Defined in header <locale> | ||
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template< class InternT, class ExternT, class State > class codecvt; |
Class std::codecvt
encapsulates conversion of character strings, including wide and multibyte, from one encoding to another. All file I/O operations performed through std::basic_fstream<CharT>
use the std::codecvt<CharT, char, std::mbstate_t>
facet of the locale imbued in the stream.
Inheritance diagram.
Four standalone (locale-independent) specializations are provided by the standard library:
Defined in header <locale> | |
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std::codecvt<char, char, std::mbstate_t> | identity conversion |
std::codecvt<char16_t, char, std::mbstate_t> | conversion between UTF-16 and UTF-8 (since C++11) |
std::codecvt<char32_t, char, std::mbstate_t> | conversion between UTF-32 and UTF-8 (since C++11) |
std::codecvt<wchar_t, char, std::mbstate_t> | conversion between the system's native wide and multibyte encodings |
In addition, every locale object constructed in a C++ program implements its own (locale-specific) versions of these four specializations.
Member types
Member type | Definition |
---|---|
intern_type | InternT |
extern_type | ExternT |
state_type | State |
Member functions
constructs a new codecvt facet (public member function) | |
(destructor)
| destructs a codecvt facet (protected member function) |
invokes do_out (public member function) | |
invokes do_in (public member function) | |
invokes do_unshift (public member function) | |
invokes do_encoding (public member function) | |
invokes do_always_noconv (public member function) | |
invokes do_length (public member function) | |
invokes do_max_length (public member function) |
Member objects
Member name | Type |
---|---|
id (static) | std::locale::id |
Protected member functions
[virtual] | converts a string from internT to externT, such as when writing to file (virtual protected member function) |
[virtual] | converts a string from externT to internT, such as when reading from file (virtual protected member function) |
[virtual] | generates the termination character sequence of externT characters for incomplete conversion (virtual protected member function) |
[virtual] | returns the number of externT characters necessary to produce one internT character, if constant (virtual protected member function) |
[virtual] | tests if the facet encodes an identity conversion for all valid argument values (virtual protected member function) |
[virtual] | calculates the length of the externT string that would be consumed by conversion into given internT buffer (virtual protected member function) |
[virtual] | returns the maximum number of externT characters that could be converted into a single internT character (virtual protected member function) |
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 |
Example
The following examples reads a UTF-8 file using a locale which implements UTF-8 conversion in codecvt<wchar_t, char, mbstate_t> and converts a UTF-8 string to UTF-16 using one of the standard specializations of std::codecvt.
#include <iostream> #include <fstream> #include <string> #include <locale> #include <iomanip> #include <string> #include <codecvt> // utility wrapper to adapt locale-bound facets for wstring/wbuffer convert template<class Facet> struct deletable_facet : Facet { template<class ...Args> deletable_facet(Args&& ...args) : Facet(std::forward<Args>(args)...) {} ~deletable_facet() {} }; int main() { // UTF-8 narrow multibyte encoding std::string data = u8"z\u00df\u6c34\U0001f34c"; // or u8"zß水🍌" // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9f\x8d\x8c"; std::ofstream("text.txt") << data; // using system-supplied locale's codecvt facet std::wifstream fin("text.txt"); // reading from wifstream will use codecvt<wchar_t, char, mbstate_t> // this locale's codecvt converts UTF-8 to UCS4 (on systems such as Linux) fin.imbue(std::locale("en_US.UTF-8")); std::cout << "The UTF-8 file contains the following UCS4 code points: \n"; for (wchar_t c; fin >> c; ) std::cout << "U+" << std::hex << std::setw(4) << std::setfill('0') << c << '\n'; // using standard (locale-independent) codecvt facet std::wstring_convert< deletable_facet<std::codecvt<char16_t, char, std::mbstate_t>>, char16_t> conv16; std::u16string str16 = conv16.from_bytes(data); std::cout << "The UTF-8 file contains the following UTF-16 code points: \n"; for (char16_t c : str16) std::cout << "U+" << std::hex << std::setw(4) << std::setfill('0') << c << '\n'; }
Output:
The UTF-8 file contains the following UCS4 code points: U+007a U+00df U+6c34 U+1f34c The UTF-8 file contains the following UTF-16 code points: U+007a U+00df U+6c34 U+d83c U+df4c
See also
Character conversions | narrow multibyte (char) | UTF-8 (char) | UTF-16 (char16_t) |
---|---|---|---|
UTF-16 | mbrtoc16 (one way) | 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 (one way) | 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 |
defines character conversion errors (class template) | |
creates a codecvt facet for the named locale (class template) | |
(C++11) | converts between UTF-8 and UCS2/UCS4 (class template) |
(C++11) | converts between UTF-16 and UCS2/UCS4 (class template) |
(C++11) | converts between UTF-8 and UTF-16 (class template) |
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