std::codecvt_utf8
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 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
invokes do_out (public member function of std::codecvt<InternT,ExternT,State> ) |
|
invokes do_in (public member function of std::codecvt<InternT,ExternT,State> ) |
|
invokes do_unshift (public member function of std::codecvt<InternT,ExternT,State> ) |
|
invokes do_encoding (public member function of std::codecvt<InternT,ExternT,State> ) |
|
invokes do_always_noconv (public member function of std::codecvt<InternT,ExternT,State> ) |
|
invokes do_length (public member function of std::codecvt<InternT,ExternT,State> ) |
|
invokes do_max_length (public member function of std::codecvt<InternT,ExternT,State> ) |
Protected member functions
[virtual]
|
converts a string from internT to externT, such as when writing to file (virtual protected member function of std::codecvt<InternT,ExternT,State> ) |
[virtual]
|
converts a string from externT to internT, such as when reading from file (virtual protected member function of std::codecvt<InternT,ExternT,State> ) |
[virtual]
|
generates the termination character sequence of externT characters for incomplete conversion (virtual protected member function of std::codecvt<InternT,ExternT,State> ) |
[virtual]
|
returns the number of externT characters necessary to produce one internT character, if constant (virtual protected member function of std::codecvt<InternT,ExternT,State> ) |
[virtual]
|
tests if the facet encodes an identity conversion for all valid argument values (virtual protected member function of std::codecvt<InternT,ExternT,State> ) |
[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<InternT,ExternT,State> ) |
[virtual]
|
returns the maximum number of externT characters that could be converted into a single internT character (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.
#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 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) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/locale/codecvt_utf8