std::codecvt_utf8 is a std::codecvt facet which encapsulates conversion between a UTF-8 encoded byte string and UCS-2 or UTF-32 character string (depending on the type of Elem). This std::codecvt facet can be used to read and write UTF-8 files, both text and binary.
UCS-2 is an archaic encoding that is a subset of UTF-16, which encodes scalar values in the range U+0000-U+FFFF (Basic Multilingual Plane) only.
[edit] Template Parameters Elem - either char16_t, char32_t, or wchar_t Maxcode - the largest value ofElem that this facet will read or write without error Mode - a constant of type std::codecvt_mode [edit] Member functions constructs a new codecvt_utf8 facet
codecvt_utf8 facet
Constructs a new std::codecvt_utf8 facet, passes the initial reference counter refs to the base class.
Destroys the facet. Unlike the locale-managed facets, this facet's destructor is public.
Inherited from std::codecvt Nested types Type Definitionintern_type internT extern_type externT state_type stateT [edit] Data members Member functions invokes do_out
std::codecvt<InternT,ExternT,StateT>) [edit] invokes do_in
std::codecvt<InternT,ExternT,StateT>) [edit] invokes do_unshift
std::codecvt<InternT,ExternT,StateT>) [edit] invokes do_encoding
std::codecvt<InternT,ExternT,StateT>) [edit] invokes do_always_noconv
std::codecvt<InternT,ExternT,StateT>) [edit] invokes do_length
std::codecvt<InternT,ExternT,StateT>) [edit] invokes do_max_length
std::codecvt<InternT,ExternT,StateT>) [edit] Protected member functions converts a string from InternT to ExternT, such as when writing to file
std::codecvt<InternT,ExternT,StateT>) [edit] converts a string from ExternT to InternT, such as when reading from file
std::codecvt<InternT,ExternT,StateT>) [edit] generates the termination character sequence of ExternT characters for incomplete conversion
std::codecvt<InternT,ExternT,StateT>) [edit] returns the number of ExternT characters necessary to produce one InternT character, if constant
std::codecvt<InternT,ExternT,StateT>) [edit] tests if the facet encodes an identity conversion for all valid argument values
std::codecvt<InternT,ExternT,StateT>) [edit] calculates the length of the ExternT string that would be consumed by conversion into given InternT buffer
std::codecvt<InternT,ExternT,StateT>) [edit] returns the maximum number of ExternT characters that could be converted into a single InternT character
std::codecvt<InternT,ExternT,StateT>) [edit] Inherited from std::codecvt_base Nested 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] Notes
Although the standard requires that this facet works with UCS-2 when the size of Elem is 16 bits, some implementations use UTF-16 instead. The term "UCS-2" was deprecated and removed from ISO 10646.
The following example demonstrates the difference between UCS-2/UTF-8 and UTF-16/UTF-8 conversions: the third character in the string is not a valid UCS-2 character.
Output:
UTF-16 conversion produced 4 code units: 0x7a 0x6c34 0xd834 0xdd0b UCS-2 failed after producing 2 characters: 0x7a 0x6c34[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 2229 C++98 the constructor and destructor were not specified specifies them [edit] See also converts between character encodings, including UTF-8, UTF-16, UTF-32(C++11)(deprecated in C++17)(removed in C++26)
tags to alter behavior of the standard codecvt facets(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)
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