--- name: "__gnu_cxx::stdio_sync_filebuf" section: "3cxx" platform: "linux" package: "libstdc++-12-doc" version: "12.4.0-5" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/__gnu_cxx::stdio_sync_filebuf/3cxx" --- # \_\_gnu\_cxx::stdio\_sync\_filebuf(3cxx) Provides a layer of compatibility for C. ## NAME \_\_gnu\_cxx::stdio\_sync\_filebuf\< \_CharT, \_Traits \> - Provides a layer of compatibility for C. ## SYNOPSIS `#include ` Inherits **std::basic\_streambuf\< \_CharT, \_Traits \>**. ### Public Types typedef \_CharT **char\_type**\ typedef traits\_type::int\_type **int\_type**\ typedef traits\_type::off\_type **off\_type**\ typedef traits\_type::pos\_type **pos\_type**\ typedef \_Traits **traits\_type**\ ### Public Member Functions **stdio\_sync\_filebuf** (std::\_\_c\_file \*\_\_f)\ **stdio\_sync\_filebuf** (**stdio\_sync\_filebuf** &&\_\_fb) noexcept\ std::\_\_c\_file \* **file** ()\ locale **getloc** () const\ Locale access. streamsize **in\_avail** ()\ Looking ahead into the stream. **stdio\_sync\_filebuf** & **operator=** (**stdio\_sync\_filebuf** &&\_\_fb) noexcept\ locale **pubimbue** (const locale &\_\_loc)\ Entry point for imbue(). int\_type **sbumpc** ()\ Getting the next character. int\_type **sgetc** ()\ Getting the next character. streamsize **sgetn** (char\_type \*\_\_s, streamsize \_\_n)\ Entry point for xsgetn. int\_type **snextc** ()\ Getting the next character. int\_type **sputbackc** (char\_type \_\_c)\ Pushing characters back into the input stream. int\_type **sputc** (char\_type \_\_c)\ Entry point for all single-character output functions. streamsize **sputn** (const char\_type \*\_\_s, streamsize \_\_n)\ Entry point for all single-character output functions. int\_type **sungetc** ()\ Moving backwards in the input stream. void **swap** (**stdio\_sync\_filebuf** &\_\_fb)\ **basic\_streambuf** \* **pubsetbuf** (char\_type \*\_\_s, streamsize \_\_n)\ Entry points for derived buffer functions. pos\_type **pubseekoff** (off\_type \_\_off, ios\_base::seekdir \_\_way, ios\_base::openmode \_\_mode=ios\_base::in\|ios\_base::out)\ Alters the stream position. pos\_type **pubseekpos** (pos\_type \_\_sp, ios\_base::openmode \_\_mode=ios\_base::in\|ios\_base::out)\ Alters the stream position. int **pubsync** ()\ Calls virtual sync function. ### Protected Member Functions void **\_\_safe\_gbump** (streamsize \_\_n)\ void **\_\_safe\_pbump** (streamsize \_\_n)\ void **gbump** (int \_\_n)\ Moving the read position. virtual void **imbue** (const locale &\_\_loc)\ Changes translations. virtual int\_type **overflow** (int\_type \_\_c=traits\_type::eof())\ Consumes data from the buffer; writes to the controlled sequence. virtual int\_type **pbackfail** (int\_type \_\_c=traits\_type::eof())\ Tries to back up the input sequence. void **pbump** (int \_\_n)\ Moving the write position. virtual pos\_type **seekoff** (off\_type, ios\_base::seekdir, ios\_base::openmode=ios\_base::in\|ios\_base::out)\ Alters the stream positions. virtual **std::streampos** **seekoff** (**std::streamoff** \_\_off, **std::ios\_base::seekdir** \_\_dir, **std::ios\_base::openmode**=**std::ios\_base::in**\|**std::ios\_base::out**)\ virtual pos\_type **seekpos** (pos\_type, ios\_base::openmode=ios\_base::in\|ios\_base::out)\ Alters the stream positions. virtual **std::streampos** **seekpos** (**std::streampos** \_\_pos, **std::ios\_base::openmode** \_\_mode=**std::ios\_base::in**\|**std::ios\_base::out**)\ virtual **basic\_streambuf**\< char\_type, \_Traits \> \* **setbuf** (char\_type \*, streamsize)\ Manipulates the buffer. void **setg** (char\_type \*\_\_gbeg, char\_type \*\_\_gnext, char\_type \*\_\_gend)\ Setting the three read area pointers. void **setp** (char\_type \*\_\_pbeg, char\_type \*\_\_pend)\ Setting the three write area pointers. virtual streamsize **showmanyc** ()\ Investigating the data available. void **swap** (**basic\_streambuf** &\_\_sb)\ virtual int **sync** ()\ Synchronizes the buffer arrays with the controlled sequences. int\_type **syncgetc** ()\ **stdio\_sync\_filebuf**\< char \>::int\_type **syncgetc** ()\ **stdio\_sync\_filebuf**\< wchar\_t \>::int\_type **syncgetc** ()\ int\_type **syncputc** (int\_type \_\_c)\ **stdio\_sync\_filebuf**\< char \>::int\_type **syncputc** (int\_type \_\_c)\ **stdio\_sync\_filebuf**\< wchar\_t \>::int\_type **syncputc** (int\_type \_\_c)\ int\_type **syncungetc** (int\_type \_\_c)\ **stdio\_sync\_filebuf**\< char \>::int\_type **syncungetc** (int\_type \_\_c)\ **stdio\_sync\_filebuf**\< wchar\_t \>::int\_type **syncungetc** (int\_type \_\_c)\ virtual int\_type **uflow** ()\ Fetches more data from the controlled sequence. virtual int\_type **underflow** ()\ Fetches more data from the controlled sequence. **std::streamsize** **xsgetn** (char \*\_\_s, **std::streamsize** \_\_n)\ virtual **std::streamsize** **xsgetn** (char\_type \*\_\_s, **std::streamsize** \_\_n)\ virtual streamsize **xsgetn** (char\_type \*\_\_s, streamsize \_\_n)\ Multiple character extraction. **std::streamsize** **xsgetn** (wchar\_t \*\_\_s, **std::streamsize** \_\_n)\ **std::streamsize** **xsputn** (const char \*\_\_s, **std::streamsize** \_\_n)\ virtual **std::streamsize** **xsputn** (const char\_type \*\_\_s, **std::streamsize** \_\_n)\ virtual streamsize **xsputn** (const char\_type \*\_\_s, streamsize \_\_n)\ Multiple character insertion. **std::streamsize** **xsputn** (const wchar\_t \*\_\_s, **std::streamsize** \_\_n)\ char\_type \* **eback** () const\ Access to the get area. char\_type \* **gptr** () const\ Access to the get area. char\_type \* **egptr** () const\ Access to the get area. char\_type \* **pbase** () const\ Access to the put area. char\_type \* **pptr** () const\ Access to the put area. char\_type \* **epptr** () const\ Access to the put area. ### Protected Attributes locale **\_M\_buf\_locale**\ Current locale setting. char\_type \* **\_M\_in\_beg**\ Start of get area. char\_type \* **\_M\_in\_cur**\ Current read area. char\_type \* **\_M\_in\_end**\ End of get area. char\_type \* **\_M\_out\_beg**\ Start of put area. char\_type \* **\_M\_out\_cur**\ Current put area. char\_type \* **\_M\_out\_end**\ End of put area. ## Detailed Description ### template\\> class \_\_gnu\_cxx::stdio\_sync\_filebuf\< \_CharT, \_Traits \>"Provides a layer of compatibility for C. This GNU extension provides extensions for working with standard C FILE\*'s. It must be instantiated by the user with the type of character used in the file stream, e.g., stdio\_filebuf\. ## Member Function Documentation ### template\ char\_type \* std::basic\_streambuf\< \_CharT, \_Traits \>::eback () const` [inline]`, ` [protected]`, ` [inherited]` Access to the get area. These functions are only available to other protected functions, including derived classes. - • eback() returns the beginning pointer for the input sequence - • gptr() returns the next pointer for the input sequence - • egptr() returns the end pointer for the input sequence ### template\ char\_type \* std::basic\_streambuf\< \_CharT, \_Traits \>::egptr () const` [inline]`, ` [protected]`, ` [inherited]` Access to the get area. These functions are only available to other protected functions, including derived classes. - • eback() returns the beginning pointer for the input sequence - • gptr() returns the next pointer for the input sequence - • egptr() returns the end pointer for the input sequence Referenced by **std::wbuffer\_convert\< \_Codecvt, \_Elem, \_Tr \>::underflow()**. ### template\ char\_type \* std::basic\_streambuf\< \_CharT, \_Traits \>::epptr () const` [inline]`, ` [protected]`, ` [inherited]` Access to the put area. These functions are only available to other protected functions, including derived classes. - • pbase() returns the beginning pointer for the output sequence - • pptr() returns the next pointer for the output sequence - • epptr() returns the end pointer for the output sequence ### template\\> std::\_\_c\_file \* \_\_gnu\_cxx::stdio\_sync\_filebuf\< \_CharT, \_Traits \>::file ()` [inline]` **Returns** The underlying FILE\*. This function can be used to access the underlying C file pointer. Note that there is no way for the library to track what you do with the file, so be careful. ### template\ void std::basic\_streambuf\< \_CharT, \_Traits \>::gbump (int \_\_n)` [inline]`, ` [protected]`, ` [inherited]` Moving the read position. **Parameters** *\_\_n* The delta by which to move. This just advances the read position without returning any data. ### template\ locale std::basic\_streambuf\< \_CharT, \_Traits \>::getloc () const` [inline]`, ` [inherited]` Locale access. **Returns** The current locale in effect. If pubimbue(loc) has been called, then the most recent `loc` is returned. Otherwise the global locale in effect at the time of construction is returned. ### template\ char\_type \* std::basic\_streambuf\< \_CharT, \_Traits \>::gptr () const` [inline]`, ` [protected]`, ` [inherited]` Access to the get area. These functions are only available to other protected functions, including derived classes. - • eback() returns the beginning pointer for the input sequence - • gptr() returns the next pointer for the input sequence - • egptr() returns the end pointer for the input sequence Referenced by **std::wbuffer\_convert\< \_Codecvt, \_Elem, \_Tr \>::underflow()**. ### template\ virtual void std::basic\_streambuf\< \_CharT, \_Traits \>::imbue (const locale & \_\_loc)` [inline]`, ` [protected]`, ` [virtual]`, ` [inherited]` Changes translations. **Parameters** *\_\_loc* A new locale. Translations done during I/O which depend on the current locale are changed by this call. The standard adds, *Between invocations of this function a class derived from streambuf can safely cache results of calls to locale functions and to members of facets so obtained.* **Note** Base class version does nothing. Reimplemented in **std::basic\_filebuf\< \_CharT, \_Traits \>**, **std::basic\_filebuf\< \_CharT, encoding\_char\_traits\< \_CharT \> \>**, **std::basic\_filebuf\< \_CharT, std::char\_traits\< \_CharT \> \>**, and **std::basic\_filebuf\< char\_type, traits\_type \>**. ### template\ streamsize std::basic\_streambuf\< \_CharT, \_Traits \>::in\_avail ()` [inline]`, ` [inherited]` Looking ahead into the stream. **Returns** The number of characters available. If a read position is available, returns the number of characters available for reading before the buffer must be refilled. Otherwise returns the derived `showmanyc()`. ### template\\> virtual int\_type \_\_gnu\_cxx::stdio\_sync\_filebuf\< \_CharT, \_Traits \>::overflow (int\_type \_\_c = `traits_type::eof()`)` [inline]`, ` [protected]`, ` [virtual]` Consumes data from the buffer; writes to the controlled sequence. **Parameters** *\_\_c* An additional character to consume. **Returns** eof() to indicate failure, something else (usually *\_\_c*, or not\_eof()) Informally, this function is called when the output buffer is full (or does not exist, as buffering need not actually be done). If a buffer exists, it is *consumed*, with *some effect* on the controlled sequence. (Typically, the buffer is written out to the sequence verbatim.) In either case, the character *c* is also written out, if *\_\_c* is not `eof()`. For a formal definition of this function, see a good text such as Langer & Kreft, or \[27.5.2.4.5\]/3-7. A functioning output streambuf can be created by overriding only this function (no buffer area will be used). **Note** Base class version does nothing, returns eof(). Reimplemented from **std::basic\_streambuf\< \_CharT, \_Traits \>**. ### template\\> virtual int\_type \_\_gnu\_cxx::stdio\_sync\_filebuf\< \_CharT, \_Traits \>::pbackfail (int\_type \_\_c = `traits_type::eof()`)` [inline]`, ` [protected]`, ` [virtual]` Tries to back up the input sequence. **Parameters** *\_\_c* The character to be inserted back into the sequence. **Returns** eof() on failure, *some other value* on success **Postcondition** The constraints of `gptr()`, `eback()`, and `pptr()` are the same as for `underflow()`. **Note** Base class version does nothing, returns eof(). Reimplemented from **std::basic\_streambuf\< \_CharT, \_Traits \>**. ### template\ char\_type \* std::basic\_streambuf\< \_CharT, \_Traits \>::pbase () const` [inline]`, ` [protected]`, ` [inherited]` Access to the put area. These functions are only available to other protected functions, including derived classes. - • pbase() returns the beginning pointer for the output sequence - • pptr() returns the next pointer for the output sequence - • epptr() returns the end pointer for the output sequence ### template\ void std::basic\_streambuf\< \_CharT, \_Traits \>::pbump (int \_\_n)` [inline]`, ` [protected]`, ` [inherited]` Moving the write position. **Parameters** *\_\_n* The delta by which to move. This just advances the write position without returning any data. ### template\ char\_type \* std::basic\_streambuf\< \_CharT, \_Traits \>::pptr () const` [inline]`, ` [protected]`, ` [inherited]` Access to the put area. These functions are only available to other protected functions, including derived classes. - • pbase() returns the beginning pointer for the output sequence - • pptr() returns the next pointer for the output sequence - • epptr() returns the end pointer for the output sequence ### template\ locale std::basic\_streambuf\< \_CharT, \_Traits \>::pubimbue (const locale & \_\_loc)` [inline]`, ` [inherited]` Entry point for imbue(). **Parameters** *\_\_loc* The new locale. **Returns** The previous locale. Calls the derived imbue(\_\_loc). ### template\ pos\_type std::basic\_streambuf\< \_CharT, \_Traits \>::pubseekoff (off\_type \_\_off, ios\_base::seekdir \_\_way, ios\_base::openmode \_\_mode = ios\_base::in` | `ios\_base::out)` [inline]`, ` [inherited]` Alters the stream position. **Parameters** *\_\_off* Offset. \ *\_\_way* Value for ios\_base::seekdir. \ *\_\_mode* Value for ios\_base::openmode. Calls virtual seekoff function. ### template\ pos\_type std::basic\_streambuf\< \_CharT, \_Traits \>::pubseekpos (pos\_type \_\_sp, ios\_base::openmode \_\_mode = ios\_base::in` | `ios\_base::out)` [inline]`, ` [inherited]` Alters the stream position. **Parameters** *\_\_sp* Position \ *\_\_mode* Value for ios\_base::openmode. Calls virtual seekpos function. ### template\ basic\_streambuf \* std::basic\_streambuf\< \_CharT, \_Traits \>::pubsetbuf (char\_type \* \_\_s, streamsize \_\_n)` [inline]`, ` [inherited]` Entry points for derived buffer functions. The public versions of `pubfoo` dispatch to the protected derived `foo` member functions, passing the arguments (if any) and returning the result unchanged. ### template\ int std::basic\_streambuf\< \_CharT, \_Traits \>::pubsync ()` [inline]`, ` [inherited]` Calls virtual sync function. ### template\ int\_type std::basic\_streambuf\< \_CharT, \_Traits \>::sbumpc ()` [inline]`, ` [inherited]` Getting the next character. **Returns** The next character, or eof. If the input read position is available, returns that character and increments the read pointer, otherwise calls and returns `uflow()`. ### template\ virtual pos\_type std::basic\_streambuf\< \_CharT, \_Traits \>::seekoff (off\_type, ios\_base::seekdir, ios\_base::openmode = ios\_base::in` | `ios\_base::out)` [inline]`, ` [protected]`, ` [virtual]`, ` [inherited]` Alters the stream positions. Each derived class provides its own appropriate behavior. **Note** Base class version does nothing, returns a `pos_type` that represents an invalid stream position. Reimplemented in **std::basic\_filebuf\< \_CharT, \_Traits \>**, **std::basic\_filebuf\< \_CharT, encoding\_char\_traits\< \_CharT \> \>**, **std::basic\_filebuf\< \_CharT, std::char\_traits\< \_CharT \> \>**, **std::basic\_filebuf\< char\_type, traits\_type \>**, and **std::basic\_stringbuf\< \_CharT, \_Traits, \_Alloc \>**. ### template\ virtual pos\_type std::basic\_streambuf\< \_CharT, \_Traits \>::seekpos (pos\_type, ios\_base::openmode = ios\_base::in` | `ios\_base::out)` [inline]`, ` [protected]`, ` [virtual]`, ` [inherited]` Alters the stream positions. Each derived class provides its own appropriate behavior. **Note** Base class version does nothing, returns a `pos_type` that represents an invalid stream position. Reimplemented in **std::basic\_filebuf\< \_CharT, \_Traits \>**, **std::basic\_filebuf\< \_CharT, encoding\_char\_traits\< \_CharT \> \>**, **std::basic\_filebuf\< \_CharT, std::char\_traits\< \_CharT \> \>**, **std::basic\_filebuf\< char\_type, traits\_type \>**, and **std::basic\_stringbuf\< \_CharT, \_Traits, \_Alloc \>**. ### template\ virtual basic\_streambuf\< char\_type, \_Traits \> \* std::basic\_streambuf\< \_CharT, \_Traits \>::setbuf (char\_type \*, streamsize)` [inline]`, ` [protected]`, ` [virtual]`, ` [inherited]` Manipulates the buffer. Each derived class provides its own appropriate behavior. See the next-to-last paragraph of https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html#io.streambuf.buffering for more on this function. **Note** Base class version does nothing, returns `this`. Reimplemented in **std::basic\_filebuf\< \_CharT, \_Traits \>**, **std::basic\_filebuf\< \_CharT, encoding\_char\_traits\< \_CharT \> \>**, **std::basic\_filebuf\< \_CharT, std::char\_traits\< \_CharT \> \>**, **std::basic\_filebuf\< char\_type, traits\_type \>**, and **std::basic\_stringbuf\< \_CharT, \_Traits, \_Alloc \>**. ### template\ void std::basic\_streambuf\< \_CharT, \_Traits \>::setg (char\_type \* \_\_gbeg, char\_type \* \_\_gnext, char\_type \* \_\_gend)` [inline]`, ` [protected]`, ` [inherited]` Setting the three read area pointers. **Parameters** *\_\_gbeg* A pointer. \ *\_\_gnext* A pointer. \ *\_\_gend* A pointer. **Postcondition** *\_\_gbeg* == `eback()`, *\_\_gnext* == `gptr()`, and *\_\_gend* == `egptr()` Referenced by **std::wbuffer\_convert\< \_Codecvt, \_Elem, \_Tr \>::wbuffer\_convert()**. ### template\ void std::basic\_streambuf\< \_CharT, \_Traits \>::setp (char\_type \* \_\_pbeg, char\_type \* \_\_pend)` [inline]`, ` [protected]`, ` [inherited]` Setting the three write area pointers. **Parameters** *\_\_pbeg* A pointer. \ *\_\_pend* A pointer. **Postcondition** *\_\_pbeg* == `pbase()`, *\_\_pbeg* == `pptr()`, and *\_\_pend* == `epptr()` Referenced by **std::wbuffer\_convert\< \_Codecvt, \_Elem, \_Tr \>::wbuffer\_convert()**. ### template\ int\_type std::basic\_streambuf\< \_CharT, \_Traits \>::sgetc ()` [inline]`, ` [inherited]` Getting the next character. **Returns** The next character, or eof. If the input read position is available, returns that character, otherwise calls and returns `underflow()`. Does not move the read position after fetching the character. ### template\ streamsize std::basic\_streambuf\< \_CharT, \_Traits \>::sgetn (char\_type \* \_\_s, streamsize \_\_n)` [inline]`, ` [inherited]` Entry point for xsgetn. **Parameters** *\_\_s* A buffer area. \ *\_\_n* A count. Returns xsgetn(\_\_s,\_\_n). The effect is to fill *\_\_s*\[0\] through *\_\_s*\[\_\_n-1\] with characters from the input sequence, if possible. ### template\ virtual streamsize std::basic\_streambuf\< \_CharT, \_Traits \>::showmanyc ()` [inline]`, ` [protected]`, ` [virtual]`, ` [inherited]` Investigating the data available. **Returns** An estimate of the number of characters available in the input sequence, or -1. *If it returns a positive value, then successive calls to* `underflow()` *will not return* `traits::eof()` *until at least that number of characters have been supplied. If* `showmanyc()` *returns -1, then calls to* `underflow()` *or* `uflow()` *will fail.*` [27.5.2.4.3]/1` **Note** `Base class version does nothing, returns zero. ` `The standard adds that `*the intention is not only that the calls \[to underflow or uflow\] will not return* `eof()` *but that they will return immediately.*` ` `The standard adds that `*the morphemes of* `showmanyc` *are* **es-how-many-see***, not* **show-manic***.* **Reimplemented in std::basic\_filebuf\< \_CharT, \_Traits \>, std::basic\_filebuf\< \_CharT, encoding\_char\_traits\< \_CharT \> \>, std::basic\_filebuf\< \_CharT, std::char\_traits\< \_CharT \> \>, std::basic\_filebuf\< char\_type, traits\_type \>, and std::basic\_stringbuf\< \_CharT, \_Traits, \_Alloc \>.** ### template\ int\_type std::basic\_streambuf\< \_CharT, \_Traits \>::snextc ()` [inline]`, ` [inherited]` **Getting the next character.** **Returns** **The next character, or eof.** **Calls** `sbumpc()`**, and if that function returns** `traits::eof()`**, so does this function. Otherwise,** `sgetc()`**.** ### template\ int\_type std::basic\_streambuf\< \_CharT, \_Traits \>::sputbackc (char\_type \_\_c)` [inline]`, ` [inherited]` **Pushing characters back into the input stream.** **Parameters** *\_\_c* **The character to push back.** **Returns** **The previous character, if possible.** **Similar to sungetc(), but** *\_\_c* **is pushed onto the stream instead of** *the previous character.* **If successful, the next character fetched from the input stream will be** *\_\_c***.** ### template\ int\_type std::basic\_streambuf\< \_CharT, \_Traits \>::sputc (char\_type \_\_c)` [inline]`, ` [inherited]` **Entry point for all single-character output functions.** **Parameters** *\_\_c* **A character to output.** **Returns** *\_\_c***, if possible.** **One of two public output functions.** **If a write position is available for the output sequence (i.e., the buffer is not full), stores** *\_\_c* **in that position, increments the position, and returns** `traits::to_int_type(__c)`**. If a write position is not available, returns** `overflow(__c)`**.** **Referenced by std::wbuffer\_convert\< \_Codecvt, \_Elem, \_Tr \>::overflow().** ### template\ streamsize std::basic\_streambuf\< \_CharT, \_Traits \>::sputn (const char\_type \* \_\_s, streamsize \_\_n)` [inline]`, ` [inherited]` **Entry point for all single-character output functions.** **Parameters** *\_\_s* **A buffer read area.** \ *\_\_n* **A count.** **One of two public output functions.** **Returns xsputn(\_\_s,\_\_n). The effect is to write** *\_\_s***\[0\] through** *\_\_s***\[\_\_n-1\] to the output sequence, if possible.** ### template\ int\_type std::basic\_streambuf\< \_CharT, \_Traits \>::sungetc ()` [inline]`, ` [inherited]` **Moving backwards in the input stream.** **Returns** **The previous character, if possible.** **If a putback position is available, this function decrements the input pointer and returns that character. Otherwise, calls and returns pbackfail(). The effect is to** *unget* **the last character** *gotten***.** ### template\\> virtual int \_\_gnu\_cxx::stdio\_sync\_filebuf\< \_CharT, \_Traits \>::sync ()` [inline]`, ` [protected]`, ` [virtual]` **Synchronizes the buffer arrays with the controlled sequences.** **Returns** **-1 on failure.** **Each derived class provides its own appropriate behavior, including the definition of** *failure***.** **Note** **Base class version does nothing, returns zero.** **Reimplemented from std::basic\_streambuf\< \_CharT, \_Traits \>.** ### template\\> virtual int\_type \_\_gnu\_cxx::stdio\_sync\_filebuf\< \_CharT, \_Traits \>::uflow ()` [inline]`, ` [protected]`, ` [virtual]` **Fetches more data from the controlled sequence.** **Returns** **The first character from the** *pending sequence***.** **Informally, this function does the same thing as** `underflow()`**, and in fact is required to call that function. It also returns the new character, like** `underflow()` **does. However, this function also moves the read position forward by one.** **Reimplemented from std::basic\_streambuf\< \_CharT, \_Traits \>.** ### template\\> virtual int\_type \_\_gnu\_cxx::stdio\_sync\_filebuf\< \_CharT, \_Traits \>::underflow ()` [inline]`, ` [protected]`, ` [virtual]` **Fetches more data from the controlled sequence.** **Returns** **The first character from the** *pending sequence***.** **Informally, this function is called when the input buffer is exhausted (or does not exist, as buffering need not actually be done). If a buffer exists, it is** *refilled***. In either case, the next available character is returned, or** `traits::eof()` **to indicate a null pending sequence.** **For a formal definition of the pending sequence, see a good text such as Langer & Kreft, or \[27.5.2.4.3\]/7-14.** **A functioning input streambuf can be created by overriding only this function (no buffer area will be used). For an example, see https://gcc.gnu.org/onlinedocs/libstdc++/manual/streambufs.html** **Note** **Base class version does nothing, returns eof().** **Reimplemented from std::basic\_streambuf\< \_CharT, \_Traits \>.** ### template\ streamsize std::basic\_streambuf\< \_CharT, \_Traits \>::xsgetn (char\_type \* \_\_s, streamsize \_\_n)` [protected]`, ` [virtual]`, ` [inherited]` **Multiple character extraction.** **Parameters** *\_\_s* **A buffer area.** \ *\_\_n* **Maximum number of characters to assign.** **Returns** **The number of characters assigned.** **Fills** *\_\_s***\[0\] through** *\_\_s***\[\_\_n-1\] with characters from the input sequence, as if by** `sbumpc()`**. Stops when either** *\_\_n* **characters have been copied, or when** `traits::eof()` **would be copied.** **It is expected that derived classes provide a more efficient implementation by overriding this definition.** **Reimplemented in std::basic\_filebuf\< \_CharT, \_Traits \>, std::basic\_filebuf\< \_CharT, encoding\_char\_traits\< \_CharT \> \>, std::basic\_filebuf\< \_CharT, std::char\_traits\< \_CharT \> \>, and std::basic\_filebuf\< char\_type, traits\_type \>.** **References std::min().** ### template\ streamsize std::basic\_streambuf\< \_CharT, \_Traits \>::xsputn (const char\_type \* \_\_s, streamsize \_\_n)` [protected]`, ` [virtual]`, ` [inherited]` **Multiple character insertion.** **Parameters** *\_\_s* **A buffer area.** \ *\_\_n* **Maximum number of characters to write.** **Returns** **The number of characters written.** **Writes** *\_\_s***\[0\] through** *\_\_s***\[\_\_n-1\] to the output sequence, as if by** `sputc()`**. Stops when either** *n* **characters have been copied, or when** `sputc()` **would return** `traits::eof()`**.** **It is expected that derived classes provide a more efficient implementation by overriding this definition.** **Reimplemented in std::basic\_filebuf\< \_CharT, \_Traits \>, std::basic\_filebuf\< \_CharT, encoding\_char\_traits\< \_CharT \> \>, std::basic\_filebuf\< \_CharT, std::char\_traits\< \_CharT \> \>, and std::basic\_filebuf\< char\_type, traits\_type \>.** **References std::min().** ## Member Data Documentation ### template\ locale std::basic\_streambuf\< \_CharT, \_Traits \>::\_M\_buf\_locale` [protected]`, ` [inherited]` **Current locale setting.** **Referenced by std::basic\_filebuf\< \_CharT, \_Traits \>::basic\_filebuf().** ### template\ char\_type\* std::basic\_streambuf\< \_CharT, \_Traits \>::\_M\_in\_beg` [protected]`, ` [inherited]` **Start of get area.** ### template\ char\_type\* std::basic\_streambuf\< \_CharT, \_Traits \>::\_M\_in\_cur` [protected]`, ` [inherited]` **Current read area.** ### template\ char\_type\* std::basic\_streambuf\< \_CharT, \_Traits \>::\_M\_in\_end` [protected]`, ` [inherited]` **End of get area.** ### template\ char\_type\* std::basic\_streambuf\< \_CharT, \_Traits \>::\_M\_out\_beg` [protected]`, ` [inherited]` **Start of put area.** ### template\ char\_type\* std::basic\_streambuf\< \_CharT, \_Traits \>::\_M\_out\_cur` [protected]`, ` [inherited]` **Current put area.** ### template\ char\_type\* std::basic\_streambuf\< \_CharT, \_Traits \>::\_M\_out\_end` [protected]`, ` [inherited]` **End of put area.** ## Author **Generated automatically by Doxygen for libstdc++ from the source code.**