std_streambuf.h revision 117397
1// Stream buffer classes -*- C++ -*- 2 3// Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002, 2003 4// Free Software Foundation, Inc. 5// 6// This file is part of the GNU ISO C++ Library. This library is free 7// software; you can redistribute it and/or modify it under the 8// terms of the GNU General Public License as published by the 9// Free Software Foundation; either version 2, or (at your option) 10// any later version. 11 12// This library is distributed in the hope that it will be useful, 13// but WITHOUT ANY WARRANTY; without even the implied warranty of 14// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 15// GNU General Public License for more details. 16 17// You should have received a copy of the GNU General Public License along 18// with this library; see the file COPYING. If not, write to the Free 19// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, 20// USA. 21 22// As a special exception, you may use this file as part of a free software 23// library without restriction. Specifically, if other files instantiate 24// templates or use macros or inline functions from this file, or you compile 25// this file and link it with other files to produce an executable, this 26// file does not by itself cause the resulting executable to be covered by 27// the GNU General Public License. This exception does not however 28// invalidate any other reasons why the executable file might be covered by 29// the GNU General Public License. 30 31// 32// ISO C++ 14882: 27.5 Stream buffers 33// 34 35/** @file streambuf 36 * This is a Standard C++ Library header. You should @c #include this header 37 * in your programs, rather than any of the "st[dl]_*.h" implementation files. 38 */ 39 40#ifndef _CPP_STREAMBUF 41#define _CPP_STREAMBUF 1 42 43#pragma GCC system_header 44 45#include <bits/c++config.h> 46#include <iosfwd> 47#include <cstdio> // For SEEK_SET, SEEK_CUR, SEEK_END 48#include <bits/localefwd.h> 49#include <bits/ios_base.h> 50 51namespace std 52{ 53 /** 54 * @if maint 55 * Does stuff. 56 * @endif 57 */ 58 template<typename _CharT, typename _Traits> 59 streamsize 60 __copy_streambufs(basic_ios<_CharT, _Traits>& _ios, 61 basic_streambuf<_CharT, _Traits>* __sbin, 62 basic_streambuf<_CharT, _Traits>* __sbout); 63 64 /** 65 * @brief The actual work of input and output (interface). 66 * 67 * This is a base class. Derived stream buffers each control a 68 * pair of character sequences: one for input, and one for output. 69 * 70 * Section [27.5.1] of the standard describes the requirements and 71 * behavior of stream buffer classes. That section (three paragraphs) 72 * is reproduced here, for simplicity and accuracy. 73 * 74 * -# Stream buffers can impose various constraints on the sequences 75 * they control. Some constraints are: 76 * - The controlled input sequence can be not readable. 77 * - The controlled output sequence can be not writable. 78 * - The controlled sequences can be associated with the contents of 79 * other representations for character sequences, such as external 80 * files. 81 * - The controlled sequences can support operations @e directly to or 82 * from associated sequences. 83 * - The controlled sequences can impose limitations on how the 84 * program can read characters from a sequence, write characters to 85 * a sequence, put characters back into an input sequence, or alter 86 * the stream position. 87 * . 88 * -# Each sequence is characterized by three pointers which, if non-null, 89 * all point into the same @c charT array object. The array object 90 * represents, at any moment, a (sub)sequence of characters from the 91 * sequence. Operations performed on a sequence alter the values 92 * stored in these pointers, perform reads and writes directly to or 93 * from associated sequences, and alter "the stream position" and 94 * conversion state as needed to maintain this subsequence relationship. 95 * The three pointers are: 96 * - the <em>beginning pointer</em>, or lowest element address in the 97 * array (called @e xbeg here); 98 * - the <em>next pointer</em>, or next element address that is a 99 * current candidate for reading or writing (called @e xnext here); 100 * - the <em>end pointer</em>, or first element address beyond the 101 * end of the array (called @e xend here). 102 * . 103 * -# The following semantic constraints shall always apply for any set 104 * of three pointers for a sequence, using the pointer names given 105 * immediately above: 106 * - If @e xnext is not a null pointer, then @e xbeg and @e xend shall 107 * also be non-null pointers into the same @c charT array, as 108 * described above; otherwise, @e xbeg and @e xend shall also be null. 109 * - If @e xnext is not a null pointer and @e xnext < @e xend for an 110 * output sequence, then a <em>write position</em> is available. 111 * In this case, @e *xnext shall be assignable as the next element 112 * to write (to put, or to store a character value, into the sequence). 113 * - If @e xnext is not a null pointer and @e xbeg < @e xnext for an 114 * input sequence, then a <em>putback position</em> is available. 115 * In this case, @e xnext[-1] shall have a defined value and is the 116 * next (preceding) element to store a character that is put back 117 * into the input sequence. 118 * - If @e xnext is not a null pointer and @e xnext< @e xend for an 119 * input sequence, then a <em>read position</em> is available. 120 * In this case, @e *xnext shall have a defined value and is the 121 * next element to read (to get, or to obtain a character value, 122 * from the sequence). 123 */ 124 template<typename _CharT, typename _Traits> 125 class basic_streambuf 126 { 127 public: 128 //@{ 129 /** 130 * These are standard types. They permit a standardized way of 131 * referring to names of (or names dependant on) the template 132 * parameters, which are specific to the implementation. 133 */ 134 typedef _CharT char_type; 135 typedef _Traits traits_type; 136 typedef typename traits_type::int_type int_type; 137 typedef typename traits_type::pos_type pos_type; 138 typedef typename traits_type::off_type off_type; 139 //@} 140 141 //@{ 142 /** 143 * @if maint 144 * These are non-standard types. 145 * @endif 146 */ 147 typedef ctype<char_type> __ctype_type; 148 typedef basic_streambuf<char_type, traits_type> __streambuf_type; 149 typedef typename traits_type::state_type __state_type; 150 //@} 151 152 friend class basic_ios<char_type, traits_type>; 153 friend class basic_istream<char_type, traits_type>; 154 friend class basic_ostream<char_type, traits_type>; 155 friend class istreambuf_iterator<char_type, traits_type>; 156 friend class ostreambuf_iterator<char_type, traits_type>; 157 158 friend streamsize 159 __copy_streambufs<>(basic_ios<char_type, traits_type>& __ios, 160 __streambuf_type* __sbin,__streambuf_type* __sbout); 161 162 protected: 163 /** 164 * @if maint 165 * Pointer to the beginning of internally-allocated space. Filebuf 166 * manually allocates/deallocates this, whereas stringstreams attempt 167 * to use the built-in intelligence of the string class. If you are 168 * managing memory, set this. If not, leave it NULL. 169 * @endif 170 */ 171 char_type* _M_buf; 172 173 /** 174 * @if maint 175 * Actual size of allocated internal buffer, in bytes. 176 * @endif 177 */ 178 size_t _M_buf_size; 179 180 /** 181 * @if maint 182 * Optimal or preferred size of internal buffer, in bytes. 183 * @endif 184 */ 185 size_t _M_buf_size_opt; 186 187 /** 188 * @if maint 189 * True iff _M_in_* and _M_out_* buffers should always point to 190 * the same place. True for fstreams, false for sstreams. 191 * @endif 192 */ 193 bool _M_buf_unified; 194 195 //@{ 196 /** 197 * @if maint 198 * This is based on _IO_FILE, just reordered to be more consistent, 199 * and is intended to be the most minimal abstraction for an 200 * internal buffer. 201 * - get == input == read 202 * - put == output == write 203 * @endif 204 */ 205 char_type* _M_in_beg; // Start of get area. 206 char_type* _M_in_cur; // Current read area. 207 char_type* _M_in_end; // End of get area. 208 char_type* _M_out_beg; // Start of put area. 209 char_type* _M_out_cur; // Current put area. 210 char_type* _M_out_end; // End of put area. 211 //@} 212 213 /** 214 * @if maint 215 * Place to stash in || out || in | out settings for current streambuf. 216 * @endif 217 */ 218 ios_base::openmode _M_mode; 219 220 /** 221 * @if maint 222 * Current locale setting. 223 * @endif 224 */ 225 locale _M_buf_locale; 226 227 /** 228 * @if maint 229 * True iff locale is initialized. 230 * @endif 231 */ 232 bool _M_buf_locale_init; 233 234 //@{ 235 /** 236 * @if maint 237 * Necessary bits for putback buffer management. Only used in 238 * the basic_filebuf class, as necessary for the standard 239 * requirements. The only basic_streambuf member function that 240 * needs access to these data members is in_avail... 241 * 242 * @note pbacks of over one character are not currently supported. 243 * @endif 244 */ 245 static const size_t _S_pback_size = 1; 246 char_type _M_pback[_S_pback_size]; 247 char_type* _M_pback_cur_save; 248 char_type* _M_pback_end_save; 249 bool _M_pback_init; 250 //@} 251 252 /** 253 * @if maint 254 * Yet unused. 255 * @endif 256 */ 257 fpos<__state_type> _M_pos; 258 259 // Initializes pback buffers, and moves normal buffers to safety. 260 // Assumptions: 261 // _M_in_cur has already been moved back 262 void 263 _M_pback_create() 264 { 265 if (!_M_pback_init) 266 { 267 size_t __dist = _M_in_end - _M_in_cur; 268 size_t __len = min(_S_pback_size, __dist); 269 traits_type::copy(_M_pback, _M_in_cur, __len); 270 _M_pback_cur_save = _M_in_cur; 271 _M_pback_end_save = _M_in_end; 272 this->setg(_M_pback, _M_pback, _M_pback + __len); 273 _M_pback_init = true; 274 } 275 } 276 277 // Deactivates pback buffer contents, and restores normal buffer. 278 // Assumptions: 279 // The pback buffer has only moved forward. 280 void 281 _M_pback_destroy() throw() 282 { 283 if (_M_pback_init) 284 { 285 // Length _M_in_cur moved in the pback buffer. 286 size_t __off_cur = _M_in_cur - _M_pback; 287 288 // For in | out buffers, the end can be pushed back... 289 size_t __off_end = 0; 290 size_t __pback_len = _M_in_end - _M_pback; 291 size_t __save_len = _M_pback_end_save - _M_buf; 292 if (__pback_len > __save_len) 293 __off_end = __pback_len - __save_len; 294 295 this->setg(_M_buf, _M_pback_cur_save + __off_cur, 296 _M_pback_end_save + __off_end); 297 _M_pback_cur_save = NULL; 298 _M_pback_end_save = NULL; 299 _M_pback_init = false; 300 } 301 } 302 303 // Correctly sets the _M_in_cur pointer, and bumps the 304 // _M_out_cur pointer as well if necessary. 305 void 306 _M_in_cur_move(off_type __n) // argument needs to be +- 307 { 308 bool __testout = _M_out_cur; 309 _M_in_cur += __n; 310 if (__testout && _M_buf_unified) 311 _M_out_cur += __n; 312 } 313 314 // Correctly sets the _M_out_cur pointer, and bumps the 315 // appropriate _M_*_end pointers as well. Necessary for the 316 // un-tied stringbufs, in in|out mode. 317 // Invariant: 318 // __n + _M_out_[cur, end] <= _M_buf + _M_buf_size 319 // Assuming all _M_*_[beg, cur, end] pointers are operating on 320 // the same range: 321 // _M_buf <= _M_*_ <= _M_buf + _M_buf_size 322 void 323 _M_out_cur_move(off_type __n) // argument needs to be +- 324 { 325 bool __testin = _M_in_cur; 326 327 _M_out_cur += __n; 328 if (__testin && _M_buf_unified) 329 _M_in_cur += __n; 330 if (_M_out_cur > _M_out_end) 331 { 332 _M_out_end = _M_out_cur; 333 // NB: in | out buffers drag the _M_in_end pointer along... 334 if (__testin) 335 _M_in_end += __n; 336 } 337 } 338 339 // Return the size of the output buffer. This depends on the 340 // buffer in use: allocated buffers have a stored size in 341 // _M_buf_size and setbuf() buffers don't. 342 off_type 343 _M_out_buf_size() 344 { 345 off_type __ret = 0; 346 if (_M_out_cur) 347 { 348 // Using allocated buffer. 349 if (_M_out_beg == _M_buf) 350 __ret = _M_out_beg + _M_buf_size - _M_out_cur; 351 // Using non-allocated buffer. 352 else 353 __ret = _M_out_end - _M_out_cur; 354 } 355 return __ret; 356 } 357 358 public: 359 /// Destructor deallocates no buffer space. 360 virtual 361 ~basic_streambuf() 362 { 363 _M_buf_unified = false; 364 _M_buf_size = 0; 365 _M_buf_size_opt = 0; 366 _M_mode = ios_base::openmode(0); 367 } 368 369 // [27.5.2.2.1] locales 370 /** 371 * @brief Entry point for imbue(). 372 * @param loc The new locale. 373 * @return The previous locale. 374 * 375 * Calls the derived imbue(loc). 376 */ 377 locale 378 pubimbue(const locale &__loc) 379 { 380 locale __tmp(this->getloc()); 381 this->imbue(__loc); 382 return __tmp; 383 } 384 385 /** 386 * @brief Locale access. 387 * @return The current locale in effect. 388 * 389 * If pubimbue(loc) has been called, then the most recent @c loc 390 * is returned. Otherwise the global locale in effect at the time 391 * of construction is returned. 392 */ 393 locale 394 getloc() const 395 { return _M_buf_locale; } 396 397 // [27.5.2.2.2] buffer management and positioning 398 //@{ 399 /** 400 * @brief Entry points for derived buffer functions. 401 * 402 * The public versions of @c pubfoo dispatch to the protected 403 * derived @c foo member functions, passing the arguments (if any) 404 * and returning the result unchanged. 405 */ 406 __streambuf_type* 407 pubsetbuf(char_type* __s, streamsize __n) 408 { return this->setbuf(__s, __n); } 409 410 pos_type 411 pubseekoff(off_type __off, ios_base::seekdir __way, 412 ios_base::openmode __mode = ios_base::in | ios_base::out) 413 { return this->seekoff(__off, __way, __mode); } 414 415 pos_type 416 pubseekpos(pos_type __sp, 417 ios_base::openmode __mode = ios_base::in | ios_base::out) 418 { return this->seekpos(__sp, __mode); } 419 420 int 421 pubsync() { return this->sync(); } 422 //@} 423 424 // [27.5.2.2.3] get area 425 /** 426 * @brief Looking ahead into the stream. 427 * @return The number of characters available. 428 * 429 * If a read position is available, returns the number of characters 430 * available for reading before the buffer must be refilled. 431 * Otherwise returns the derived @c showmanyc(). 432 */ 433 streamsize 434 in_avail() 435 { 436 streamsize __ret; 437 if (_M_in_cur && _M_in_cur < _M_in_end) 438 { 439 if (_M_pback_init) 440 { 441 size_t __save_len = _M_pback_end_save - _M_pback_cur_save; 442 size_t __pback_len = _M_in_cur - _M_pback; 443 __ret = __save_len - __pback_len; 444 } 445 else 446 __ret = this->egptr() - this->gptr(); 447 } 448 else 449 __ret = this->showmanyc(); 450 return __ret; 451 } 452 453 /** 454 * @brief Getting the next character. 455 * @return The next character, or eof. 456 * 457 * Calls @c sbumpc(), and if that function returns 458 * @c traits::eof(), so does this function. Otherwise, @c sgetc(). 459 */ 460 int_type 461 snextc() 462 { 463 int_type __eof = traits_type::eof(); 464 return (traits_type::eq_int_type(this->sbumpc(), __eof) 465 ? __eof : this->sgetc()); 466 } 467 468 /** 469 * @brief Getting the next character. 470 * @return The next character, or eof. 471 * 472 * If the input read position is available, returns that character 473 * and increments the read pointer, otherwise calls and returns 474 * @c uflow(). 475 */ 476 int_type 477 sbumpc(); 478 479 /** 480 * @brief Getting the next character. 481 * @return The next character, or eof. 482 * 483 * If the input read position is available, returns that character, 484 * otherwise calls and returns @c underflow(). Does not move the 485 * read position after fetching the character. 486 */ 487 int_type 488 sgetc() 489 { 490 int_type __ret; 491 if (_M_in_cur && _M_in_cur < _M_in_end) 492 __ret = traits_type::to_int_type(*(this->gptr())); 493 else 494 __ret = this->underflow(); 495 return __ret; 496 } 497 498 /** 499 * @brief Entry point for xsgetn. 500 * @param s A buffer area. 501 * @param n A count. 502 * 503 * Returns xsgetn(s,n). The effect is to fill @a s[0] through 504 * @a s[n-1] with characters from the input sequence, if possible. 505 */ 506 streamsize 507 sgetn(char_type* __s, streamsize __n) 508 { return this->xsgetn(__s, __n); } 509 510 // [27.5.2.2.4] putback 511 /** 512 * @brief Pushing characters back into the input stream. 513 * @param c The character to push back. 514 * @return The previous character, if possible. 515 * 516 * Similar to sungetc(), but @a c is pushed onto the stream instead 517 * of "the previous character". If successful, the next character 518 * fetched from the input stream will be @a c. 519 */ 520 int_type 521 sputbackc(char_type __c); 522 523 /** 524 * @brief Moving backwards in the input stream. 525 * @return The previous character, if possible. 526 * 527 * If a putback position is available, this function decrements the 528 * input pointer and returns that character. Otherwise, calls and 529 * returns pbackfail(). The effect is to "unget" the last character 530 * "gotten". 531 */ 532 int_type 533 sungetc(); 534 535 // [27.5.2.2.5] put area 536 /** 537 * @brief Entry point for all single-character output functions. 538 * @param c A character to output. 539 * @return @a c, if possible. 540 * 541 * One of two public output functions. 542 * 543 * If a write position is available for the output sequence (i.e., 544 * the buffer is not full), stores @a c in that position, increments 545 * the position, and returns @c traits::to_int_type(c). If a write 546 * position is not available, returns @c overflow(c). 547 */ 548 int_type 549 sputc(char_type __c); 550 551 /** 552 * @brief Entry point for all single-character output functions. 553 * @param s A buffer read area. 554 * @param n A count. 555 * 556 * One of two public output functions. 557 * 558 * 559 * Returns xsputn(s,n). The effect is to write @a s[0] through 560 * @a s[n-1] to the output sequence, if possible. 561 */ 562 streamsize 563 sputn(const char_type* __s, streamsize __n) 564 { return this->xsputn(__s, __n); } 565 566 protected: 567 /** 568 * @brief Base constructor. 569 * 570 * Only called from derived constructors, and sets up all the 571 * buffer data to zero, including the pointers described in the 572 * basic_streambuf class description. Note that, as a result, 573 * - the class starts with no read nor write positions available, 574 * - this is not an error 575 */ 576 basic_streambuf() 577 : _M_buf(NULL), _M_buf_size(0), _M_buf_size_opt(BUFSIZ), 578 _M_buf_unified(false), _M_in_beg(0), _M_in_cur(0), _M_in_end(0), 579 _M_out_beg(0), _M_out_cur(0), _M_out_end(0), 580 _M_mode(ios_base::openmode(0)), _M_buf_locale(locale()), 581 _M_pback_cur_save(0), _M_pback_end_save(0), 582 _M_pback_init(false) 583 { } 584 585 // [27.5.2.3.1] get area access 586 //@{ 587 /** 588 * @brief Access to the get area. 589 * 590 * These functions are only available to other protected functions, 591 * including derived classes. 592 * 593 * - eback() returns the beginning pointer for the input sequence 594 * - gptr() returns the next pointer for the input sequence 595 * - egptr() returns the end pointer for the input sequence 596 */ 597 char_type* 598 eback() const { return _M_in_beg; } 599 600 char_type* 601 gptr() const { return _M_in_cur; } 602 603 char_type* 604 egptr() const { return _M_in_end; } 605 //@} 606 607 /** 608 * @brief Moving the read position. 609 * @param n The delta by which to move. 610 * 611 * This just advances the read position without returning any data. 612 */ 613 void 614 gbump(int __n) { _M_in_cur += __n; } 615 616 /** 617 * @brief Setting the three read area pointers. 618 * @param gbeg A pointer. 619 * @param gnext A pointer. 620 * @param gend A pointer. 621 * @post @a gbeg == @c eback(), @a gnext == @c gptr(), and 622 * @a gend == @c egptr() 623 */ 624 void 625 setg(char_type* __gbeg, char_type* __gnext, char_type* __gend) 626 { 627 _M_in_beg = __gbeg; 628 _M_in_cur = __gnext; 629 _M_in_end = __gend; 630 if (!(_M_mode & ios_base::in) && __gbeg && __gnext && __gend) 631 _M_mode = _M_mode | ios_base::in; 632 } 633 634 // [27.5.2.3.2] put area access 635 //@{ 636 /** 637 * @brief Access to the put area. 638 * 639 * These functions are only available to other protected functions, 640 * including derived classes. 641 * 642 * - pbase() returns the beginning pointer for the output sequence 643 * - pptr() returns the next pointer for the output sequence 644 * - epptr() returns the end pointer for the output sequence 645 */ 646 char_type* 647 pbase() const { return _M_out_beg; } 648 649 char_type* 650 pptr() const { return _M_out_cur; } 651 652 char_type* 653 epptr() const { return _M_out_end; } 654 //@} 655 656 /** 657 * @brief Moving the write position. 658 * @param n The delta by which to move. 659 * 660 * This just advances the write position without returning any data. 661 */ 662 void 663 pbump(int __n) { _M_out_cur += __n; } 664 665 /** 666 * @brief Setting the three write area pointers. 667 * @param pbeg A pointer. 668 * @param pend A pointer. 669 * @post @a pbeg == @c pbase(), @a pbeg == @c pptr(), and 670 * @a pend == @c epptr() 671 */ 672 void 673 setp(char_type* __pbeg, char_type* __pend) 674 { 675 _M_out_beg = _M_out_cur = __pbeg; 676 _M_out_end = __pend; 677 if (!(_M_mode & ios_base::out) && __pbeg && __pend) 678 _M_mode = _M_mode | ios_base::out; 679 } 680 681 // [27.5.2.4] virtual functions 682 // [27.5.2.4.1] locales 683 /** 684 * @brief Changes translations. 685 * @param loc A new locale. 686 * 687 * Translations done during I/O which depend on the current locale 688 * are changed by this call. The standard adds, "Between invocations 689 * of this function a class derived from streambuf can safely cache 690 * results of calls to locale functions and to members of facets 691 * so obtained." This function simply stores the new locale for use 692 * by derived classes. 693 */ 694 virtual void 695 imbue(const locale& __loc) 696 { 697 if (_M_buf_locale != __loc) 698 _M_buf_locale = __loc; 699 } 700 701 // [27.5.2.4.2] buffer management and positioning 702 /** 703 * @brief Maniuplates the buffer. 704 * 705 * Each derived class provides its own appropriate behavior. See 706 * the next-to-last paragraph of 707 * http://gcc.gnu.org/onlinedocs/libstdc++/27_io/howto.html#2 for 708 * more on this function. 709 * 710 * @note Base class version does nothing, returns @c this. 711 */ 712 virtual basic_streambuf<char_type,_Traits>* 713 setbuf(char_type*, streamsize) 714 { return this; } 715 716 /** 717 * @brief Alters the stream positions. 718 * 719 * Each derived class provides its own appropriate behavior. 720 * @note Base class version does nothing, returns a @c pos_type 721 * that represents an invalid stream position. 722 */ 723 virtual pos_type 724 seekoff(off_type, ios_base::seekdir, 725 ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out) 726 { return pos_type(off_type(-1)); } 727 728 /** 729 * @brief Alters the stream positions. 730 * 731 * Each derived class provides its own appropriate behavior. 732 * @note Base class version does nothing, returns a @c pos_type 733 * that represents an invalid stream position. 734 */ 735 virtual pos_type 736 seekpos(pos_type, 737 ios_base::openmode /*__mode*/ = ios_base::in | ios_base::out) 738 { return pos_type(off_type(-1)); } 739 740 /** 741 * @brief Synchronizes the buffer arrays with the controlled sequences. 742 * @return -1 on failure. 743 * 744 * Each derived class provides its own appropriate behavior, 745 * including the definition of "failure". 746 * @note Base class version does nothing, returns zero. 747 */ 748 virtual int 749 sync() { return 0; } 750 751 // [27.5.2.4.3] get area 752 /** 753 * @brief Investigating the data available. 754 * @return An estimate of the number of characters available in the 755 * input sequence, or -1. 756 * 757 * "If it returns a positive value, then successive calls to 758 * @c underflow() will not return @c traits::eof() until at least that 759 * number of characters have been supplied. If @c showmanyc() 760 * returns -1, then calls to @c underflow() or @c uflow() will fail." 761 * [27.5.2.4.3]/1 762 * 763 * @note Base class version does nothing, returns zero. 764 * @note The standard adds that "the intention is not only that the 765 * calls [to underflow or uflow] will not return @c eof() but 766 * that they will return "immediately". 767 * @note The standard adds that "the morphemes of @c showmanyc are 768 * "es-how-many-see", not "show-manic". 769 */ 770 virtual streamsize 771 showmanyc() { return 0; } 772 773 /** 774 * @brief Multiple character extraction. 775 * @param s A buffer area. 776 * @param n Maximum number of characters to assign. 777 * @return The number of characters assigned. 778 * 779 * Fills @a s[0] through @a s[n-1] with characters from the input 780 * sequence, as if by @c sbumpc(). Stops when either @a n characters 781 * have been copied, or when @c traits::eof() would be copied. 782 * 783 * It is expected that derived classes provide a more efficient 784 * implementation by overriding this definition. 785 */ 786 virtual streamsize 787 xsgetn(char_type* __s, streamsize __n); 788 789 /** 790 * @brief Fetches more data from the controlled sequence. 791 * @return The first character from the <em>pending sequence</em>. 792 * 793 * Informally, this function is called when the input buffer is 794 * exhausted (or does not exist, as buffering need not actually be 795 * done). If a buffer exists, it is "refilled". In either case, the 796 * next available character is returned, or @c traits::eof() to 797 * indicate a null pending sequence. 798 * 799 * For a formal definiton of the pending sequence, see a good text 800 * such as Langer & Kreft, or [27.5.2.4.3]/7-14. 801 * 802 * A functioning input streambuf can be created by overriding only 803 * this function (no buffer area will be used). For an example, see 804 * http://gcc.gnu.org/onlinedocs/libstdc++/27_io/howto.html#6 805 * 806 * @note Base class version does nothing, returns eof(). 807 */ 808 virtual int_type 809 underflow() 810 { return traits_type::eof(); } 811 812 /** 813 * @brief Fetches more data from the controlled sequence. 814 * @return The first character from the <em>pending sequence</em>. 815 * 816 * Informally, this function does the same thing as @c underflow(), 817 * and in fact is required to call that function. It also returns 818 * the new character, like @c underflow() does. However, this 819 * function also moves the read position forward by one. 820 */ 821 virtual int_type 822 uflow() 823 { 824 int_type __ret = traits_type::eof(); 825 bool __testeof = traits_type::eq_int_type(this->underflow(), __ret); 826 bool __testpending = _M_in_cur && _M_in_cur < _M_in_end; 827 if (!__testeof && __testpending) 828 { 829 __ret = traits_type::to_int_type(*_M_in_cur); 830 ++_M_in_cur; 831 if (_M_buf_unified && _M_mode & ios_base::out) 832 ++_M_out_cur; 833 } 834 return __ret; 835 } 836 837 // [27.5.2.4.4] putback 838 /** 839 * @brief Tries to back up the input sequence. 840 * @param c The character to be inserted back into the sequence. 841 * @return eof() on failure, "some other value" on success 842 * @post The constraints of @c gptr(), @c eback(), and @c pptr() 843 * are the same as for @c underflow(). 844 * 845 * @note Base class version does nothing, returns eof(). 846 */ 847 virtual int_type 848 pbackfail(int_type /* __c */ = traits_type::eof()) 849 { return traits_type::eof(); } 850 851 // Put area: 852 /** 853 * @brief Multiple character insertion. 854 * @param s A buffer area. 855 * @param n Maximum number of characters to write. 856 * @return The number of characters written. 857 * 858 * Writes @a s[0] through @a s[n-1] to the output sequence, as if 859 * by @c sputc(). Stops when either @a n characters have been 860 * copied, or when @c sputc() would return @c traits::eof(). 861 * 862 * It is expected that derived classes provide a more efficient 863 * implementation by overriding this definition. 864 */ 865 virtual streamsize 866 xsputn(const char_type* __s, streamsize __n); 867 868 /** 869 * @brief Consumes data from the buffer; writes to the 870 * controlled sequence. 871 * @param c An additional character to consume. 872 * @return eof() to indicate failure, something else (usually 873 * @a c, or not_eof()) 874 * 875 * Informally, this function is called when the output buffer is full 876 * (or does not exist, as buffering need not actually be done). If a 877 * buffer exists, it is "consumed", with "some effect" on the 878 * controlled sequence. (Typically, the buffer is written out to the 879 * sequence verbatim.) In either case, the character @a c is also 880 * written out, if @a c is not @c eof(). 881 * 882 * For a formal definiton of this function, see a good text 883 * such as Langer & Kreft, or [27.5.2.4.5]/3-7. 884 * 885 * A functioning output streambuf can be created by overriding only 886 * this function (no buffer area will be used). 887 * 888 * @note Base class version does nothing, returns eof(). 889 */ 890 virtual int_type 891 overflow(int_type /* __c */ = traits_type::eof()) 892 { return traits_type::eof(); } 893 894#ifdef _GLIBCPP_DEPRECATED 895 // Annex D.6 896 public: 897 /** 898 * @brief Tosses a character. 899 * 900 * Advances the read pointer, ignoring the character that would have 901 * been read. 902 * 903 * See http://gcc.gnu.org/ml/libstdc++/2002-05/msg00168.html 904 * 905 * @note This function has been deprecated by the standard. You 906 * must define @c _GLIBCPP_DEPRECATED to make this visible; see 907 * c++config.h. 908 */ 909 void 910 stossc() 911 { 912 if (_M_in_cur < _M_in_end) 913 ++_M_in_cur; 914 else 915 this->uflow(); 916 } 917#endif 918 919#ifdef _GLIBCPP_RESOLVE_LIB_DEFECTS 920 // Side effect of DR 50. 921 private: 922 basic_streambuf(const __streambuf_type&) { }; 923 924 __streambuf_type& 925 operator=(const __streambuf_type&) { return *this; }; 926#endif 927 }; 928} // namespace std 929 930#ifdef _GLIBCPP_NO_TEMPLATE_EXPORT 931# define export 932#endif 933#ifdef _GLIBCPP_FULLY_COMPLIANT_HEADERS 934#include <bits/streambuf.tcc> 935#endif 936 937#endif 938