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std::codecvt

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Revision as of 17:28, 29 June 2013 by SuperBoi45 (Talk | contribs)

 
C++
 
Localization library
 
std::codecvt
 
Defined in header <locale>
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.

cpp/locale/codecvt basecpp/locale/locale/facetstd-codecvt-inheritance.svg

Inheritance diagram

Four specializations are provided by the standard library and are implemented by all locale objects created in a C++ program:

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> locale-specific conversion between wide string and narrow, possibly multibyte, string

Contents

Member types

Member type Definition
intern_type InternT
extern_type ExternT
state_type State

Member functions

 constructs a new codecvt facet
(public member function)
destructs a codecvt facet
(protected member function)
invokes do_out
(public member function) [edit]
invokes do_in
(public member function) [edit]
invokes do_unshift
(public member function) [edit]
invokes do_encoding
(public member function) [edit]
invokes do_always_noconv
(public member function) [edit]
invokes do_length
(public member function) [edit]
invokes do_max_length
(public member function) [edit]

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) [edit]
[virtual]
 converts a string from ExternT to InternT, such as when reading from file
(virtual protected member function) [edit]
[virtual]
 generates the termination character sequence of ExternT characters for incomplete conversion
(virtual protected member function) [edit]
[virtual]
 returns the number of ExternT characters necessary to produce one InternT character, if constant
(virtual protected member function) [edit]
[virtual]
 tests if the facet encodes an identity conversion for all valid argument values
(virtual protected member function) [edit]
[virtual]
 calculates the length of the ExternT string that would be consumed by conversion into given InternT buffer
(virtual protected member function) [edit]
[virtual]
 returns the maximum number of ExternT characters that could be converted into a single InternT character
(virtual protected member function) [edit]

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>

Run this code
#include <iostream>
#include <fstream>
#include <string>
#include <locale>
#include <iomanip>
 
int main()
{
    // UTF-8 narrow multibyte encoding
    std::ofstream("text.txt") << u8"z\u00df\u6c34\U0001d10b"; // or u8"zß水𝄋"
                                           // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b";
    std::wifstream fin("text.txt");
    fin.imbue(std::locale("en_US.UTF-8")); // this locale's codecvt<wchar_t, char, mbstate_t>
                                           // converts UTF-8 to UCS4
    std::cout << "The UTF-8 file contains the following wide characters: \n";
    for(wchar_t c; fin >> c; )
        std::cout << "U+" << std::hex << std::setw(4) << std::setfill('0') << c << '\n';
}

Output: 

The UTF-8 file contains the following wide characters:
U+007a
U+00df
U+6c34
U+1d10b

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
UCS-2 c16rtomb (without C11's DR488) codecvt_utf8<char16_t> codecvt_utf16<char16_t>
UTF-32

mbrtoc32 / c32rtomb

codecvt<char32_t,char,mbstate_t>
codecvt_utf8<char32_t>

codecvt_utf16<char32_t>

system wchar_t:

UTF-32 (non-Windows)
UCS-2 (Windows)

mbsrtowcs / wcsrtombs
use_facet<codecvt
<wchar_t,char,mbstate_t>>(locale)

codecvt_utf8<wchar_t> codecvt_utf16<wchar_t>
defines character conversion errors
(class template)
creates a codecvt facet for the named locale
(class template)
(C++11)(deprecated in C++17)(removed in C++26)
 converts between UTF-8 and UCS-2/UCS-4
(class template) [edit]
(C++11)(deprecated in C++17)(removed in C++26)
 converts between UTF-16 and UCS-2/UCS-4
(class template) [edit]
(C++11)(deprecated in C++17)(removed in C++26)
 converts between UTF-8 and UTF-16
(class template) [edit]
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