NAME¶

std::codecvt::in,std::codecvt::do_in - std::codecvt::in,std::codecvt::do_in

Synopsis¶

Defined in header <locale>
public:

result in( StateT& state,
const ExternT* from,
const ExternT* from_end, (1)
const ExternT*& from_next,
InternT* to,
InternT* to_end,

InternT*& to_next ) const;
protected:

virtual result do_in( StateT& state,
const ExternT* from,
const ExternT* from_end, (2)
const ExternT*& from_next,
InternT* to,
InternT* to_end,

InternT*& to_next ) const;

1) Public member function, calls the member function do_in of the most derived
class.
2) If this codecvt facet defines a conversion, translates the external characters
from the source range [from, from_end) to internal characters, placing the results
in the subsequent locations starting at to. Converts no more than from_end - from
external characters and writes no more than to_end - to internal characters. Leaves
from_next and to_next pointing one beyond the last element successfully converted.

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
is returned.

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

* 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:

ok conversion completed
partial not enough space in the output buffer or unexpected end of source buffer
error encountered a character that could not be converted
noconv this facet is non-converting, no output written

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 either representing
the initial shift state or obtained by converting the preceding characters in the
sequence.

The effect on state is deliberately unspecified. In standard facets, it is used to
maintain shift state like when calling std::mbsrtowcs, and is therefore updated to
reflect the conversion state after the last processed external character, but a
user-defined facet is free to use it to maintain any other state, e.g. count the
number of special characters encountered.

Example¶

// Run this code

#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';
}

Output:¶

The string in wide encoding: zß水𝄋

Defect reports

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

DR Applied to Behavior as published Correct behavior
it was unclear whether the conversion is
LWG 76 C++98 required to only required if used
support producing one internal character at by basic_filebuf
a time

See also¶

underflow reads from the associated file
[virtual] (virtual protected member function of std::basic_filebuf<CharT,Traits>)

converts a byte string into a wide string
from_bytes (public member function of
std::wstring_convert<Codecvt,Elem,Wide_alloc,Byte_alloc>)
mbsrtowcs converts a narrow multibyte character string to wide string, given state
(function)
do_out converts a string from InternT to ExternT, such as when writing to file
[virtual] (virtual protected member function)