// Stream buffer classes -*- C++ -*- // Copyright (C) 1997-2022 Free Software Foundation, Inc. // // This file is part of the GNU ISO C++ Library. This library is free // software; you can redistribute it and/or modify it under the // terms of the GNU General Public License as published by the // Free Software Foundation; either version 3, or (at your option) // any later version. // This library is distributed in the hope that it will be useful, // but WITHOUT ANY WARRANTY; without even the implied warranty of // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the // GNU General Public License for more details. // Under Section 7 of GPL version 3, you are granted additional // permissions described in the GCC Runtime Library Exception, version // 3.1, as published by the Free Software Foundation. // You should have received a copy of the GNU General Public License and // a copy of the GCC Runtime Library Exception along with this program; // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see // . /** @file include/streambuf * This is a Standard C++ Library header. */ // // ISO C++ 14882: 27.5 Stream buffers // #ifndef _GLIBXX_STREAMBUF #define _GLIBXX_STREAMBUF 1 #pragma GCC system_header #include #include #include #include #include #include namespace std _GLIBCXX_VISIBILITY(default) { _GLIBCXX_BEGIN_NAMESPACE_VERSION #define _IsUnused __attribute__ ((__unused__)) template streamsize __copy_streambufs_eof(basic_streambuf<_CharT, _Traits>*, basic_streambuf<_CharT, _Traits>*, bool&); /** * @brief The actual work of input and output (interface). * @ingroup io * * @tparam _CharT Type of character stream. * @tparam _Traits Traits for character type, defaults to * char_traits<_CharT>. * * This is a base class. Derived stream buffers each control a * pair of character sequences: one for input, and one for output. * * Section [27.5.1] of the standard describes the requirements and * behavior of stream buffer classes. That section (three paragraphs) * is reproduced here, for simplicity and accuracy. * * -# Stream buffers can impose various constraints on the sequences * they control. Some constraints are: * - The controlled input sequence can be not readable. * - The controlled output sequence can be not writable. * - The controlled sequences can be associated with the contents of * other representations for character sequences, such as external * files. * - The controlled sequences can support operations @e directly to or * from associated sequences. * - The controlled sequences can impose limitations on how the * program can read characters from a sequence, write characters to * a sequence, put characters back into an input sequence, or alter * the stream position. * . * -# Each sequence is characterized by three pointers which, if non-null, * all point into the same @c charT array object. The array object * represents, at any moment, a (sub)sequence of characters from the * sequence. Operations performed on a sequence alter the values * stored in these pointers, perform reads and writes directly to or * from associated sequences, and alter the stream position and * conversion state as needed to maintain this subsequence relationship. * The three pointers are: * - the beginning pointer, or lowest element address in the * array (called @e xbeg here); * - the next pointer, or next element address that is a * current candidate for reading or writing (called @e xnext here); * - the end pointer, or first element address beyond the * end of the array (called @e xend here). * . * -# The following semantic constraints shall always apply for any set * of three pointers for a sequence, using the pointer names given * immediately above: * - If @e xnext is not a null pointer, then @e xbeg and @e xend shall * also be non-null pointers into the same @c charT array, as * described above; otherwise, @e xbeg and @e xend shall also be null. * - If @e xnext is not a null pointer and @e xnext < @e xend for an * output sequence, then a write position is available. * In this case, @e *xnext shall be assignable as the next element * to write (to put, or to store a character value, into the sequence). * - If @e xnext is not a null pointer and @e xbeg < @e xnext for an * input sequence, then a putback position is available. * In this case, @e xnext[-1] shall have a defined value and is the * next (preceding) element to store a character that is put back * into the input sequence. * - If @e xnext is not a null pointer and @e xnext< @e xend for an * input sequence, then a read position is available. * In this case, @e *xnext shall have a defined value and is the * next element to read (to get, or to obtain a character value, * from the sequence). */ template class basic_streambuf { public: ///@{ /** * These are standard types. They permit a standardized way of * referring to names of (or names dependent on) the template * parameters, which are specific to the implementation. */ typedef _CharT char_type; typedef _Traits traits_type; typedef typename traits_type::int_type int_type; typedef typename traits_type::pos_type pos_type; typedef typename traits_type::off_type off_type; ///@} ///@{ /// This is a non-standard type. typedef basic_streambuf __streambuf_type; ///@} friend class basic_ios; friend class basic_istream; friend class basic_ostream; friend class istreambuf_iterator; friend class ostreambuf_iterator; friend streamsize __copy_streambufs_eof<>(basic_streambuf*, basic_streambuf*, bool&); template friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value, _CharT2*>::__type __copy_move_a2(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>, _CharT2*); template friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value, istreambuf_iterator<_CharT2> >::__type find(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>, const _CharT2&); template friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value, void>::__type advance(istreambuf_iterator<_CharT2>&, _Distance); friend void __istream_extract(istream&, char*, streamsize); template friend basic_istream<_CharT2, _Traits2>& operator>>(basic_istream<_CharT2, _Traits2>&, basic_string<_CharT2, _Traits2, _Alloc>&); template friend basic_istream<_CharT2, _Traits2>& getline(basic_istream<_CharT2, _Traits2>&, basic_string<_CharT2, _Traits2, _Alloc>&, _CharT2); protected: /* * This is based on _IO_FILE, just reordered to be more consistent, * and is intended to be the most minimal abstraction for an * internal buffer. * - get == input == read * - put == output == write */ 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. /// Current locale setting. locale _M_buf_locale; public: /// Destructor deallocates no buffer space. virtual ~basic_streambuf() { } // [27.5.2.2.1] locales /** * @brief Entry point for imbue(). * @param __loc The new locale. * @return The previous locale. * * Calls the derived imbue(__loc). */ locale pubimbue(const locale& __loc) { locale __tmp(this->getloc()); this->imbue(__loc); _M_buf_locale = __loc; return __tmp; } /** * @brief Locale access. * @return The current locale in effect. * * If pubimbue(loc) has been called, then the most recent @c loc * is returned. Otherwise the global locale in effect at the time * of construction is returned. */ locale getloc() const { return _M_buf_locale; } // [27.5.2.2.2] buffer management and positioning ///@{ /** * @brief Entry points for derived buffer functions. * * The public versions of @c pubfoo dispatch to the protected * derived @c foo member functions, passing the arguments (if any) * and returning the result unchanged. */ basic_streambuf* pubsetbuf(char_type* __s, streamsize __n) { return this->setbuf(__s, __n); } /** * @brief Alters the stream position. * @param __off Offset. * @param __way Value for ios_base::seekdir. * @param __mode Value for ios_base::openmode. * * Calls virtual seekoff function. */ pos_type pubseekoff(off_type __off, ios_base::seekdir __way, ios_base::openmode __mode = ios_base::in | ios_base::out) { return this->seekoff(__off, __way, __mode); } /** * @brief Alters the stream position. * @param __sp Position * @param __mode Value for ios_base::openmode. * * Calls virtual seekpos function. */ pos_type pubseekpos(pos_type __sp, ios_base::openmode __mode = ios_base::in | ios_base::out) { return this->seekpos(__sp, __mode); } /** * @brief Calls virtual sync function. */ int pubsync() { return this->sync(); } ///@} // [27.5.2.2.3] get area /** * @brief Looking ahead into the stream. * @return 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 @c showmanyc(). */ streamsize in_avail() { const streamsize __ret = this->egptr() - this->gptr(); return __ret ? __ret : this->showmanyc(); } /** * @brief Getting the next character. * @return The next character, or eof. * * Calls @c sbumpc(), and if that function returns * @c traits::eof(), so does this function. Otherwise, @c sgetc(). */ int_type snextc() { int_type __ret = traits_type::eof(); if (__builtin_expect(!traits_type::eq_int_type(this->sbumpc(), __ret), true)) __ret = this->sgetc(); return __ret; } /** * @brief Getting the next character. * @return The next character, or eof. * * If the input read position is available, returns that character * and increments the read pointer, otherwise calls and returns * @c uflow(). */ int_type sbumpc() { int_type __ret; if (__builtin_expect(this->gptr() < this->egptr(), true)) { __ret = traits_type::to_int_type(*this->gptr()); this->gbump(1); } else __ret = this->uflow(); return __ret; } /** * @brief Getting the next character. * @return The next character, or eof. * * If the input read position is available, returns that character, * otherwise calls and returns @c underflow(). Does not move the * read position after fetching the character. */ int_type sgetc() { int_type __ret; if (__builtin_expect(this->gptr() < this->egptr(), true)) __ret = traits_type::to_int_type(*this->gptr()); else __ret = this->underflow(); return __ret; } /** * @brief Entry point for xsgetn. * @param __s A buffer area. * @param __n A count. * * Returns xsgetn(__s,__n). The effect is to fill @a __s[0] through * @a __s[__n-1] with characters from the input sequence, if possible. */ streamsize sgetn(char_type* __s, streamsize __n) { return this->xsgetn(__s, __n); } // [27.5.2.2.4] putback /** * @brief Pushing characters back into the input stream. * @param __c The character to push back. * @return The previous character, if possible. * * Similar to sungetc(), but @a __c is pushed onto the stream * instead of the previous character. If successful, * the next character fetched from the input stream will be @a * __c. */ int_type sputbackc(char_type __c) { int_type __ret; const bool __testpos = this->eback() < this->gptr(); if (__builtin_expect(!__testpos || !traits_type::eq(__c, this->gptr()[-1]), false)) __ret = this->pbackfail(traits_type::to_int_type(__c)); else { this->gbump(-1); __ret = traits_type::to_int_type(*this->gptr()); } return __ret; } /** * @brief Moving backwards in the input stream. * @return 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 @a unget * the last character @a gotten. */ int_type sungetc() { int_type __ret; if (__builtin_expect(this->eback() < this->gptr(), true)) { this->gbump(-1); __ret = traits_type::to_int_type(*this->gptr()); } else __ret = this->pbackfail(); return __ret; } // [27.5.2.2.5] put area /** * @brief Entry point for all single-character output functions. * @param __c A character to output. * @return @a __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 @a __c in that position, increments * the position, and returns @c traits::to_int_type(__c). If a write * position is not available, returns @c overflow(__c). */ int_type sputc(char_type __c) { int_type __ret; if (__builtin_expect(this->pptr() < this->epptr(), true)) { *this->pptr() = __c; this->pbump(1); __ret = traits_type::to_int_type(__c); } else __ret = this->overflow(traits_type::to_int_type(__c)); return __ret; } /** * @brief Entry point for all single-character output functions. * @param __s A buffer read area. * @param __n A count. * * One of two public output functions. * * * Returns xsputn(__s,__n). The effect is to write @a __s[0] through * @a __s[__n-1] to the output sequence, if possible. */ streamsize sputn(const char_type* __s, streamsize __n) { return this->xsputn(__s, __n); } protected: /** * @brief Base constructor. * * Only called from derived constructors, and sets up all the * buffer data to zero, including the pointers described in the * basic_streambuf class description. Note that, as a result, * - the class starts with no read nor write positions available, * - this is not an error */ basic_streambuf() : _M_in_beg(0), _M_in_cur(0), _M_in_end(0), _M_out_beg(0), _M_out_cur(0), _M_out_end(0), _M_buf_locale(locale()) { } // [27.5.2.3.1] get area access ///@{ /** * @brief 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 */ char_type* eback() const { return _M_in_beg; } char_type* gptr() const { return _M_in_cur; } char_type* egptr() const { return _M_in_end; } ///@} /** * @brief Moving the read position. * @param __n The delta by which to move. * * This just advances the read position without returning any data. */ void gbump(int __n) { _M_in_cur += __n; } /** * @brief Setting the three read area pointers. * @param __gbeg A pointer. * @param __gnext A pointer. * @param __gend A pointer. * @post @a __gbeg == @c eback(), @a __gnext == @c gptr(), and * @a __gend == @c egptr() */ void setg(char_type* __gbeg, char_type* __gnext, char_type* __gend) { _M_in_beg = __gbeg; _M_in_cur = __gnext; _M_in_end = __gend; } // [27.5.2.3.2] put area access ///@{ /** * @brief 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 */ char_type* pbase() const { return _M_out_beg; } char_type* pptr() const { return _M_out_cur; } char_type* epptr() const { return _M_out_end; } ///@} /** * @brief Moving the write position. * @param __n The delta by which to move. * * This just advances the write position without returning any data. */ void pbump(int __n) { _M_out_cur += __n; } /** * @brief Setting the three write area pointers. * @param __pbeg A pointer. * @param __pend A pointer. * @post @a __pbeg == @c pbase(), @a __pbeg == @c pptr(), and * @a __pend == @c epptr() */ void setp(char_type* __pbeg, char_type* __pend) { _M_out_beg = _M_out_cur = __pbeg; _M_out_end = __pend; } // [27.5.2.4] virtual functions // [27.5.2.4.1] locales /** * @brief Changes translations. * @param __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. */ virtual void imbue(const locale& __loc _IsUnused) { } // [27.5.2.4.2] buffer management and positioning /** * @brief 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 @c this. */ virtual basic_streambuf* setbuf(char_type*, streamsize) { return this; } /** * @brief Alters the stream positions. * * Each derived class provides its own appropriate behavior. * @note Base class version does nothing, returns a @c pos_type * that represents an invalid stream position. */ virtual pos_type seekoff(off_type, ios_base::seekdir, ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out) { return pos_type(off_type(-1)); } /** * @brief Alters the stream positions. * * Each derived class provides its own appropriate behavior. * @note Base class version does nothing, returns a @c pos_type * that represents an invalid stream position. */ virtual pos_type seekpos(pos_type, ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out) { return pos_type(off_type(-1)); } /** * @brief Synchronizes the buffer arrays with the controlled sequences. * @return -1 on failure. * * Each derived class provides its own appropriate behavior, * including the definition of @a failure. * @note Base class version does nothing, returns zero. */ virtual int sync() { return 0; } // [27.5.2.4.3] get area /** * @brief Investigating the data available. * @return An estimate of the number of characters available in the * input sequence, or -1. * * If it returns a positive value, then successive calls to * @c underflow() will not return @c traits::eof() until at * least that number of characters have been supplied. If @c * showmanyc() returns -1, then calls to @c underflow() or @c * uflow() will fail. [27.5.2.4.3]/1 * * @note Base class version does nothing, returns zero. * @note The standard adds that the intention is not only that the * calls [to underflow or uflow] will not return @c eof() but * that they will return immediately. * @note The standard adds that the morphemes of @c showmanyc are * @b es-how-many-see, not @b show-manic. */ virtual streamsize showmanyc() { return 0; } /** * @brief Multiple character extraction. * @param __s A buffer area. * @param __n Maximum number of characters to assign. * @return The number of characters assigned. * * Fills @a __s[0] through @a __s[__n-1] with characters from the input * sequence, as if by @c sbumpc(). Stops when either @a __n characters * have been copied, or when @c traits::eof() would be copied. * * It is expected that derived classes provide a more efficient * implementation by overriding this definition. */ virtual streamsize xsgetn(char_type* __s, streamsize __n); /** * @brief Fetches more data from the controlled sequence. * @return 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 @a refilled. In either case, the * next available character is returned, or @c 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(). */ virtual int_type underflow() { return traits_type::eof(); } /** * @brief Fetches more data from the controlled sequence. * @return The first character from the pending sequence. * * Informally, this function does the same thing as @c underflow(), * and in fact is required to call that function. It also returns * the new character, like @c underflow() does. However, this * function also moves the read position forward by one. */ virtual int_type uflow() { int_type __ret = traits_type::eof(); const bool __testeof = traits_type::eq_int_type(this->underflow(), __ret); if (!__testeof) { __ret = traits_type::to_int_type(*this->gptr()); this->gbump(1); } return __ret; } // [27.5.2.4.4] putback /** * @brief Tries to back up the input sequence. * @param __c The character to be inserted back into the sequence. * @return eof() on failure, some other value on success * @post The constraints of @c gptr(), @c eback(), and @c pptr() * are the same as for @c underflow(). * * @note Base class version does nothing, returns eof(). */ virtual int_type pbackfail(int_type __c _IsUnused = traits_type::eof()) { return traits_type::eof(); } // Put area: /** * @brief Multiple character insertion. * @param __s A buffer area. * @param __n Maximum number of characters to write. * @return The number of characters written. * * Writes @a __s[0] through @a __s[__n-1] to the output sequence, as if * by @c sputc(). Stops when either @a n characters have been * copied, or when @c sputc() would return @c traits::eof(). * * It is expected that derived classes provide a more efficient * implementation by overriding this definition. */ virtual streamsize xsputn(const char_type* __s, streamsize __n); /** * @brief Consumes data from the buffer; writes to the * controlled sequence. * @param __c An additional character to consume. * @return eof() to indicate failure, something else (usually * @a __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 @a consumed, with * some effect on the controlled sequence. * (Typically, the buffer is written out to the sequence * verbatim.) In either case, the character @a c is also * written out, if @a __c is not @c 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(). */ virtual int_type overflow(int_type __c _IsUnused = traits_type::eof()) { return traits_type::eof(); } #if _GLIBCXX_USE_DEPRECATED && __cplusplus <= 201402L // Annex D.6 (removed in C++17) public: /** * @brief Tosses a character. * * Advances the read pointer, ignoring the character that would have * been read. * * See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html */ _GLIBCXX_DEPRECATED_SUGGEST("std::basic_streambuf::sbumpc") void stossc() { if (this->gptr() < this->egptr()) this->gbump(1); else this->uflow(); } #endif // Also used by specializations for char and wchar_t in src. void __safe_gbump(streamsize __n) { _M_in_cur += __n; } void __safe_pbump(streamsize __n) { _M_out_cur += __n; } #if __cplusplus < 201103L private: #else protected: #endif basic_streambuf(const basic_streambuf&); basic_streambuf& operator=(const basic_streambuf&); #if __cplusplus >= 201103L void swap(basic_streambuf& __sb) { std::swap(_M_in_beg, __sb._M_in_beg); std::swap(_M_in_cur, __sb._M_in_cur); std::swap(_M_in_end, __sb._M_in_end); std::swap(_M_out_beg, __sb._M_out_beg); std::swap(_M_out_cur, __sb._M_out_cur); std::swap(_M_out_end, __sb._M_out_end); std::swap(_M_buf_locale, __sb._M_buf_locale); } #endif }; #if __cplusplus >= 201103L template std::basic_streambuf<_CharT, _Traits>:: basic_streambuf(const basic_streambuf&) = default; template std::basic_streambuf<_CharT, _Traits>& std::basic_streambuf<_CharT, _Traits>:: operator=(const basic_streambuf&) = default; #endif // Explicit specialization declarations, defined in src/streambuf.cc. template<> streamsize __copy_streambufs_eof(basic_streambuf* __sbin, basic_streambuf* __sbout, bool& __ineof); #ifdef _GLIBCXX_USE_WCHAR_T template<> streamsize __copy_streambufs_eof(basic_streambuf* __sbin, basic_streambuf* __sbout, bool& __ineof); #endif #undef _IsUnused _GLIBCXX_END_NAMESPACE_VERSION } // namespace #include #endif /* _GLIBCXX_STREAMBUF */