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diff --git a/libio/iostream.texi b/libio/iostream.texi new file mode 100644 index 00000000000..54ccced6e71 --- /dev/null +++ b/libio/iostream.texi @@ -0,0 +1,1971 @@ +\input texinfo @c -*-Texinfo-*- +@c Copyright (c) 1993 Free Software Foundation, Inc. + +@c %**start of header +@setfilename iostream.info +@settitle The GNU C++ Iostream Library +@setchapternewpage odd +@c %**end of header + +@ifinfo +@format +START-INFO-DIR-ENTRY +* iostream: (iostream). The C++ input/output facility. +END-INFO-DIR-ENTRY +@end format + +This file describes libio, the GNU library for C++ iostreams and C stdio. + +libio includes software developed by the University of California, +Berkeley. + +Copyright (C) 1993 Free Software Foundation, Inc. + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +@ignore +Permission is granted to process this file through TeX and print the +results, provided the printed document carries copying permission +notice identical to this one except for the removal of this paragraph +(this paragraph not being relevant to the printed manual). + +@end ignore +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that the +entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@end ifinfo + +@finalout +@syncodeindex fn cp +@syncodeindex vr cp + +@titlepage +@title The GNU C++ Iostream Library +@subtitle Reference Manual for @code{libio} Version 0.64 +@sp 3 +@author Per Bothner @hfill @code{bothner@@cygnus.com} +@author Cygnus Support @hfill @code{doc@@cygnus.com} +@page + +@vskip 0pt plus 1filll +Copyright @copyright{} 1993 Free Software Foundation, Inc. + +@code{libio} includes software developed by the University of +California, Berkeley. + +@code{libio} uses floating-point software written by David M. Gay, which +includes the following notice: + +@quotation +The author of this software is David M. Gay. + +Copyright (c) 1991 by AT&T. + +Permission to use, copy, modify, and distribute this software for any +purpose without fee is hereby granted, provided that this entire notice +is included in all copies of any software which is or includes a copy +or modification of this software and in all copies of the supporting +documentation for such software. + +THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED +WARRANTY. IN PARTICULAR, NEITHER THE AUTHOR NOR AT&T MAKES ANY +REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY +OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE. +@end quotation + +Permission is granted to make and distribute verbatim copies of +this manual provided the copyright notice and this permission notice +are preserved on all copies. + +Permission is granted to copy and distribute modified versions of this +manual under the conditions for verbatim copying, provided also that the +entire resulting derived work is distributed under the terms of a +permission notice identical to this one. + +Permission is granted to copy and distribute translations of this manual +into another language, under the above conditions for modified versions. +@end titlepage + +@ifinfo +@node Top +@top The GNU C++ Iostream Library + +This file provides reference information on the GNU C++ iostream library +(@code{libio}), version 0.64. + +@menu +* Introduction:: +* Operators:: Operators and default streams. +* Streams:: Stream classes. +* Files and Strings:: Classes for files and strings. +* Streambuf:: Using the streambuf layer. +* Stdio:: C input and output. +* Index:: +@end menu +@end ifinfo + +@node Introduction +@chapter Introduction + +The iostream classes implement most of the features of AT&T version 2.0 +iostream library classes, and most of the features of the ANSI X3J16 +library draft (which is based on the AT&T design). + +This manual is meant as a reference; for tutorial material on iostreams, +see the corresponding section of any recent popular introduction to C++. + +@menu +* Copying:: Special GNU licensing terms for libio. +* Acknowledgements:: Contributors to GNU iostream. +@end menu + +@node Copying +@section Licensing terms for @code{libio} + +Since the @code{iostream} classes are so fundamental to standard C++, +the Free Software Foundation has agreed to a special exception to its +standard license, when you link programs with @code{libio.a}: + +@quotation +As a special exception, if you link this library with files +compiled with a GNU compiler to produce an executable, this does not cause +the resulting executable to be covered by the GNU General Public License. +This exception does not however invalidate any other reasons why +the executable file might be covered by the GNU General Public License. +@end quotation + +The code is under the @sc{gnu} General Public License (version 2) for +all other purposes than linking with this library; that means that you +can modify and redistribute the code as usual, but remember that if you +do, your modifications, and anything you link with the modified code, +must be available to others on the same terms. + +These functions are also available as part of the @code{libg++} +library; if you link with that library instead of @code{libio}, the +@sc{gnu} Library General Public License applies. + +@node Acknowledgements +@section Acknowledgements + +Per Bothner wrote most of the @code{iostream} library, but some portions +have their origins elsewhere in the free software community. Heinz +Seidl wrote the IO manipulators. The floating-point conversion software +is by David M. Gay of AT&T. Some code was derived from parts of BSD +4.4, which was written at the University of California, Berkeley. + +The iostream classes are found in the @code{libio} library. An early +version was originally distributed in @code{libg++}, and they are still +included there as well, for convenience if you need other @code{libg++} +classes. Doug Lea was the original author of @code{libg++}, and some of +the file-management code still in @code{libio} is his. + +Various people found bugs or offered suggestions. Hongjiu Lu worked +hard to use the library as the default stdio implementation for Linux, +and has provided much stress-testing of the library. + +@node Operators +@chapter Operators and Default Streams + +The @sc{gnu} iostream library, @file{libio}, implements the standard +input and output facilities for C++. These facilities are roughly +analogous (in their purpose and ubiquity, at least) with those defined +by the C @file{stdio} functions. + +Although these definitions come from a library, rather than being part +of the ``core language'', they are sufficiently central to be specified +in the latest working papers for C++. + +You can use two operators defined in this library for basic input and +output operations. They are familiar from any C++ introductory +textbook: @code{<<} for output, and @code{>>} for input. (Think of data +flowing in the direction of the ``arrows''.) + +These operators are often used in conjunction with three streams that +are open by default: + +@deftypevar ostream cout +The standard output stream, analogous to the C @code{stdout}. +@end deftypevar + +@deftypevar istream cin +The standard input stream, analogous to the C @code{stdin}. +@end deftypevar + +@deftypevar ostream cerr +An alternative output stream for errors, analogous to the C +@code{stderr}. +@end deftypevar + +@noindent +For example, this bare-bones C++ version of the traditional ``hello'' +program uses @code{<<} and @code{cout}: + +@example +#include <iostream.h> + +int main(int argc, char **argv) +@{ + cout << "Well, hi there.\n"; + return 0; +@} +@end example + +Casual use of these operators may be seductive, but---other than in +writing throwaway code for your own use---it is not necessarily simpler +than managing input and output in any other language. For example, +robust code should check the state of the input and output streams +between operations (for example, using the method @code{good}). +@xref{States,,Checking the state of a stream}. You may also need to +adjust maximum input or output field widths, using manipulators like +@code{setw} or @code{setprecision}. + +@defop Operator ostream << +Write output to an open output stream of class @code{ostream}. +Defined by this library on any @var{object} of a C++ primitive type, and +on other classes of the library. You can overload the definition for any +of your own applications' classes. + +Returns a reference to the implied argument @code{*this} (the open stream it +writes on), permitting statements like +@example +cout << "The value of i is " << i << "\n"; +@end example +@end defop + +@defop Operator istream >> +Read input from an open input stream of class @code{istream}. Defined +by this library on primitive numeric, pointer, and string types; you can +extend the definition for any of your own applications' classes. + +Returns a reference to the implied argument @code{*this} (the open stream +it reads), permitting multiple inputs in one statement. +@end defop + +@node Streams +@chapter Stream Classes + +The previous chapter referred in passing to the classes @code{ostream} +and @code{istream}, for output and input respectively. These classes +share certain properties, captured in their base class @code{ios}. + +@menu +* Ios:: Shared properties. +* Ostream:: Managing output streams. +* Istream:: Managing input streams. +* Iostream:: Input and output together. +@end menu + +@node Ios +@section Shared properties: class @code{ios} + +The base class @code{ios} provides methods to test and manage the state +of input or output streams. + +@code{ios} delegates the job of actually reading and writing bytes to +the abstract class @code{streambuf}, which is designed to provide +buffered streams (compatible with C, in the @sc{gnu} implementation). +@xref{Streambuf,,Using the @code{streambuf} layer}, for information on +the facilities available at the @code{streambuf} level. + +@deftypefn Constructor {} ios::ios ([streambuf* @var{sb} @w{[, ostream*} @var{tie}]) +The @code{ios} constructor by default initializes a new @code{ios}, and +if you supply a @code{streambuf} @var{sb} to associate with it, sets the +state @code{good} in the new @code{ios} object. It also sets the +default properties of the new object. + +@ignore +@c FIXME--future: this (a) doesn't work, (b) is controversial at ANSI +An @code{ios} without a @code{streambuf} has the state @code{bad} until +you supply a @code{streambuf}; you can do that by assigning a new value +to the @code{ios} with @samp{=}. +@end ignore + +You can also supply an optional second argument @var{tie} to the +constructor: if present, it is an initial value for @code{ios::tie}, to +associate the new @code{ios} object with another stream. +@end deftypefn + +@deftypefn Destructor {} ios::~ios () +The @code{ios} destructor is virtual, permitting application-specific +behavior when a stream is closed---typically, the destructor frees any +storage associated with the stream and releases any other associated +objects. +@end deftypefn + +@c FIXME-future: Is @deftypefn really the best way of displaying these? + +@c FIXME-future: Undocumented: ios::_throw_failure, ios::exceptions; things +@c controlled by _STREAM_COMPAT; ios::Init; ios::_IO_fix_vtable. + +@menu +* States:: Checking the state of a stream. +* Format Control:: Choices in formatting. +* Manipulators:: Convenient ways of changing stream properties. +* Extending:: Extended data fields. +* Synchronization:: Synchronizing related streams. +* Streambuf from Ios:: Reaching the underlying streambuf. +@end menu + +@node States +@subsection Checking the state of a stream + +Use this collection of methods to test for (or signal) errors and other +exceptional conditions of streams: + +@deftypefn Method {ios::operator void*} () const +You can do a quick check on the state of the most recent operation on a +stream by examining a pointer to the stream itself. The pointer is +arbitrary except for its truth value; it is true if no failures have +occurred (@code{ios::fail} is not true). For example, you might ask for +input on @code{cin} only if all prior output operations succeeded: + +@example +if (cout) +@{ + // Everything OK so far + cin >> new_value; + @dots{} +@} +@end example +@end deftypefn + +@deftypefn Method {ios::operator !} () const +In case it is more convenient to check whether something has failed, the +operator @code{!} returns true if @code{ios::fail} is true (an operation +has failed). For example, +you might issue an error message if input failed: + +@example +if (!cin) +@{ + // Oops + cerr << "Eh?\n"; +@} +@end example +@end deftypefn + +@deftypefn Method iostate ios::rdstate () const +Return the state flags for this stream. The value is from the +enumeration @code{iostate}. You can test for any combination of + +@vtable @code +@item goodbit +There are no indications of exceptional states on this stream. + +@item eofbit +End of file. + +@item failbit +An operation has failed on this stream; this usually indicates bad +format of input. + +@item badbit +The stream is unusable. +@end vtable +@end deftypefn + +@deftypefn Method void ios::setstate (iostate @var{state}) +@findex ios::set +Set the state flag for this stream to @var{state} @emph{in addition to} +any state flags already set. Synonym (for upward compatibility): +@code{ios::set}. + +See @code{ios::clear} to set the stream state without regard to existing +state flags. See @code{ios::good}, @code{ios::eof}, @code{ios::fail}, +and @code{ios::bad}, to test the state. +@end deftypefn + +@deftypefn Method int ios::good () const +Test the state flags associated with this stream; true if no error +indicators are set. +@end deftypefn + +@deftypefn Method int ios::bad () const +Test whether a stream is marked as unusable. (Whether +@code{ios::badbit} is set.) +@end deftypefn + +@deftypefn Method int ios::eof () const +True if end of file was reached on this stream. (If @code{ios::eofbit} +is set.) +@end deftypefn + +@deftypefn Method int ios::fail () const +Test for any kind of failure on this stream: @emph{either} some +operation failed, @emph{or} the stream is marked as bad. (If either +@code{ios::failbit} or @code{ios::badbit} is set.) +@end deftypefn + +@deftypefn Method void ios::clear (iostate @var{state}) +@c FIXME-future: There is some complication to do with buffering and _throw_failure +Set the state indication for this stream to the argument @var{state}. +You may call @code{ios::clear} with no argument, in which case the state +is set to @code{good} (no errors pending). + +See @code{ios::good}, @code{ios::eof}, @code{ios::fail}, and +@code{ios::bad}, to test the state; see @code{ios::set} or +@code{ios::setstate} for an alternative way of setting the state. +@end deftypefn + +@node Format Control +@subsection Choices in formatting + +These methods control (or report on) settings for some details of +controlling streams, primarily to do with formatting output: + +@deftypefn Method char ios::fill () const +Report on the padding character in use. +@end deftypefn + +@deftypefn Method char ios::fill (char @var{padding}) +Set the padding character. You can also use the manipulator +@code{setfill}. @xref{Manipulators,,Changing stream properties in +expressions}. + +Default: blank. +@end deftypefn + +@deftypefn Method int ios::precision () const +Report the number of significant digits currently in use for output of +floating point numbers. + +Default: @code{6}. +@end deftypefn + +@deftypefn Method int ios::precision (int @var{signif}) +Set the number of significant digits (for input and output numeric +conversions) to @var{signif}. + +@findex setprecision +@cindex setting @code{ios::precision} +You can also use the manipulator @code{setprecision} for this purpose. +@xref{Manipulators,,Changing stream properties using manipulators}. +@end deftypefn + +@deftypefn Method int ios::width () const +Report the current output field width setting (the number of +characters to write on the next @samp{<<} output operation). + +Default: @code{0}, which means to use as many characters as necessary. +@end deftypefn + +@deftypefn Method int ios::width (int @var{num}) +Set the input field width setting to @var{num}. Return the +@emph{previous} value for this stream. + +@findex setw +@cindex setting @code{ios::width} +This value resets to zero (the default) every time you use @samp{<<}; it is +essentially an additional implicit argument to that operator. You can +also use the manipulator @code{setw} for this purpose. +@xref{Manipulators,,Changing stream properties using manipulators}. +@end deftypefn + +@need 2000 +@deftypefn Method fmtflags ios::flags () const +Return the current value of the complete collection of flags controlling +the format state. These are the flags and their meanings when set: + +@vtable @code +@item ios::dec +@itemx ios::oct +@itemx ios::hex +What numeric base to use in converting integers from internal to display +representation, or vice versa: decimal, octal, or hexadecimal, +respectively. (You can change the base using the manipulator +@code{setbase}, or any of the manipulators @code{dec}, @code{oct}, or +@code{hex}; @pxref{Manipulators,,Changing stream properties in +expressions}.) + +On input, if none of these flags is set, read numeric constants +according to the prefix: decimal if no prefix (or a @samp{.} suffix), +octal if a @samp{0} prefix is present, hexadecimal if a @samp{0x} prefix +is present. + +Default: @code{dec}. + +@item ios::fixed +Avoid scientific notation, and always show a fixed number of digits after +the decimal point, according to the output precision in effect. +Use @code{ios::precision} to set precision. + +@item ios::left +@itemx ios::right +@itemx ios::internal +Where output is to appear in a fixed-width field; left-justified, +right-justified, or with padding in the middle (e.g. between a numeric +sign and the associated value), respectively. + +@item ios::scientific +Use scientific (exponential) notation to display numbers. + +@item ios::showbase +Display the conventional prefix as a visual indicator of the conversion +base: no prefix for decimal, @samp{0} for octal, @samp{0x} for hexadecimal. + +@item ios::showpoint +Display a decimal point and trailing zeros after it to fill out numeric +fields, even when redundant. + +@item ios::showpos +Display a positive sign on display of positive numbers. + +@item ios::skipws +Skip white space. (On by default). + +@item ios::stdio +Flush the C @code{stdio} streams @code{stdout} and @code{stderr} after +each output operation (for programs that mix C and C++ output conventions). + +@item ios::unitbuf +Flush after each output operation. + +@item ios::uppercase +Use upper-case characters for the non-numeral elements in numeric +displays; for instance, @samp{0X7A} rather than @samp{0x7a}, or +@samp{3.14E+09} rather than @samp{3.14e+09}. +@end vtable +@end deftypefn + +@deftypefn Method fmtflags ios::flags (fmtflags @var{value}) +Set @var{value} as the complete collection of flags controlling the +format state. The flag values are described under @samp{ios::flags ()}. + +Use @code{ios::setf} or @code{ios::unsetf} to change one property at a +time. +@end deftypefn + +@deftypefn Method fmtflags ios::setf (fmtflags @var{flag}) +Set one particular flag (of those described for @samp{ios::flags ()}; +return the complete collection of flags @emph{previously} in effect. +(Use @code{ios::unsetf} to cancel.) +@end deftypefn + +@deftypefn Method fmtflags ios::setf (fmtflags @var{flag}, fmtflags @var{mask}) +Clear the flag values indicated by @var{mask}, then set any of them that +are also in @var{flag}. (Flag values are described for @samp{ios::flags +()}.) Return the complete collection of flags @emph{previously} in +effect. (See @code{ios::unsetf} for another way of clearing flags.) +@end deftypefn + +@deftypefn Method fmtflags ios::unsetf (fmtflags @var{flag}) +Make certain @var{flag} (a combination of flag values described for +@samp{ios::flags ()}) is not set for this stream; converse of +@code{ios::setf}. Returns the old values of those flags. +@c FIXME-future: should probably be fixed to give same result as setf. +@end deftypefn + +@node Manipulators +@subsection Changing stream properties using manipulators + +For convenience, @var{manipulators} provide a way to change certain +properties of streams, or otherwise affect them, in the middle of +expressions involving @samp{<<} or @samp{>>}. For example, you might +write + +@example +cout << "|" << setfill('*') << setw(5) << 234 << "|"; +@end example + +@noindent +to produce @samp{|**234|} as output. + +@deftypefn Manipulator {} ws +Skip whitespace. +@end deftypefn + +@deftypefn Manipulator {} flush +Flush an output stream. For example, @samp{cout << @dots{} <<flush;} +has the same effect as @samp{cout << @dots{}; cout.flush();}. +@end deftypefn + +@deftypefn Manipulator {} endl +Write an end of line character @samp{\n}, then flushes the output stream. +@end deftypefn + +@deftypefn Manipulator {} ends +Write @samp{\0} (the string terminator character). +@end deftypefn + +@deftypefn Manipulator {} setprecision (int @var{signif}) +You can change the value of @code{ios::precision} in @samp{<<} +expressions with the manipulator @samp{setprecision(@var{signif})}; for +example, + +@example +cout << setprecision(2) << 4.567; +@end example + +@noindent +prints @samp{4.6}. Requires @file{#include <iomanip.h>}. +@end deftypefn + +@deftypefn Manipulator {} setw (int @var{n}) +You can change the value of @code{ios::width} in @samp{<<} expressions +with the manipulator @samp{setw(@var{n})}; for example, + +@example +cout << setw(5) << 234; +@end example + +@noindent +prints @w{@samp{ 234}} with two leading blanks. Requires @file{#include +<iomanip.h>}. +@end deftypefn + +@deftypefn Manipulator {} setbase (int @var{base}) +Where @var{base} is one of @code{10} (decimal), @code{8} (octal), or +@code{16} (hexadecimal), change the base value for numeric +representations. Requires @file{#include <iomanip.h>}. +@end deftypefn + +@deftypefn Manipulator {} dec +Select decimal base; equivalent to @samp{setbase(10)}. +@end deftypefn + +@deftypefn Manipulator {} hex +Select hexadecimal base; equivalent to @samp{setbase(16)}. +@end deftypefn + +@deftypefn Manipulator {} oct +Select octal base; equivalent to @samp{setbase(8)}. +@end deftypefn + +@deftypefn Manipulator {} setfill (char @var{padding}) +Set the padding character, in the same way as @code{ios::fill}. +Requires @file{#include <iomanip.h>}. +@end deftypefn + +@node Extending +@subsection Extended data fields + +A related collection of methods allows you to extend this collection of +flags and parameters for your own applications, without risk of conflict +between them: + +@deftypefn Method {static fmtflags} ios::bitalloc () +Reserve a bit (the single bit on in the result) to use as a flag. Using +@code{bitalloc} guards against conflict between two packages that use +@code{ios} objects for different purposes. + +This method is available for upward compatibility, but is not in the +@sc{ansi} working paper. The number of bits available is limited; a +return value of @code{0} means no bit is available. +@end deftypefn + +@deftypefn Method {static int} ios::xalloc () +Reserve space for a long integer or pointer parameter. The result is a +unique nonnegative integer. You can use it as an index to +@code{ios::iword} or @code{ios::pword}. Use @code{xalloc} to arrange +for arbitrary special-purpose data in your @code{ios} objects, without +risk of conflict between packages designed for different purposes. +@end deftypefn + +@deftypefn Method long& ios::iword (int @var{index}) +Return a reference to arbitrary data, of long integer type, stored in an +@code{ios} instance. @var{index}, conventionally returned from +@code{ios::xalloc}, identifies what particular data you need. +@end deftypefn + +@deftypefn Method long ios::iword (int @var{index}) const +Return the actual value of a long integer stored in an @code{ios}. +@end deftypefn + +@deftypefn Method void*& ios::pword (int @var{index}) +Return a reference to an arbitrary pointer, stored in an @code{ios} +instance. @var{index}, originally returned from @code{ios::xalloc}, +identifies what particular pointer you need. +@end deftypefn + +@deftypefn Method void* ios::pword (int @var{index}) const +Return the actual value of a pointer stored in an @code{ios}. +@end deftypefn + +@node Synchronization +@subsection Synchronizing related streams + +You can use these methods to synchronize related streams with +one another: + +@deftypefn Method ostream* ios::tie () const +Report on what output stream, if any, is to be flushed before accessing +this one. A pointer value of @code{0} means no stream is tied. +@end deftypefn + +@deftypefn Method ostream* ios::tie (ostream* @var{assoc}) +Declare that output stream @var{assoc} must be flushed before accessing +this stream. +@end deftypefn + +@deftypefn Method int ios::sync_with_stdio ([int @var{switch}]) +Unless iostreams and C @code{stdio} are designed to work together, you +may have to choose between efficient C++ streams output and output +compatible with C @code{stdio}. Use @samp{ios::sync_with_stdio()} to +select C compatibility. + +The argument @var{switch} is a @sc{gnu} extension; use @code{0} as the +argument to choose output that is not necessarily compatible with C +@code{stdio}. The default value for @var{switch} is @code{1}. + +If you install the @code{stdio} implementation that comes with @sc{gnu} +@code{libio}, there are compatible input/output facilities for both C +and C++. In that situation, this method is unnecessary---but you may +still want to write programs that call it, for portability. +@end deftypefn + +@node Streambuf from Ios +@subsection Reaching the underlying @code{streambuf} + +Finally, you can use this method to access the underlying object: + +@deftypefn Method streambuf* ios::rdbuf () const +Return a pointer to the @code{streambuf} object that underlies this +@code{ios}. +@end deftypefn + +@node Ostream +@section Managing output streams: class @code{ostream} + +Objects of class @code{ostream} inherit the generic methods from +@code{ios}, and in addition have the following methods available. +Declarations for this class come from @file{iostream.h}. + +@deftypefn Constructor {} ostream::ostream () +The simplest form of the constructor for an @code{ostream} simply +allocates a new @code{ios} object. +@end deftypefn + +@deftypefn Constructor {} ostream::ostream (streambuf* @var{sb} @w{[, ostream} @var{tie}]) +This alternative constructor requires a first argument @var{sb} of type +@code{streambuf*}, to use an existing open stream for output. It also +accepts an optional second argument @var{tie}, to specify a related +@code{ostream*} as the initial value for @code{ios::tie}. + +If you give the @code{ostream} a @code{streambuf} explicitly, using +this constructor, the @var{sb} is @emph{not} destroyed (or deleted or +closed) when the @code{ostream} is destroyed. +@end deftypefn + +@menu +* Writing:: Writing on an ostream. +* Output Position:: Repositioning an ostream. +* Ostream Housekeeping:: Miscellaneous ostream utilities. +@end menu + +@node Writing +@subsection Writing on an @code{ostream} + +These methods write on an @code{ostream} (you may also use the operator +@code{<<}; @pxref{Operators,,Operators and Default Streams}). + +@deftypefn Method ostream& ostream::put (char @var{c}) +Write the single character @var{c}. +@end deftypefn + +@deftypefn Method ostream& ostream::write (@var{string}, int @var{length}) +Write @var{length} characters of a string to this @code{ostream}, +beginning at the pointer @var{string}. + +@var{string} may have any of these types: @code{char*}, @code{unsigned +char*}, @code{signed char*}. +@end deftypefn + +@deftypefn Method ostream& ostream::form (const char *@var{format}, ...) +A @sc{gnu} extension, similar to @code{fprintf(@var{file}, +@var{format}, ...)}. + +@var{format} is a @code{printf}-style format control string, which is used +to format the (variable number of) arguments, printing the result on +this @code{ostream}. See @code{ostream::vform} for a version that uses +an argument list rather than a variable number of arguments. +@end deftypefn + +@deftypefn Method ostream& ostream::vform (const char *@var{format}, va_list @var{args}) +A @sc{gnu} extension, similar to @code{vfprintf(@var{file}, +@var{format}, @var{args})}. + +@var{format} is a @code{printf}-style format control string, which is used +to format the argument list @var{args}, printing the result on +this @code{ostream}. See @code{ostream::form} for a version that uses a +variable number of arguments rather than an argument list. +@end deftypefn + +@node Output Position +@subsection Repositioning an @code{ostream} + +You can control the output position (on output streams that actually +support positions, typically files) with these methods: +@c FIXME-future: sort out which classes support this and which +@c don't; fstream, filebuf? And what is failure condition when not supported? + +@deftypefn Method streampos ostream::tellp () +Return the current write position in the stream. +@end deftypefn + +@deftypefn Method ostream& ostream::seekp (streampos @var{loc}) +Reset the output position to @var{loc} (which is usually the result of a +previous call to @code{ostream::tellp}). @var{loc} specifies an +absolute position in the output stream. +@end deftypefn + +@deftypefn Method ostream& ostream::seekp (streamoff @var{loc}, @var{rel}) +@findex ios::seekdir +Reset the output position to @var{loc}, relative to the beginning, end, +or current output position in the stream, as indicated by @var{rel} (a +value from the enumeration @code{ios::seekdir}): + +@vtable @code +@item beg +Interpret @var{loc} as an absolute offset from the beginning of the +file. + +@item cur +Interpret @var{loc} as an offset relative to the current output +position. + +@item end +Interpret @var{loc} as an offset from the current end of the output +stream. +@end vtable +@end deftypefn + +@node Ostream Housekeeping +@subsection Miscellaneous @code{ostream} utilities + +You may need to use these @code{ostream} methods for housekeeping: + +@deftypefn Method ostream& flush () +Deliver any pending buffered output for this @code{ostream}. +@end deftypefn + +@deftypefn Method int ostream::opfx () +@code{opfx} is a @dfn{prefix} method for operations on @code{ostream} +objects; it is designed to be called before any further processing. See +@code{ostream::osfx} for the converse. +@c FIXME-future: specify sometime which methods start with opfx. + +@code{opfx} tests that the stream is in state @code{good}, and if so +flushes any stream tied to this one. + +The result is @code{1} when @code{opfx} succeeds; else (if the stream state is +not @code{good}), the result is @code{0}. +@end deftypefn + +@deftypefn Method void ostream::osfx () +@code{osfx} is a @dfn{suffix} method for operations on @code{ostream} +objects; it is designed to be called at the conclusion of any processing. All +the @code{ostream} methods end by calling @code{osfx}. See +@code{ostream::opfx} for the converse. + +If the @code{unitbuf} flag is set for this stream, @code{osfx} flushes +any buffered output for it. + +If the @code{stdio} flag is set for this stream, @code{osfx} flushes any +output buffered for the C output streams @file{stdout} and @file{stderr}. +@end deftypefn + +@node Istream +@section Managing input streams: class @code{istream} + +Class @code{istream} objects are specialized for input; as for +@code{ostream}, they are derived from @code{ios}, so you can use any of +the general-purpose methods from that base class. Declarations for this +class also come from @file{iostream.h}. + +@deftypefn Constructor {} istream::istream () +When used without arguments, the @code{istream} constructor simply +allocates a new @code{ios} object and initializes the input counter (the +value reported by @code{istream::gcount}) to @code{0}. +@end deftypefn + +@deftypefn Constructor {} istream::istream (streambuf *@var{sb} @w{[, ostream} @var{tie}]) +You can also call the constructor with one or two arguments. The first +argument @var{sb} is a @code{streambuf*}; if you supply this pointer, +the constructor uses that @code{streambuf} for input. +You can use the second optional argument @var{tie} to specify a related +output stream as the initial value for @code{ios::tie}. + +If you give the @code{istream} a @code{streambuf} explicitly, using +this constructor, the @var{sb} is @emph{not} destroyed (or deleted or +closed) when the @code{ostream} is destroyed. +@end deftypefn + +@menu +* Char Input:: Reading one character. +* String Input:: Reading strings. +* Input Position:: Repositioning an istream. +* Istream Housekeeping:: Miscellaneous istream utilities. +@end menu + +@node Char Input +@subsection Reading one character + +Use these methods to read a single character from the input stream: + +@deftypefn Method int istream::get () +Read a single character (or @code{EOF}) from the input stream, returning +it (coerced to an unsigned char) as the result. +@end deftypefn + +@deftypefn Method istream& istream::get (char& @var{c}) +Read a single character from the input stream, into @code{&@var{c}}. +@end deftypefn + +@deftypefn Method int istream::peek () +Return the next available input character, but @emph{without} changing +the current input position. +@end deftypefn + +@node String Input +@subsection Reading strings + +Use these methods to read strings (for example, a line at a time) from +the input stream: + +@deftypefn Method istream& istream::get (char* @var{c}, int @var{len} @w{[, char} @var{delim}]) +Read a string from the input stream, into the array at @var{c}. + +The remaining arguments limit how much to read: up to @samp{len-1} +characters, or up to (but not including) the first occurrence in the +input of a particular delimiter character @var{delim}---newline +(@code{\n}) by default. (Naturally, if the stream reaches end of file +first, that too will terminate reading.) + +If @var{delim} was present in the input, it remains available as if +unread; to discard it instead, see @code{iostream::getline}. + +@code{get} writes @samp{\0} at the end of the string, regardless +of which condition terminates the read. +@end deftypefn + +@deftypefn Method istream& istream::get (streambuf& @var{sb} @w{[, char} @var{delim}]) +Read characters from the input stream and copy them on the +@code{streambuf} object @var{sb}. Copying ends either just before the +next instance of the delimiter character @var{delim} (newline @code{\n} +by default), or when either stream ends. If @var{delim} was present in +the input, it remains available as if unread. +@end deftypefn + +@deftypefn Method istream& istream::getline (@var{charptr}, int @var{len} @w{[, char} @var{delim}]) +Read a line from the input stream, into the array at @var{charptr}. +@var{charptr} may be any of three kinds of pointer: @code{char*}, +@code{unsigned char*}, or @code{signed char*}. + +The remaining arguments limit how much to read: up to (but not +including) the first occurrence in the input of a line delimiter +character @var{delim}---newline (@code{\n}) by default, or up to +@samp{len-1} characters (or to end of file, if that happens sooner). + +If @code{getline} succeeds in reading a ``full line'', it also discards +the trailing delimiter character from the input stream. (To preserve it +as available input, see the similar form of @code{iostream::get}.) + +If @var{delim} was @emph{not} found before @var{len} characters or end +of file, @code{getline} sets the @code{ios::fail} flag, as well as the +@code{ios::eof} flag if appropriate. + +@code{getline} writes a null character at the end of the string, regardless +of which condition terminates the read. +@end deftypefn + +@deftypefn Method istream& istream::read (@var{pointer}, int @var{len}) +Read @var{len} bytes into the location at @var{pointer}, unless the +input ends first. + +@var{pointer} may be of type @code{char*}, @code{void*}, @code{unsigned +char*}, or @code{signed char*}. + +If the @code{istream} ends before reading @var{len} bytes, @code{read} +sets the @code{ios::fail} flag. +@end deftypefn + +@deftypefn Method istream& istream::gets (char **@var{s} @w{[, char} @var{delim}]) +A @sc{gnu} extension, to read an arbitrarily long string +from the current input position to the next instance of the @var{delim} +character (newline @code{\n} by default). + +To permit reading a string of arbitrary length, @code{gets} allocates +whatever memory is required. Notice that the first argument @var{s} is +an address to record a character pointer, rather than the pointer +itself. +@end deftypefn + +@deftypefn Method istream& istream::scan (const char *format ...) +A @sc{gnu} extension, similar to @code{fscanf(@var{file}, +@var{format}, ...)}. The @var{format} is a @code{scanf}-style format +control string, which is used to read the variables in the remainder of +the argument list from the @code{istream}. +@end deftypefn + +@deftypefn Method istream& istream::vscan (const char *format, va_list args) +Like @code{istream::scan}, but takes a single @code{va_list} argument. +@end deftypefn + +@node Input Position +@subsection Repositioning an @code{istream} + +Use these methods to control the current input position: + +@deftypefn Method streampos istream::tellg () +Return the current read position, so that you can save it and return to +it later with @code{istream::seekg}. +@end deftypefn + +@deftypefn Method istream& istream::seekg (streampos @var{p}) +Reset the input pointer (if the input device permits it) to @var{p}, +usually the result of an earlier call to @code{istream::tellg}. +@end deftypefn + +@deftypefn Method istream& istream::seekg (streamoff @var{offset}, ios::seek_dir @var{ref}) +Reset the input pointer (if the input device permits it) to @var{offset} +characters from the beginning of the input, the current position, or the +end of input. Specify how to interpret @var{offset} with one of these +values for the second argument: + +@vtable @code +@item ios::beg +Interpret @var{loc} as an absolute offset from the beginning of the +file. + +@item ios::cur +Interpret @var{loc} as an offset relative to the current output +position. + +@item ios::end +Interpret @var{loc} as an offset from the current end of the output +stream. +@end vtable +@end deftypefn + +@node Istream Housekeeping +@subsection Miscellaneous @code{istream} utilities + +Use these methods for housekeeping on @code{istream} objects: + +@deftypefn Method int istream::gcount () +Report how many characters were read from this @code{istream} in the +last unformatted input operation. +@c FIXME! Define "unformatted input" somewhere... +@end deftypefn + +@deftypefn Method int istream::ipfx (int @var{keepwhite}) +Ensure that the @code{istream} object is ready for reading; check for +errors and end of file and flush any tied stream. @code{ipfx} skips +whitespace if you specify @code{0} as the @var{keepwhite} +argument, @emph{and} @code{ios::skipws} is set for this stream. + +To avoid skipping whitespace (regardless of the @code{skipws} setting on +the stream), use @code{1} as the argument. + +Call @code{istream::ipfx} to simplify writing your own methods for reading +@code{istream} objects. +@end deftypefn + +@deftypefn Method void istream::isfx () +A placeholder for compliance with the draft @sc{ansi} standard; this +method does nothing whatever. + +If you wish to write portable standard-conforming code on @code{istream} +objects, call @code{isfx} after any operation that reads from an +@code{istream}; if @code{istream::ipfx} has any special effects that +must be cancelled when done, @code{istream::isfx} will cancel them. +@end deftypefn + +@deftypefn Method istream& istream::ignore ([int @var{n}] @w{[, int} @var{delim}]) +Discard some number of characters pending input. The first optional +argument @var{n} specifies how many characters to skip. The second +optional argument @var{delim} specifies a ``boundary'' character: +@code{ignore} returns immediately if this character appears in the +input. + +By default, @var{delim} is @code{EOF}; that is, if you do not specify a +second argument, only the count @var{n} restricts how much to ignore +(while input is still available). + +If you do not specify how many characters to ignore, @code{ignore} +returns after discarding only one character. +@end deftypefn + +@deftypefn Method istream& istream::putback (char @var{ch}) +Attempts to back up one character, replacing the character backed-up +over by @var{ch}. Returns @code{EOF} if this is not allowed. Putting +back the most recently read character is always allowed. (This method +corresponds to the C function @code{ungetc}.) +@end deftypefn + +@deftypefn Method istream& istream::unget () +Attempt to back up one character. +@end deftypefn + +@node Iostream +@section Input and output together: class @code{iostream} + +If you need to use the same stream for input and output, you can use an +object of the class @code{iostream}, which is derived from @emph{both} +@code{istream} and @code{ostream}. + +The constructors for @code{iostream} behave just like the constructors +for @code{istream}. + +@deftypefn Constructor {} iostream::iostream () +When used without arguments, the @code{iostream} constructor simply +allocates a new @code{ios} object, and initializes the input counter +(the value reported by @code{istream::gcount}) to @code{0}. +@end deftypefn + +@deftypefn Constructor {} iostream::iostream (streambuf* @var{sb} @w{[, ostream*} @var{tie}]) +You can also call a constructor with one or two arguments. The first +argument @var{sb} is a @code{streambuf*}; if you supply this pointer, +the constructor uses that @code{streambuf} for input and output. + +You can use the optional second argument @var{tie} (an @code{ostream*}) +to specify a related output stream as the initial value for +@code{ios::tie}. +@end deftypefn + +@cindex @code{iostream} destructor +@cindex destructor for @code{iostream} +As for @code{ostream} and @code{istream}, @code{iostream} simply uses +the @code{ios} destructor. However, an @code{iostream} is not deleted by +its destructor. + +You can use all the @code{istream}, @code{ostream}, and @code{ios} +methods with an @code{iostream} object. + +@node Files and Strings +@chapter Classes for Files and Strings + +There are two very common special cases of input and output: using files, +and using strings in memory. + +@code{libio} defines four specialized classes for these cases: + +@ftable @code +@item ifstream +Methods for reading files. + +@item ofstream +Methods for writing files. + +@item istrstream +Methods for reading strings from memory. + +@item ostrstream +Methods for writing strings in memory. +@end ftable + +@menu +* Files:: Reading and writing files. +* Strings:: Reading and writing strings in memory. +@end menu + +@node Files +@section Reading and writing files + +These methods are declared in @file{fstream.h}. + +@findex ifstream +@cindex class @code{ifstream} +You can read data from class @code{ifstream} with any operation from class +@code{istream}. There are also a few specialized facilities: + +@deftypefn Constructor {} ifstream::ifstream () +Make an @code{ifstream} associated with a new file for input. (If you +use this version of the constructor, you need to call +@code{ifstream::open} before actually reading anything) +@end deftypefn + +@deftypefn Constructor {} ifstream::ifstream (int @var{fd}) +Make an @code{ifstream} for reading from a file that was already open, +using file descriptor @var{fd}. (This constructor is compatible with +other versions of iostreams for @sc{posix} systems, but is not part of +the @sc{ansi} working paper.) +@end deftypefn + +@deftypefn Constructor {} ifstream::ifstream (const char* @var{fname} @w{[, int} @var{mode} @w{[, int} @var{prot}]]) +Open a file @code{*@var{fname}} for this @code{ifstream} object. + +By default, the file is opened for input (with @code{ios::in} as +@var{mode}). If you use this constructor, the file will be closed when +the @code{ifstream} is destroyed. + +You can use the optional argument @var{mode} to specify how to open the +file, by combining these enumerated values (with @samp{|} bitwise or). +(These values are actually defined in class @code{ios}, so that all +file-related streams may inherit them.) Only some of these modes are +defined in the latest draft @sc{ansi} specification; if portability is +important, you may wish to avoid the others. + +@vtable @code +@item ios::in +Open for input. (Included in @sc{ansi} draft.) + +@item ios::out +Open for output. (Included in @sc{ansi} draft.) + +@item ios::ate +Set the initial input (or output) position to the end of the file. + +@item ios::app +Seek to end of file before each write. (Included in @sc{ansi} draft.) + +@item ios::trunc +Guarantee a fresh file; discard any contents that were previously +associated with it. + +@item ios::nocreate +Guarantee an existing file; fail if the specified file did not already +exist. + +@item ios::noreplace +Guarantee a new file; fail if the specified file already existed. + +@item ios::bin +Open as a binary file (on systems where binary and text files have different +properties, typically how @samp{\n} is mapped; included in @sc{ansi} draft). +@end vtable + +@noindent +The last optional argument @var{prot} is specific to Unix-like systems; +it specifies the file protection (by default @samp{644}). +@end deftypefn + +@deftypefn Method void ifstream::open (const char* @var{fname} @w{[, int} @var{mode} @w{[, int} @var{prot}]]) +Open a file explicitly after the associated @code{ifstream} object +already exists (for instance, after using the default constructor). The +arguments, options and defaults all have the same meanings as in the +fully specified @code{ifstream} constructor. +@end deftypefn + +@findex ostream +@cindex class @code{ostream} +You can write data to class @code{ofstream} with any operation from class +@code{ostream}. There are also a few specialized facilities: + +@deftypefn Constructor {} ofstream::ofstream () +Make an @code{ofstream} associated with a new file for output. +@end deftypefn + +@deftypefn Constructor {} ofstream::ofstream (int @var{fd}) +Make an @code{ofstream} for writing to a file that was already open, +using file descriptor @var{fd}. +@end deftypefn + +@deftypefn Constructor {} ofstream::ofstream (const char* @var{fname} @w{[, int} @var{mode} @w{[, int} @var{prot}]]) +Open a file @code{*@var{fname}} for this @code{ofstream} object. + +By default, the file is opened for output (with @code{ios::out} as @var{mode}). +You can use the optional argument @var{mode} to specify how to open the +file, just as described for @code{ifstream::ifstream}. + +The last optional argument @var{prot} specifies the file protection (by +default @samp{644}). +@end deftypefn + +@deftypefn Destructor {} ofstream::~ofstream () +The files associated with @code{ofstream} objects are closed when the +corresponding object is destroyed. +@end deftypefn + +@deftypefn Method void ofstream::open (const char* @var{fname} @w{[, int} @var{mode} @w{[, int} @var{prot}]]) +Open a file explicitly after the associated @code{ofstream} object +already exists (for instance, after using the default constructor). The +arguments, options and defaults all have the same meanings as in the +fully specified @code{ofstream} constructor. +@end deftypefn + +@findex fstream +@cindex class @code{fstream} +The class @code{fstream} combines the facilities of @code{ifstream} and +@code{ofstream}, just as @code{iostream} combines @code{istream} and +@code{ostream}. + +@c FIXME-future: say something about fstream constructor, maybe. + +@findex fstreambase +@cindex class @code{fstreambase} +The class @code{fstreambase} underlies both @code{ifstream} and +@code{ofstream}. They both inherit this additional method: + +@deftypefn Method void fstreambase::close () +Close the file associated with this object, and set @code{ios::fail} in +this object to mark the event. +@end deftypefn + +@node Strings +@section Reading and writing in memory + +@c FIXME!! Per, there's a lot of guesswork here---please check carefully! + +@findex istrstream +@cindex class @code{istrstream} +@findex ostrstream +@cindex class @code{ostrstream} +@findex strstream +@cindex class @code{strstream} +@findex strstreambase +@cindex class @code{strstreambase} +@findex strstreambuf +@cindex class @code{strstreambuf} +The classes @code{istrstream}, @code{ostrstream}, and @code{strstream} +provide some additional features for reading and writing strings in +memory---both static strings, and dynamically allocated strings. The +underlying class @code{strstreambase} provides some features common to +all three; @code{strstreambuf} underlies that in turn. + +@c FIXME-future: Document strstreambuf methods one day, when we document +@c streambuf more fully. + +@deftypefn Constructor {} istrstream::istrstream (const char* @var{str} @w{[, int} @var{size}]) +Associate the new input string class @code{istrstream} with an existing +static string starting at @var{str}, of size @var{size}. If you do not +specify @var{size}, the string is treated as a @code{NUL} terminated string. +@end deftypefn + +@deftypefn Constructor {} ostrstream::ostrstream () +Create a new stream for output to a dynamically managed string, which +will grow as needed. +@end deftypefn + +@deftypefn Constructor {} ostrstream::ostrstream (char* @var{str}, int @var{size} [,int @var{mode}]) +A new stream for output to a statically defined string of length +@var{size}, starting at @var{str}. You may optionally specify one of +the modes described for @code{ifstream::ifstream}; if you do not specify +one, the new stream is simply open for output, with mode @code{ios::out}. +@end deftypefn + +@deftypefn Method int ostrstream::pcount () +Report the current length of the string associated with this @code{ostrstream}. +@end deftypefn + +@deftypefn Method char* ostrstream::str () +A pointer to the string managed by this @code{ostrstream}. Implies +@samp{ostrstream::freeze()}. + +Note that if you want the string to be nul-terminated, +you must do that yourself (perhaps by writing ends to the stream). +@end deftypefn + +@deftypefn Method void ostrstream::freeze ([int @var{n}]) +If @var{n} is nonzero (the default), declare that the string associated +with this @code{ostrstream} is not to change dynamically; while frozen, +it will not be reallocated if it needs more space, and it will not be +deallocated when the @code{ostrstream} is destroyed. Use +@samp{freeze(1)} if you refer to the string as a pointer after creating +it via @code{ostrstream} facilities. + +@samp{freeze(0)} cancels this declaration, allowing a dynamically +allocated string to be freed when its @code{ostrstream} is destroyed. + +If this @code{ostrstream} is already static---that is, if it was created +to manage an existing statically allocated string---@code{freeze} is +unnecessary, and has no effect. +@end deftypefn + +@deftypefn Method int ostrstream::frozen () +Test whether @code{freeze(1)} is in effect for this string. +@end deftypefn + +@deftypefn Method strstreambuf* strstreambase::rdbuf () +A pointer to the underlying @code{strstreambuf}. +@end deftypefn + +@node Streambuf +@chapter Using the @code{streambuf} Layer + +The @code{istream} and @code{ostream} classes are meant to handle +conversion between objects in your program and their textual representation. + +By contrast, the underlying @code{streambuf} class is for transferring +raw bytes between your program, and input sources or output sinks. +Different @code{streambuf} subclasses connect to different kinds of +sources and sinks. + +The @sc{gnu} implementation of @code{streambuf} is still evolving; we +describe only some of the highlights. + +@menu +* Areas:: Areas in a streambuf. +* Overflow:: Simple output re-direction +* Formatting:: C-style formatting for streambuf objects. +* Stdiobuf:: Wrappers for C stdio. +* Procbuf:: Reading/writing from/to a pipe +* Backing Up:: Marking and returning to a position. +* Indirectbuf:: Forwarding I/O activity. +@end menu + +@node Areas +@section Areas of a @code{streambuf} + +Streambuf buffer management is fairly sophisticated (this is a +nice way to say ``complicated''). The standard protocol +has the following ``areas'': + +@itemize @bullet +@item +@cindex put area +The @dfn{put area} contains characters waiting for output. + +@item +@cindex get area +The @dfn{get area} contains characters available for reading. +@end itemize + +The @sc{gnu} @code{streambuf} design extends this, but the details are +still evolving. + +The following methods are used to manipulate these areas. +These are all protected methods, which are intended to be +used by virtual function in classes derived from @code{streambuf}. +They are also all ANSI/ISO-standard, and the ugly names +are traditional. +(Note that if a pointer points to the 'end' of an area, +it means that it points to the character after the area.) + +@deftypefn Method char* streambuf::pbase () const +Returns a pointer to the start of the put area. +@end deftypefn + +@deftypefn Method char* streambuf::epptr () const +Returns a pointer to the end of the put area. +@end deftypefn + +@deftypefn Method char* streambuf::pptr () const +If @code{pptr() < epptr ()}, the @code{pptr()} +returns a pointer to the current put position. +(In that case, the next write will +overwrite @code{*pptr()}, and increment @code{pptr()}.) +Otherwise, there is no put position available +(and the next character written will cause @code{streambuf::overflow} +to be called). +@end deftypefn + +@deftypefn Method void streambuf::pbump (int @var{N}) +Add @var{N} to the current put pointer. +No error checking is done. +@end deftypefn + +@deftypefn Method void streambuf::setp (char* @var{P}, char* @var{E}) +Sets the start of the put area to @var{P}, the end of the put area to @var{E}, +and the current put pointer to @var{P} (also). +@end deftypefn + +@deftypefn Method char* streambuf::eback () const +Returns a pointer to the start of the get area. +@end deftypefn + +@deftypefn Method char* streambuf::egptr () const +Returns a pointer to the end of the get area. +@end deftypefn + +@deftypefn Method char* streambuf::gptr () const +If @code{gptr() < egptr ()}, then @code{gptr()} +returns a pointer to the current get position. +(In that case the next read will read @code{*gptr()}, +and possibly increment @code{gptr()}.) +Otherwise, there is no read position available +(and the next read will cause @code{streambuf::underflow} +to be called). +@end deftypefn + +@deftypefn Method void streambuf:gbump (int @var{N}) +Add @var{N} to the current get pointer. +No error checking is done. +@end deftypefn + +@deftypefn Method void streambuf::setg (char* @var{B}, char* @var{P}, char* @var{E}) +Sets the start of the get area to @var{B}, the end of the get area to @var{E}, +and the current put pointer to @var{P}. +@end deftypefn + +@node Overflow +@section Simple output re-direction by redefining @code{overflow} + +Suppose you have a function @code{write_to_window} that +writes characters to a @code{window} object. If you want to use the +ostream function to write to it, here is one (portable) way to do it. +This depends on the default buffering (if any). + +@cartouche +@smallexample +#include <iostream.h> +/* Returns number of characters successfully written to @var{win}. */ +extern int write_to_window (window* win, char* text, int length); + +class windowbuf : public streambuf @{ + window* win; + public: + windowbuf (window* w) @{ win = w; @} + int sync (); + int overflow (int ch); + // Defining xsputn is an optional optimization. + // (streamsize was recently added to ANSI C++, not portable yet.) + streamsize xsputn (char* text, streamsize n); +@}; + +int windowbuf::sync () +@{ streamsize n = pptr () - pbase (); + return (n && write_to_window (win, pbase (), n) != n) ? EOF : 0; +@} + +int windowbuf::overflow (int ch) +@{ streamsize n = pptr () - pbase (); + if (n && sync ()) + return EOF; + if (ch != EOF) + @{ + char cbuf[1]; + cbuf[0] = ch; + if (write_to_window (win, cbuf, 1) != 1) + return EOF; + @} + pbump (-n); // Reset pptr(). + return 0; +@} + +streamsize windowbuf::xsputn (char* text, streamsize n) +@{ return sync () == EOF ? 0 : write_to_window (win, text, n); @} + +int +main (int argc, char**argv) +@{ + window *win = ...; + windowbuf wbuf(win); + ostream wstr(&wbuf); + wstr << "Hello world!\n"; +@} +@end smallexample +@end cartouche + + + +@node Formatting +@section C-style formatting for @code{streambuf} objects + +The @sc{gnu} @code{streambuf} class supports @code{printf}-like +formatting and scanning. + +@deftypefn Method int streambuf::form (const char *@var{format}, ...) +Similar to @code{fprintf(@var{file}, @var{format}, ...)}. +The @var{format} is a @code{printf}-style format control string, which is used +to format the (variable number of) arguments, printing the result on +the @code{this} streambuf. The result is the number of characters printed. +@end deftypefn + +@deftypefn Method int streambuf::vform (const char *@var{format}, va_list @var{args}) +Similar to @code{vfprintf(@var{file}, @var{format}, @var{args})}. +The @var{format} is a @code{printf}-style format control string, which is used +to format the argument list @var{args}, printing the result on +the @code{this} streambuf. The result is the number of characters printed. +@end deftypefn + +@deftypefn Method int streambuf::scan (const char *@var{format}, ...) +Similar to @code{fscanf(@var{file}, @var{format}, ...)}. +The @var{format} is a @code{scanf}-style format control string, which is used +to read the (variable number of) arguments from the @code{this} streambuf. +The result is the number of items assigned, or @code{EOF} in case of +input failure before any conversion. +@end deftypefn + +@deftypefn Method int streambuf::vscan (const char *@var{format}, va_list @var{args}) +Like @code{streambuf::scan}, but takes a single @code{va_list} argument. +@end deftypefn + +@node Stdiobuf +@section Wrappers for C @code{stdio} + +A @dfn{stdiobuf} is a @code{streambuf} object that points to +a @code{FILE} object (as defined by @code{stdio.h}). +All @code{streambuf} operations on the @code{stdiobuf} are forwarded +to the @code{FILE}. Thus the @code{stdiobuf} object provides a +wrapper around a @code{FILE}, allowing use of @code{streambuf} +operations on a @code{FILE}. This can be useful when mixing +C code with C++ code. + +The pre-defined streams @code{cin}, @code{cout}, and @code{cerr} are +normally implemented as @code{stdiobuf} objects that point to +respectively @code{stdin}, @code{stdout}, and @code{stderr}. This is +convenient, but it does cost some extra overhead. + +If you set things up to use the implementation of @code{stdio} provided +with this library, then @code{cin}, @code{cout}, and @code{cerr} will be +set up to to use @code{stdiobuf} objects, since you get their benefits +for free. @xref{Stdio,,C Input and Output}. + +@ignore +@c FIXME-future: setbuf is not yet documented, hence this para is not useful. +Note that if you use @code{setbuf} to give a buffer to a @code{stdiobuf}, +that buffer will provide intermediate buffering in addition that +whatever is done by the @code{FILE}. +@end ignore + +@node Procbuf +@section Reading/writing from/to a pipe + +The @dfn{procbuf} class is a @sc{gnu} extension. It is derived from +@code{streambuf}. A @code{procbuf} can be @dfn{closed} (in which case +it does nothing), or @dfn{open} (in which case it allows communicating +through a pipe with some other program). + +@deftypefn Constructor {} procbuf::procbuf () +Creates a @code{procbuf} in a @dfn{closed} state. +@end deftypefn + +@deftypefn Method procbuf* procbuf::open (const char *@var{command}, int @var{mode}) +Uses the shell (@file{/bin/sh}) to run a program specified by @var{command}. + +If @var{mode} is @samp{ios::in}, standard output from the program is sent +to a pipe; you can read from the pipe by reading from the +@code{procbuf}. (This is similar to @w{@samp{popen(@var{command}, "r")}}.) + +If @var{mode} is @samp{ios::out}, output written written to the +@code{procbuf} is written to a pipe; the program is set up to read its +standard input from (the other end of) the pipe. (This is similar to +@w{@samp{popen(@var{command}, "w")}}.) + +The @code{procbuf} must start out in the @dfn{closed} state. +Returns @samp{*this} on success, and @samp{NULL} on failure. +@end deftypefn + +@deftypefn Constructor {} procbuf::procbuf (const char *@var{command}, int @var{mode}) +Calls @samp{procbuf::open (@var{command}, @var{mode})}. +@end deftypefn + +@deftypefn Method procbuf* procbuf::close () +Waits for the program to finish executing, +and then cleans up the resources used. +Returns @samp{*this} on success, and @samp{NULL} on failure. +@end deftypefn + +@deftypefn Destructor {} procbuf::~procbuf () +Calls @samp{procbuf::close}. +@end deftypefn + +@node Backing Up +@section Backing up + +The @sc{gnu} iostream library allows you to ask a @code{streambuf} to +remember the current position. This allows you to go back to this +position later, after reading further. You can back up arbitrary +amounts, even on unbuffered files or multiple buffers' worth, as long as +you tell the library in advance. This unbounded backup is very useful +for scanning and parsing applications. This example shows a typical +scenario: + +@cartouche +@smallexample +// 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 none 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": Back up 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: Back up 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: Back up and signal failure. + sb->seekmark(fence); // Backup to 'fence' + return -1; +@} +@end smallexample +@end cartouche + +@deftypefn Constructor {} streammarker::streammarker (streambuf* @var{sbuf}) +Create a @code{streammarker} associated with @var{sbuf} +that remembers the current position of the get pointer. +@end deftypefn + +@deftypefn Method int streammarker::delta (streammarker& @var{mark2}) +Return the difference between the get positions corresponding +to @code{*this} and @var{mark2} (which must point into the same +@code{streambuffer} as @code{this}). +@end deftypefn + +@deftypefn Method int streammarker::delta () +Return the position relative to the streambuffer's current get position. +@end deftypefn + +@deftypefn Method int streambuf::seekmark (streammarker& @var{mark}) +Move the get pointer to where it (logically) was when @var{mark} +was constructed. +@end deftypefn + +@node Indirectbuf +@section Forwarding I/O activity + +An @dfn{indirectbuf} is one that forwards all of its I/O requests +to another streambuf. + +@ignore +@c FIXME-future: get_stream and put_stream are so far undocumented. +All get-related requests are sent to get_stream(). +All put-related requests are sent to put_stream(). +@end ignore + +An @code{indirectbuf} can be used to implement Common Lisp +synonym-streams and two-way-streams: + +@example +class synonymbuf : public indirectbuf @{ + Symbol *sym; + synonymbuf(Symbol *s) @{ sym = s; @} + virtual streambuf *lookup_stream(int mode) @{ + return coerce_to_streambuf(lookup_value(sym)); @} +@}; +@end example + +@node Stdio +@chapter C Input and Output + +@code{libio} is distributed with a complete implementation of the ANSI C +@code{stdio} facility. It is implemented using @code{streambuf} +objects. @xref{Stdiobuf,,Wrappers for C @code{stdio}}. + +The @code{stdio} package is intended as a replacement for the whatever +@code{stdio} is in your C library. +@ignore +@c FIXME-future: This is not useful unless we specify what problems. +It can co-exist with C libraries that have alternate implementations of +stdio, but there may be some problems. +@end ignore +Since @code{stdio} works best when you build @code{libc} to contain it, and +that may be inconvenient, it is not installed by default. + +Extensions beyond @sc{ansi}: + +@itemize @bullet +@item +A stdio @code{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. + +@item +If you create a new streambuf sub-class (in C++), you can use it as a +@code{FILE} from C. Thus the system is extensible using the standard +@code{streambuf} protocol. + +@item +You can arbitrarily mix reading and writing, without having to seek +in between. + +@item +Unbounded @code{ungetc()} buffer. +@end itemize + +@ignore +@c FIXME-future: Per says this is not ready to go public at v0.5 +@node Libio buffer management +@chapter Libio buffer management + +The libio user functions present an abstract sequence of characters, +that they read and write from. A number of buffers are used to go +between the user program and the abstract sequence. These buffers are +concrete arrays of characters that contain some sub-sequence of the +abstract sequence. + +The libio buffer management protocol is fairly complex. Its design is +based on the C++ @code{streambuf} protocol, so that the C++ +@code{streambuf} classes can be trivially implemented on top of the +libio protocol. + +The @dfn{write area} contains characters waiting for output. + +The @dfn{read area} contains characters available for reading. + +The @dfn{reserve area} is available to virtual methods. +Usually, the get and/or put areas are part of the reserve area. + +The @dfn{main get area} contains characters that have +been read in from the character source, but not yet +read by the application. + +The @dfn{backup area} contains previously read data that is being saved +because of a user request, or that have been "unread" (put back). +@end ignore + +@ignore +@c Per says this design is not finished +@node Streambuf internals +@chapter Streambuf internals + +@menu +* Buffer management:: +* Filebuf internals:: +@end menu + +@node Buffer management +@section Buffer management + +@subsection Areas + +NOTE: This chapter is due for an update. + +Streambuf buffer management is fairly sophisticated (this is a +nice way to say "complicated"). The standard protocol +has the following "areas": + +@itemize @bullet +@cindex put area +@item +The @dfn{put area} contains characters waiting for output. +@cindex get area +@item +The @dfn{get area} contains characters available for reading. +@cindex reserve area +@item +The @dfn{reserve area} is available to virtual methods. +Usually, the get and/or put areas are part of the reserve area. +@end itemize + +The @sc{gnu} @code{streambuf} design extends this by supporting two +get areas: +@itemize @bullet +@cindex main get area +@item +The @dfn{main get area} contains characters that have +been read in from the character source, but not yet +read by the application. +@cindex backup area +@item +The @dfn{backup area} contains previously read data that is being +saved because of a user request, or that have been "unread" (putback). +@end itemize + +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 @dfn{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 @dfn{non-current get area}. + +@subsection Pointers + +The following @code{char*} pointers define the various areas. + +@deftypefn Method char* streambuf::base () +The start of the reserve area. +@end deftypefn + +@deftypefn Method char* streambuf::ebuf () +The end of the reserve area. +@end deftypefn + +@deftypefn Method char* streambuf::Gbase () +The start of the main get area. +@end deftypefn + +@deftypefn Method char* streambuf::eGptr () +The end of the main get area. +@end deftypefn + +@deftypefn Method char* streambuf::Bbase () +The start of the backup area. +@end deftypefn + +@deftypefn Method char* streambuf::Bptr () +The start of the used part of the backup area. +The area (@code{Bptr()} .. @code{eBptr()}) contains data that has been +pushed back, while (@code{Bbase()} .. @code{eBptr()}) contains unused +space available for future putbacks. +@end deftypefn + +@deftypefn Method char* streambuf::eBptr () +The end of the backup area. +@end deftypefn + +@deftypefn Method char* streambuf::Nbase () +The start of the non-current get area (either @code{main_gbase} or @code{backup_gbase}). +@end deftypefn + +@deftypefn Method char* streambuf::eNptr () +The end of the non-current get area. +@end deftypefn + +@node Filebuf internals +@section Filebuf internals + +The @code{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. + +@subsection Tied read and write pointers + +The streambuf model allows completely independent read and write pointers. +However, a @code{filebuf} has only a single logical pointer used +for both reads and writes. Since the @code{streambuf} protocol +uses @code{gptr()} for reading and @code{pptr()} for writing, +we map the logical file pointer into either @code{gptr()} or @code{pptr()} +at different times. + +@itemize @bullet +@item +Reading is allowed when @code{gptr() < egptr()}, which we call get mode. + +@item +Writing is allowed when @code{pptr() < epptr()}, which we call put mode. +@end itemize + +@noindent +A @code{filebuf} cannot be in get mode and put mode at the same time. + +We have up to two buffers: + +@itemize @bullet +@item +The backup area, defined by @code{Bbase()}, @code{Bptr()}, and @code{eBptr()}. +This can be empty. + +@item +The reserve area, which also contains the main get area. +For an unbuffered file, the (@code{shortbuf()}..@code{shortbuf()+1}) is used, +where @code{shortbuf()} points to a 1-byte buffer that is part of +the @code{filebuf}. +@end itemize + +@noindent +The file system's idea of the current position is @code{eGptr()}. + +Characters that have been written into a buffer but not yet written +out (flushed) to the file systems are those between @code{pbase()} +and @code{pptr()}. + +The end of the valid data bytes is: +@code{pptr() > eGptr() && pptr() < ebuf() ? pptr() : eGptr()}. + +If the @code{filebuf} is unbuffered or line buffered, +the @code{eptr()} is @code{pbase()}. This forces a call +to @code{overflow()} on each put of a character. +The logical @code{epptr()} is @code{epptr() ? ebuf() : NULL}. +(If the buffer is read-only, set @code{pbase()}, @code{pptr()}, +and @code{epptr()} to @code{NULL}. NOT!) +@end ignore + +@node Index +@unnumbered Index +@printindex cp + +@contents +@bye |