class InternT,
class ExternT,
class StateT
Class template 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
[edit] SpecializationsThe standard library is guaranteed to provide the following specializations (they are required to be implemented by any locale object):
std::codecvt<char, char, std::mbstate_t> identity conversion std::codecvt<char16_t, char, std::mbstate_t>intern_type InternT extern_type ExternT state_type StateT [edit] Data members [edit] Member functions [edit] Protected member functions destructs a codecvt facet
InternT to ExternT, such as when writing to file
ExternT to InternT, such as when reading from file
ExternT characters for incomplete conversion
ExternT characters necessary to produce one InternT character, if constant
ExternT string that would be consumed by conversion into given InternT buffer
ExternT characters that could be converted into a single InternT character
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, std::mbstate_t> and converts a UTF-8 string to UTF-16 using one of the standard specializations of std::codecvt.
#include <codecvt>
#include <cstdint>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <locale>
#include <string>
// 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 = reinterpret_cast<const char*>(+u8"z\u00df\u6c34\U0001f34c");
// or reinterpret_cast<const char*>(+u8"zÃæ°´ð")
// 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, std::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 units:\n" << std::hex;
for (wchar_t c; fin >> c;)
std::cout << "U+" << std::setw(4) << std::setfill('0')
<< static_cast<uint32_t>(c) << ' ';
// 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 << "\n\nThe UTF-8 file contains the following UTF-16 code units:\n"
<< std::hex;
for (char16_t c : str16)
std::cout << "U+" << std::setw(4) << std::setfill('0')
<< static_cast<uint16_t>(c) << ' ';
std::cout << '\n';
}
Output:
The UTF-8 file contains the following UCS4 code units: U+007a U+00df U+6c34 U+1f34c The UTF-8 file contains the following UTF-16 code units: U+007a U+00df U+6c34 U+d83c U+df4c[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior LWG 3767 C++20 std::codecvt<char16_t, char8_t, std::mbstate_t> and(C++11)(deprecated in C++17)(removed in C++26)
converts between UTF-8 and UCS-2/UCS-4(C++11)(deprecated in C++17)(removed in C++26)
converts between UTF-16 and UCS-2/UCS-4(C++11)(deprecated in C++17)(removed in C++26)
converts between UTF-8 and UTF-16RetroSearch is an open source project built by @garambo | Open a GitHub Issue
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