std::wstring_convert<Codecvt,Elem,Wide_alloc,Byte_alloc>:: wstring_convert

From cppreference.com
C++
Localization library
std::wstring_convert
wstring_convert ( ) : wstring_convert ( new Codecvt ) { }
(1)
explicit wstring_convert ( Codecvt * pcvt ) ;
(2)
wstring_convert ( Codecvt * pcvt, state_type state ) ;
(3)
explicit wstring_convert ( const byte_string & byte_err,
const wide_string & wide_err = wide_string ( ) ) ;
(4)
wstring_convert ( const std:: wstring_convert & ) = delete ;
(5) (since C++14)
Overload Data members
byte_err_string wide_err_string cvtptr cvtstate cvtcount
(1) default-initialized new Codecvt default-initialized uninitialized
(2) pcvt
(3) state
(4) byte_err wide_err new Codecvt state_type ( )
2,3) If pcvt is a null pointer, the behavior is undefined.
5) The copy constructor is deleted, wstring_convert is not CopyConstructible .

Parameters

pcvt - pointer to the conversion facet
state - initial value of the conversion shift state
byte_err - narrow string to display on errors
wide_err - wide string to display on errors

Example

Run this code 
#include <codecvt>
#include <locale>
#include <utility>
 
// utility wrapper to adapt locale-bound facets for wstring/wbuffer convert
template<class Facet>
struct deletable_facet : Facet
{
    using Facet::Facet; // inherit constructors
    ~deletable_facet() {}
};
 
int main()
{
    // UTF-16le / UCS4 conversion
    std::wstring_convert
        <std::codecvt_utf16<char32_t, 0x10ffff, std::little_endian>> u16to32;
 
    // UTF-8 / wide string conversion with custom messages
    std::wstring_convert<std::codecvt_utf8<wchar_t>> u8towide("Error!", L"Error!");
 
    // GB18030 / wide string conversion facet
    using F = deletable_facet<std::codecvt_byname<wchar_t, char, std::mbstate_t>>;
    std::wstring_convert<F> gbtowide(new F("zh_CN.gb18030"));
}

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 2175 C++11 pcvt could be a null pointer the behavior is undefined in this case
LWG 2176 C++11 constructors accepting single argument were implicit made explicit
P0935R0 C++11 the default constructor was explicit made implicit
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