std::codecvt<InternT,ExternT,StateT>::in, std::codecvt<InternT,ExternT,StateT>::

If this codecvt facet does not define a conversion, no characters are converted. to_next is set to be equal to to, state is unchanged, and std::codecvt_base::noconv

do_in(state, from, from_end, from_next, to, to + 1, to_next) must return ok

• this codecvt facet is used by basic_filebuf, and
• do_in(state, from, from_end, from_next, to, to_end, to_next) would return ok where to != to_end

Return value

A value of type std::codecvt_base::result, indicating the success status as follows:

The non-converting specialization std::codecvt < char, char, std::mbstate_t > always returns std::codecvt_base::noconv

Notes

Requires that from <= from_end && to <= to_end and that state

The effect on state is deliberately unspecified. In standard facets, it is used to maintain shift state like when calling std::mbsrtowcs

Example

#include <iostream>
#include <locale>
#include <string>
 
int main()
{
    std::locale::global(std::locale("en_US.utf8"));
    auto const& f = std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>
        (std::locale());
    std::string external = "z\u00df\u6c34\U0001d10b"; // or u8"zß水𝄋"
                     // or "\x7a\xc3\x9f\xe6\xb0\xb4\xf0\x9d\x84\x8b"
 
    // note that the following can be done with wstring_convert
    std::mbstate_t mb = std::mbstate_t(); // initial shift state
    std::wstring internal(external.size(), '\0'); 
    const char* from_next;
    wchar_t* to_next;
    f.in(mb, &external[0], &external[external.size()], from_next,
             &internal[0], &internal[internal.size()], to_next);
    // error checking skipped for brevity
    internal.resize(to_next - &internal[0]);
 
    std::wcout << L"The string in wide encoding: " << internal << '\n';
}

The string in wide encoding: zß水𝄋

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also