codecvt<char16_t, char, mbstate_t>codecvt_utf8_utf16<char16_t>codecvt_utf8_utf16<char32_t>codecvt_utf8_utf16<wchar_t> | N/A |
| UCS2 |
c16rtomb(without C11's DR488) |
codecvt_utf8<char16_t>
|
codecvt_utf16<char16_t>
|
| UTF-32 |
|
|
|
| system wide: UTF-32(non-Windows) UCS2(Windows) |
| No | No |
| converts between character encodings, including UTF-8, UTF-16, UTF-32 (class template) |
|
|
(C++11)(deprecated in C++17) | tags to alter behavior of the standard codecvt facets (enum) |
|
(C++11)(deprecated in C++17) | converts between UTF-16 and UCS2/UCS4 (class template) |
|
(C++11)(deprecated in C++17) | converts between UTF-8 and UTF-16 (class template) |
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