From Jason Turner

[depr.conversions.buffer]

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- ### Class template `wbuffer_convert` <a id="depr.conversions.buffer">[[depr.conversions.buffer]]</a>
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-
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- Class template `wbuffer_convert` looks like a wide stream buffer, but
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- performs all its I/O through an underlying byte stream buffer that you
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- specify when you construct it. Like class template `wstring_convert`, it
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- lets you specify a code conversion facet to perform the conversions,
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- without affecting any streams or locales.
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-
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- ``` cpp
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- namespace std {
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- template<class Codecvt, class Elem = wchar_t, class Tr = char_traits<Elem>>
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- class wbuffer_convert : public basic_streambuf<Elem, Tr> {
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- public:
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- using state_type = typename Codecvt::state_type;
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-
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- wbuffer_convert() : wbuffer_convert(nullptr) {}
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- explicit wbuffer_convert(streambuf* bytebuf,
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- Codecvt* pcvt = new Codecvt,
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- state_type state = state_type());
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-
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- ~wbuffer_convert();
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-
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- wbuffer_convert(const wbuffer_convert&) = delete;
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- wbuffer_convert& operator=(const wbuffer_convert&) = delete;
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-
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- streambuf* rdbuf() const;
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- streambuf* rdbuf(streambuf* bytebuf);
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-
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- state_type state() const;
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-
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- private:
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- streambuf* bufptr; // exposition only
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- Codecvt* cvtptr; // exposition only
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- state_type cvtstate; // exposition only
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- };
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- }
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- ```
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-
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- The class template describes a stream buffer that controls the
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- transmission of elements of type `Elem`, whose character traits are
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- described by the class `Tr`, to and from a byte stream buffer of type
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- `streambuf`. Conversion between a sequence of `Elem` values and
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- multibyte sequences is performed by an object of class `Codecvt`, which
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- shall meet the requirements of the standard code-conversion facet
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- `codecvt<Elem, char, mbstate_t>`.
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-
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- An object of this class template stores:
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-
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- - `bufptr` — a pointer to its underlying byte stream buffer
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- - `cvtptr` — a pointer to the allocated conversion object (which is
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- freed when the `wbuffer_convert` object is destroyed)
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- - `cvtstate` — a conversion state object
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-
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- ``` cpp
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- state_type state() const;
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- ```
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-
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- *Returns:* `cvtstate`.
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-
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- ``` cpp
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- streambuf* rdbuf() const;
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- ```
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-
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- *Returns:* `bufptr`.
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-
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- ``` cpp
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- streambuf* rdbuf(streambuf* bytebuf);
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- ```
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-
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- *Effects:* Stores `bytebuf` in `bufptr`.
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-
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- *Returns:* The previous value of `bufptr`.
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-
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- ``` cpp
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- explicit wbuffer_convert(
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- streambuf* bytebuf,
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- Codecvt* pcvt = new Codecvt,
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- state_type state = state_type());
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- ```
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-
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- *Requires:* `pcvt != nullptr`.
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-
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- *Effects:* The constructor constructs a stream buffer object,
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- initializes `bufptr` to `bytebuf`, initializes `cvtptr` to `pcvt`, and
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- initializes `cvtstate` to `state`.
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-
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- ``` cpp
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- ~wbuffer_convert();
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- ```
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-
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- *Effects:* The destructor shall delete `cvtptr`.
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-