c++ - Is there a codecvt decoding scenario where the destination buffer needs space for more than one internal character?

Question

When using std::codecvt's in method to decode an external byte sequence to an internal char sequence, is there a situation where the destination buffer of internal chars needs space for more than one internal char?

Here is some code for reference:

// const std::locale& loc;
// mbstate_t state;
// const char *extern_buf_ptr;
// const char *extern_buf_eptr;
const std::codecvt<wchar_t, char, mbstate_t> *pcodecvt = &std::use_facet<std::codecvt<wchar_t, char, mbstate_t> >(loc);

wchar_t intern_char;
wchar_t *tmp;
std::codecvt_base::result in_res = pcodecvt->in(state,
        extern_buf_ptr, extern_buf_eptr, extern_buf_ptr,
        &intern_char, &intern_char + 1, tmp);

This is a simplification of some template code that I have written to decode bytes read individually from a Winsock SOCKET, where the user desires "unbuffered" input. Basically, with each iteration of a loop, a byte is read into the external buffer. The loop terminates when in_res is not std::codecvt_base::partial.

What I am wondering is: Is there a scenario where a call to in() would require space in the destination buffer for more than one internal character? I.e., is there a scenario that would make the above-described loop an infinite loop?

Answer 1

§22.4.1.4.2/3その程度のメモがあります：

basic_filebufは、内部文字から外部文字へのマッピングが次のように行われることを前提とし1てNいますcodecvt。basic_filebuf

IO ストリームに適したロケールは、ユーザーの使用にも適しているように思えます。