std::codecvt
| Defined in header  <locale> | ||
| template<      class InternT,  | ||
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.
Four standalone (locale-independent) specializations are provided by the standard library:
| Defined in header  <locale> | |
| 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.
| Contents | 
[edit] Member types
| Member type | Definition | 
| intern_type | InternT | 
| extern_type | ExternT | 
| state_type | State | 
[edit] Member functions
| constructs a new codecvt facet (public member function) | |
| 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) | 
[edit] Member objects
| Member name | Type | 
| id(static) | std::locale::id | 
[edit] 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 | 
[edit] 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 willl 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
[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 | 
| 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) | 



