streams, stream_bufs, codecvt facets and \n to \r\n translation

Question

What part of the C++ IO streams does the \\r to \\r\\n conversion? Is it the stream_buf itself or is it part of the internal to external encoding conversion by codecvt facet?

UPDATE 1

You all say that it is done in streambuf/filebuf. Ok. But how does this arrangement deal with, eg, external encodings like UTF-16? Then it seems that the file has to be opened with ios::binary flag which disables the translation.

Answer 1

This conversion is not (usually) performed by stream, streambuf, or facet. It is the responsibility the C library code (eg fputc() ) that is called by streambuf's overflow() and underflow() .

If you need it for some reason (eg when implementing a dos2unix routine), there's a handy example in boost.iostreams.

EDIT: std::filebuf only supports multibyte encodings for text files, eg UTF-8 or GB18030 or whatever the locale uses. A UTF-16 file would have to be opened in binary mode, as a plain byte stream (which can be interpreted as UTF-16 with C++11's codecvt facilities), and yes the line endings would not get converted.

Answer 2

IFAIR在streambuf实现中完成， codecvt只处理区域设置表示细节。

Answer 3

它由std :: filebuf执行，如果它是在没有ios :: binary标志的情况下打开的话。