std::codecvt::out, do_out
| Defined in header <locale>
|
||
| public: result out( StateT& state, |
(1) | |
| protected: virtual result do_out( StateT& state, |
(2) | |
do_out of the most derived class.codecvt facet defines a conversion, translates the internal characters from the source range [from, from_end) to external characters, placing the results in the subsequent locations starting at to. Converts no more than from_end - from internal characters and writes no more than to_end - to external 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.
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.
While codecvt supports N:M conversions (e.g. UTF-16 to UTF-8, where two internal characters may be necessary to decide what external characters to output), std::basic_filebuf can only use codecvt facets that define a 1:N conversion, that is it must be able to process one internal character at a time when writing to a file.
When performing N:M conversions, this function may return std::codecvt_base::partial after consuming all source characters (from_next == from_end). This means that another internal character is needed to complete the conversion (e.g. when converting UTF-16 to UTF-8, if the last character in the source buffer is a high surrogate).
The effect on state is deliberately unspecified. In standard facets, it is used to maintain shift state like when calling std::wcsrtombs, and is therefore updated to reflect the shift state after the last successfully converted 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
#include <iostream> #include <string> #include <locale> int main() { std::locale::global(std::locale("en_US.utf8")); auto& f = std::use_facet<std::codecvt<wchar_t, char, std::mbstate_t>>(std::locale()); std::wstring internal = L"z\u00df\u6c34\U0001f34c"; // L"zß水🍌" // note that the following can be done with wstring_convert std::mbstate_t mb{}; // initial shift state std::string external(internal.size() * f.max_length(), '\0'); const wchar_t* from_next; char* to_next; f.out(mb, &internal[0], &internal[internal.size()], from_next, &external[0], &external[external.size()], to_next); // error checking skipped for brevity external.resize(to_next - &external[0]); std::cout << "The string in narrow multibyte encoding: " << external << '\n'; }
Output:
The string in narrow multibyte encoding: zß水🍌
See also
| [virtual] |
writes characters to the associated file from the put area (virtual protected member function of std::basic_filebuf) |
| converts a wide string into a byte string (public member function of std::wstring_convert) | |
| converts a wide string to narrow multibyte character string, given state (function) | |
| [virtual] |
converts a string from externT to internT, such as when reading from file (virtual protected member function) |