Info file iostream.info, produced by Makeinfo, -*- Text -*- from input file iostream.texi. START-INFO-DIR-ENTRY * iostream: (iostream). The C++ input/output facility. END-INFO-DIR-ENTRY  File: iostream.info, Node: Top, Next: Introduction, Prev: (DIR), Up: (DIR) * Menu: * Introduction:: * Using the iostream layer:: * Using the streambuf layer:: * stdio - C-style input/output:: * Streambuf internals:: Indices: * Function and Variable Index:: * Concept Index::  File: iostream.info, Node: Introduction, Next: Using the iostream layer, Prev: Top, Up: Top Introduction ************ The `iostream' library was written by Per Bothner. Various people have found bugs or come with suggestions. Hongjiu Lu has worked hard to use the library as the default stdio implementation for Linux, and has provided much stress-testing of the library. Some code was derived from parts of BSD 4.4, which is copyright University of California at Berkeley.  File: iostream.info, Node: Using the iostream layer, Next: Using the streambuf layer, Prev: Introduction, Up: Top Using the iostream layer ************************  File: iostream.info, Node: Using the streambuf layer, Next: stdio - C-style input/output, Prev: Using the iostream layer, Up: Top Using the streambuf layer ************************* * Menu: * Backing up::  File: iostream.info, Node: Backing up, Up: Using the streambuf layer Backing up ========== The GNU iostream library allows you to ask streambuf to remember the current position, and then later after you've read further be able to go back to it. Your're guaranteed to be able to backup arbitrary amounts, even on unbuffered files or multiple buffers worth, as long as you tell the library advance. This unbounded backup is very useful for scanning and parsing applications. This example shows a typical scenario: // Read either "dog", "hound", or "hounddog". // If "dog" is found, return 1. // If "hound" is found, return 2. // If "hounddog" is found, return 3. // If non of these are found, return -1. int my_scan(streambuf* sb) { streammarker fence(sb); char buffer[20]; // Try reading "hounddog": if (sb->sgetn(buffer, 8) == 8 && strncmp(buffer, "hounddog", 8) == 0) return 3; // No, no "hounddog": Backup to 'fence' ... sb->seekmark(fence); // // ... and try reading "dog": if (sb->sgetn(buffer, 3) == 3 && strncmp(buffer, "dog", 3) == 0) return 1; // No, no "dog" either: Backup to 'fence' ... sb->seekmark(fence); // // ... and try reading "hound": if (sb->sgetn(buffer, 5) == 5 && strncmp(buffer, "hound", 5) == 0) return 2; // No, no "hound" either: Backup to 'fence' and signal failure. sb->seekmark(fence); // Backup to 'fence'.. return -1; } * Constructor: streammarker::streammarker (streambuf* SBUF) Create a `streammarker' associated with SBUF that remembers the current postion of the get pointer. * Method: int streammarker::delta (streammarker& MARK2) Return the difference between the get positions corresponding to `*this' and MARK2 (which must point into the same `streambuffer' as `this'). * Method: int streammarker::delta () Return the position relative to the streambuffer's current get position. * Method: int streambuffer::seekmark (streammarker& MARK) Move the get pointer to where it (logicly) was when MARK was constructed.  File: iostream.info, Node: stdio - C-style input/output, Next: Streambuf internals, Prev: Using the streambuf layer, Up: Top stdio: C input/output ********************* Iostreams is distributed with a complete implementation of the ANSI C stdio facility. It is implemented using streambufs. The stdio package is intended as a replacement for the whatever stdio is in your C library. It can co-exist with C libraries that have alternate implementations of stdio, but there may be some problems. Since stdio works best when you build libc to contain it, and that may be inconvenient, it is not installed by default. Extensions beyond ANSI: * A stdio FILE is identical to a streambuf. Hence there is no need to worry about synchronizing C and C++ input/output - they are by definition always synchronized. * If you create a new streambuf sub-class (in C++), you can use it as a FILE from C. Thus the system is extensible using the standard streambuf protocol. * You can arbitrarily mix reading and writing, without having to seek in between. * Unbounded ungetc() buffer.  File: iostream.info, Node: Streambuf internals, Next: Function and Variable Index, Prev: stdio - C-style input/output, Up: Top Streambuf internals ******************* * Menu: * Buffer management:: * Filebuf internals::  File: iostream.info, Node: Buffer management, Next: Filebuf internals, Up: Streambuf internals Buffer management ================= Areas ----- Streambuf buffer management is fairly sophisticated (this is a nice way to say "complicated"). The standard protocol has the following "areas": * The "put area" contains characters waiting for output. * The "get area" contains characters available for reading. * The "reserve area" is available to virtual methods. Usually, the get and/or put areas are part of the reserve area. The GNU streambuf design extends this by supporting two get areas: * The "main get area" contains characters that have been read in from the character source, but not yet read by the application. * The "backup area" contains previously read data that is being saved because of a user request, or that have been "unread" (putback). The backup and the main get area are logically contiguous: That is, the first character of the main get area follows the last character of the backup area. The "current get area" is whichever one of the backup or main get areas that is currently being read from. The other of the two is the "non-current get area". Pointers -------- The following `char*' pointers define the various areas. (Note that if a pointer points to the 'end' of an area, it means that it points to the character after the area.) * Method: char* streambuffer::base () The start of the reserve area. * Method: char* streambuffer::ebuf () The end of the reserve area. * Method: char* streambuffer::pbase () The start of the put area. * Method: char* streambuffer::pptr () The current put position. If `pptr() < epptr()', then the next write will overwrite `*pptr()', and increment `pptr()'. * Method: char* streambuffer::epptr () The end of the put area. * Method: char* streambuffer::eback () The start of the current get area. * Method: char* streambuffer::gptr () The current get position. If `gptr() < egptr()', then the next read will read `*gptr()', and increment `gptr()'. * Method: char* streambuffer::egptr () The end of the current get area. * Method: char* streambuffer::Gbase () The start of the main get area. * Method: char* streambuffer::eGptr () The end of the main get area. * Method: char* streambuffer::Bbase () The start of the backup area. * Method: char* streambuffer::Bptr () The start of the used part of the backup area. The area (`Bptr()' .. `eBptr()') contains data that has been pushed back, while (`Bbase()' .. `eBptr()') contains unused space available for future putbacks. * Method: char* streambuffer::eBptr () The end of the backup area. * Method: char* streambuffer::Nbase () The start of the non-current get area (either `main_gbase' or `backup_gbase'). * Method: char* streambuffer::eNptr () The end of the non-current get area.  File: iostream.info, Node: Filebuf internals, Prev: Buffer management, Up: Streambuf internals Filebuf internals ================= The `filebuf' is used a lot, so it is importamt that it be efficient. It is also supports rather complex semantics. so let us examine its implementation. Tied read and write pointers ---------------------------- The streambuf model allows completely independent read and write pointers. However, a `filebuf' has only a single logical pointer used for both reads and writes. Since the `streambuf' protocol uses `gptr()' for reading and `pptr()' for writing, we map the logical file pointer into either `gptr()' or `pptr()' at different times. * Reading is allowed when `gptr() < egptr()', which we call get mode. * Writing is allowed when `pptr() < epptr()', which we call put mode. A `filebuf' cannot be in put get mode and put mode at the same time. We have upto two buffers: * The backeup area, defined by `Bbase()', `Bptr()', and `eBptr()'. This can be empty. * The reserve area, which also contains the main get area. For an unbuffered file, the (`shortbuf()'..`shortbuf()+1') is used, where `shortbuf()' points to a 1-byte buffer that is part of the `filebuf'. The file system's idea of the current position is `eGptr()'. Character that have been written into a buffer but not yet written out (flushed) to the file systems are those between `pbase()' and `pptr()'. The end of the valid data bytes is: `pptr() > eGptr() && pptr() < ebuf() ? pptr() : eGptr()'. If the `filebuf' is unbuffered or line buffered, the `eptr()' is `pbase()'. This forces a call to `overflow()' on each put of a character. The logical `epptr()' is `epptr() ? ebuf() : NULL'. (If the buffer is read-only, set `pbase()', `pptr()', and `epptr()' to `NULL'.)  File: iostream.info, Node: Function and Variable Index, Next: Concept Index, Prev: Streambuf internals, Up: Top Function and Variable Index,Concept Index,,Top ********************************************** * Menu: * streambuffer::Bbase: Buffer management. * streambuffer::Bptr: Buffer management. * streambuffer::Gbase: Buffer management. * streambuffer::Nbase: Buffer management. * streambuffer::base: Buffer management. * streambuffer::eBptr: Buffer management. * streambuffer::eGptr: Buffer management. * streambuffer::eNptr: Buffer management. * streambuffer::eback: Buffer management. * streambuffer::ebuf: Buffer management. * streambuffer::egptr: Buffer management. * streambuffer::epptr: Buffer management. * streambuffer::gptr: Buffer management. * streambuffer::pbase: Buffer management. * streambuffer::pptr: Buffer management. * streambuffer::seekmark: Backing up. * streammarker::delta: Backing up. * streammarker::delta: Backing up. * streammarker::streammarker: Backing up.  File: iostream.info, Node: Concept Index, Prev: Function and Variable Index, Up: Top Concept Index,,Function and Variable Index,Top ********************************************** * Menu: * backup area: Buffer management. * get area: Buffer management. * main get area: Buffer management. * put area: Buffer management. * reserve area: Buffer management.  Tag Table: Node: Top201 Node: Introduction486 Node: Using the iostream layer981 Node: Using the streambuf layer1153 Node: Backing up1368 Node: stdio - C-style input/output3599 Node: Streambuf internals4733 Node: Buffer management4962 Node: Filebuf internals7964 Node: Function and Variable Index9825 Node: Concept Index11142  End Tag Table