libio Version 0.64bothner@cygnus.com
Cygnus Support doc@cygnus.com
Copyright (C) 1993 Free Software Foundation, Inc.
libio includes software developed by the University of
California, Berkeley.
libio uses floating-point software written by David M. Gay, which
includes the following notice:
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.
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.
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++.
libio
Since the 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 libio.a:
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.
The code is under the 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 libg++
library; if you link with that library instead of libio, the
GNU Library General Public License applies.
Per Bothner wrote most of the 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 libio library. An early
version was originally distributed in libg++, and they are still
included there as well, for convenience if you need other libg++
classes. Doug Lea was the original author of libg++, and some of
the file-management code still in 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.
The GNU iostream library, `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 `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: << for output, and >> 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:
stdout.
stdin.
stderr.
For example, this bare-bones C++ version of the traditional "hello"
program uses << and cout:
#include <iostream.h>
int main(int argc, char **argv)
{
cout << "Well, hi there.\n";
return 0;
}
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 good).
See section Checking the state of a stream. You may also need to
adjust maximum input or output field widths, using manipulators like
setw or setprecision.
ostream.
Defined by this library on any 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 *this (the open stream it
writes on), permitting statements like
cout << "The value of i is " << i << "\n";
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 *this (the open stream
it reads), permitting multiple inputs in one statement.
The previous chapter referred in passing to the classes ostream
and istream, for output and input respectively. These classes
share certain properties, captured in their base class ios.
ios
The base class ios provides methods to test and manage the state
of input or output streams.
ios delegates the job of actually reading and writing bytes to
the abstract class streambuf, which is designed to provide
buffered streams (compatible with C, in the GNU implementation).
See section Using the streambuf Layer, for information on
the facilities available at the streambuf level.
ios constructor by default initializes a new ios, and
if you supply a streambuf sb to associate with it, sets the
state good in the new ios object. It also sets the
default properties of the new object.
You can also supply an optional second argument tie to the
constructor: if present, it is an initial value for ios::tie, to
associate the new ios object with another stream.
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.
Use this collection of methods to test for (or signal) errors and other exceptional conditions of streams:
ios::fail is not true). For example, you might ask for
input on cin only if all prior output operations succeeded:
if (cout)
{
// Everything OK so far
cin >> new_value;
...
}
! returns true if ios::fail is true (an operation
has failed). For example,
you might issue an error message if input failed:
if (!cin)
{
// Oops
cerr << "Eh?\n";
}
iostate. You can test for any combination of
goodbit
eofbit
failbit
badbit
ios::set.
See ios::clear to set the stream state without regard to existing
state flags. See ios::good, ios::eof, ios::fail,
and ios::bad, to test the state.
ios::badbit is set.)
ios::eofbit
is set.)
ios::failbit or ios::badbit is set.)
ios::clear with no argument, in which case the state
is set to good (no errors pending).
See ios::good, ios::eof, ios::fail, and
ios::bad, to test the state; see ios::set or
ios::setstate for an alternative way of setting the state.
These methods control (or report on) settings for some details of controlling streams, primarily to do with formatting output:
setfill. See section Changing stream properties using manipulators.
Default: blank.
Default: 6.
You can also use the manipulator setprecision for this purpose.
See section Changing stream properties using manipulators.
Default: 0, which means to use as many characters as necessary.
This value resets to zero (the default) every time you use `<<'; it is
essentially an additional implicit argument to that operator. You can
also use the manipulator setw for this purpose.
See section Changing stream properties using manipulators.
ios::dec
ios::oct
ios::hex
setbase, or any of the manipulators dec, oct, or
hex; see section Changing stream properties using manipulators.)
On input, if none of these flags is set, read numeric constants
according to the prefix: decimal if no prefix (or a `.' suffix),
octal if a `0' prefix is present, hexadecimal if a `0x' prefix
is present.
Default: dec.
ios::fixed
ios::precision to set precision.
ios::left
ios::right
ios::internal
ios::scientific
ios::showbase
ios::showpoint
ios::showpos
ios::skipws
ios::stdio
stdio streams stdout and stderr after
each output operation (for programs that mix C and C++ output conventions).
ios::unitbuf
ios::uppercase
Use ios::setf or ios::unsetf to change one property at a
time.
ios::unsetf to cancel.)
ios::unsetf for another way of clearing flags.)
ios::setf. Returns the old values of those flags.
For convenience, manipulators provide a way to change certain properties of streams, or otherwise affect them, in the middle of expressions involving `<<' or `>>'. For example, you might write
cout << "|" << setfill('*') << setw(5) << 234 << "|";
to produce `|**234|' as output.
ios::precision in `<<'
expressions with the manipulator `setprecision(signif)'; for
example,
cout << setprecision(2) << 4.567;
prints `4.6'. Requires `#include <iomanip.h>'.
ios::width in `<<' expressions
with the manipulator `setw(n)'; for example,
cout << setw(5) << 234;
prints ` 234' with two leading blanks. Requires `#include <iomanip.h>'.
10 (decimal), 8 (octal), or
16 (hexadecimal), change the base value for numeric
representations. Requires `#include <iomanip.h>'.
ios::fill.
Requires `#include <iomanip.h>'.
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:
bitalloc guards against conflict between two packages that use
ios objects for different purposes.
This method is available for upward compatibility, but is not in the
ANSI working paper. The number of bits available is limited; a
return value of 0 means no bit is available.
ios::iword or ios::pword. Use xalloc to arrange
for arbitrary special-purpose data in your ios objects, without
risk of conflict between packages designed for different purposes.
ios instance. index, conventionally returned from
ios::xalloc, identifies what particular data you need.
ios.
ios
instance. index, originally returned from ios::xalloc,
identifies what particular pointer you need.
ios.
You can use these methods to synchronize related streams with one another:
0 means no stream is tied.
stdio are designed to work together, you
may have to choose between efficient C++ streams output and output
compatible with C stdio. Use `ios::sync_with_stdio()' to
select C compatibility.
The argument switch is a GNU extension; use 0 as the
argument to choose output that is not necessarily compatible with C
stdio. The default value for switch is 1.
If you install the stdio implementation that comes with GNU
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.
streambufFinally, you can use this method to access the underlying object:
streambuf object that underlies this
ios.
ostream
Objects of class ostream inherit the generic methods from
ios, and in addition have the following methods available.
Declarations for this class come from `iostream.h'.
ostream simply
allocates a new ios object.
streambuf*, to use an existing open stream for output. It also
accepts an optional second argument tie, to specify a related
ostream* as the initial value for ios::tie.
If you give the ostream a streambuf explicitly, using
this constructor, the sb is not destroyed (or deleted or
closed) when the ostream is destroyed.
ostream
These methods write on an ostream (you may also use the operator
<<; see section Operators and Default Streams).
ostream,
beginning at the pointer string.
string may have any of these types: char*, unsigned
char*, signed char*.
fprintf(file,
format, ...).
format is a printf-style format control string, which is used
to format the (variable number of) arguments, printing the result on
this ostream. See ostream::vform for a version that uses
an argument list rather than a variable number of arguments.
vfprintf(file,
format, args).
format is a printf-style format control string, which is used
to format the argument list args, printing the result on
this ostream. See ostream::form for a version that uses a
variable number of arguments rather than an argument list.
ostreamYou can control the output position (on output streams that actually support positions, typically files) with these methods:
ostream::tellp). loc specifies an
absolute position in the output stream.
ios::seekdir):
beg
cur
end
ostream utilities
You may need to use these ostream methods for housekeeping:
ostream.
opfx is a prefix method for operations on ostream
objects; it is designed to be called before any further processing. See
ostream::osfx for the converse.
opfx tests that the stream is in state good, and if so
flushes any stream tied to this one.
The result is 1 when opfx succeeds; else (if the stream state is
not good), the result is 0.
osfx is a suffix method for operations on ostream
objects; it is designed to be called at the conclusion of any processing. All
the ostream methods end by calling osfx. See
ostream::opfx for the converse.
If the unitbuf flag is set for this stream, osfx flushes
any buffered output for it.
If the stdio flag is set for this stream, osfx flushes any
output buffered for the C output streams `stdout' and `stderr'.
istream
Class istream objects are specialized for input; as for
ostream, they are derived from ios, so you can use any of
the general-purpose methods from that base class. Declarations for this
class also come from `iostream.h'.
istream constructor simply
allocates a new ios object and initializes the input counter (the
value reported by istream::gcount) to 0.
streambuf*; if you supply this pointer,
the constructor uses that streambuf for input.
You can use the second optional argument tie to specify a related
output stream as the initial value for ios::tie.
If you give the istream a streambuf explicitly, using
this constructor, the sb is not destroyed (or deleted or
closed) when the ostream is destroyed.
Use these methods to read a single character from the input stream:
EOF) from the input stream, returning
it (coerced to an unsigned char) as the result.
&c.
Use these methods to read strings (for example, a line at a time) from the input stream:
The remaining arguments limit how much to read: up to `len-1'
characters, or up to (but not including) the first occurrence in the
input of a particular delimiter character delim---newline
(\n) by default. (Naturally, if the stream reaches end of file
first, that too will terminate reading.)
If delim was present in the input, it remains available as if
unread; to discard it instead, see iostream::getline.
get writes `\0' at the end of the string, regardless
of which condition terminates the read.
streambuf object sb. Copying ends either just before the
next instance of the delimiter character delim (newline \n
by default), or when either stream ends. If delim was present in
the input, it remains available as if unread.
char*,
unsigned char*, or 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 delim---newline (\n) by default, or up to
`len-1' characters (or to end of file, if that happens sooner).
If 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 iostream::get.)
If delim was not found before len characters or end
of file, getline sets the ios::fail flag, as well as the
ios::eof flag if appropriate.
getline writes a null character at the end of the string, regardless
of which condition terminates the read.
pointer may be of type char*, void*, unsigned
char*, or signed char*.
If the istream ends before reading len bytes, read
sets the ios::fail flag.
\n by default).
To permit reading a string of arbitrary length, gets allocates
whatever memory is required. Notice that the first argument s is
an address to record a character pointer, rather than the pointer
itself.
fscanf(file,
format, ...). The format is a scanf-style format
control string, which is used to read the variables in the remainder of
the argument list from the istream.
istream::scan, but takes a single va_list argument.
istreamUse these methods to control the current input position:
istream::seekg.
istream::tellg.
ios::beg
ios::cur
ios::end
istream utilities
Use these methods for housekeeping on istream objects:
istream in the
last unformatted input operation.
istream object is ready for reading; check for
errors and end of file and flush any tied stream. ipfx skips
whitespace if you specify 0 as the keepwhite
argument, and ios::skipws is set for this stream.
To avoid skipping whitespace (regardless of the skipws setting on
the stream), use 1 as the argument.
Call istream::ipfx to simplify writing your own methods for reading
istream objects.
If you wish to write portable standard-conforming code on istream
objects, call isfx after any operation that reads from an
istream; if istream::ipfx has any special effects that
must be cancelled when done, istream::isfx will cancel them.
ignore returns immediately if this character appears in the
input.
By default, delim is EOF; that is, if you do not specify a
second argument, only the count n restricts how much to ignore
(while input is still available).
If you do not specify how many characters to ignore, ignore
returns after discarding only one character.
EOF if this is not allowed. Putting
back the most recently read character is always allowed. (This method
corresponds to the C function ungetc.)
iostream
If you need to use the same stream for input and output, you can use an
object of the class iostream, which is derived from both
istream and ostream.
The constructors for iostream behave just like the constructors
for istream.
iostream constructor simply
allocates a new ios object, and initializes the input counter
(the value reported by istream::gcount) to 0.
streambuf*; if you supply this pointer,
the constructor uses that streambuf for input and output.
You can use the optional second argument tie (an ostream*)
to specify a related output stream as the initial value for
ios::tie.
As for ostream and istream, iostream simply uses
the ios destructor. However, an iostream is not deleted by
its destructor.
You can use all the istream, ostream, and ios
methods with an iostream object.
There are two very common special cases of input and output: using files, and using strings in memory.
libio defines four specialized classes for these cases:
ifstream
ofstream
istrstream
ostrstream
These methods are declared in `fstream.h'.
You can read data from class ifstream with any operation from class
istream. There are also a few specialized facilities:
ifstream associated with a new file for input. (If you
use this version of the constructor, you need to call
ifstream::open before actually reading anything)
ifstream for reading from a file that was already open,
using file descriptor fd. (This constructor is compatible with
other versions of iostreams for POSIX systems, but is not part of
the ANSI working paper.)
*fname for this ifstream object.
By default, the file is opened for input (with ios::in as
mode). If you use this constructor, the file will be closed when
the ifstream is destroyed.
You can use the optional argument mode to specify how to open the
file, by combining these enumerated values (with `|' bitwise or).
(These values are actually defined in class ios, so that all
file-related streams may inherit them.) Only some of these modes are
defined in the latest draft ANSI specification; if portability is
important, you may wish to avoid the others.
ios::in
ios::out
ios::ate
ios::app
ios::trunc
ios::nocreate
ios::noreplace
ios::bin
The last optional argument prot is specific to Unix-like systems; it specifies the file protection (by default `644').
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 ifstream constructor.
You can write data to class ofstream with any operation from class
ostream. There are also a few specialized facilities:
ofstream associated with a new file for output.
ofstream for writing to a file that was already open,
using file descriptor fd.
*fname for this ofstream object.
By default, the file is opened for output (with ios::out as mode).
You can use the optional argument mode to specify how to open the
file, just as described for ifstream::ifstream.
The last optional argument prot specifies the file protection (by default `644').
ofstream objects are closed when the
corresponding object is destroyed.
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 ofstream constructor.
The class fstream combines the facilities of ifstream and
ofstream, just as iostream combines istream and
ostream.
The class fstreambase underlies both ifstream and
ofstream. They both inherit this additional method:
ios::fail in
this object to mark the event.
The classes istrstream, ostrstream, and strstream
provide some additional features for reading and writing strings in
memory--both static strings, and dynamically allocated strings. The
underlying class strstreambase provides some features common to
all three; strstreambuf underlies that in turn.
istrstream with an existing
static string starting at str, of size size. If you do not
specify size, the string is treated as a NUL terminated string.
ifstream::ifstream; if you do not specify
one, the new stream is simply open for output, with mode ios::out.
ostrstream.
ostrstream. Implies
`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).
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 ostrstream is destroyed. Use
`freeze(1)' if you refer to the string as a pointer after creating
it via ostrstream facilities.
`freeze(0)' cancels this declaration, allowing a dynamically
allocated string to be freed when its ostrstream is destroyed.
If this ostrstream is already static--that is, if it was created
to manage an existing statically allocated string---freeze is
unnecessary, and has no effect.
freeze(1) is in effect for this string.
strstreambuf.
streambuf Layer
The istream and ostream classes are meant to handle
conversion between objects in your program and their textual representation.
By contrast, the underlying streambuf class is for transferring
raw bytes between your program, and input sources or output sinks.
Different streambuf subclasses connect to different kinds of
sources and sinks.
The GNU implementation of streambuf is still evolving; we
describe only some of the highlights.
streambufStreambuf buffer management is fairly sophisticated (this is a nice way to say "complicated"). The standard protocol has the following "areas":
The GNU 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 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.)
pptr() < epptr (), the pptr()
returns a pointer to the current put position.
(In that case, the next write will
overwrite *pptr(), and increment pptr().)
Otherwise, there is no put position available
(and the next character written will cause streambuf::overflow
to be called).
gptr() < egptr (), then gptr()
returns a pointer to the current get position.
(In that case the next read will read *gptr(),
and possibly increment gptr().)
Otherwise, there is no read position available
(and the next read will cause streambuf::underflow
to be called).
overflow
Suppose you have a function write_to_window that
writes characters to a 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).
#include <iostream.h>
/* Returns number of characters successfully written to 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";
}
streambuf objects
The GNU streambuf class supports printf-like
formatting and scanning.
fprintf(file, format, ...).
The format is a printf-style format control string, which is used
to format the (variable number of) arguments, printing the result on
the this streambuf. The result is the number of characters printed.
vfprintf(file, format, args).
The format is a printf-style format control string, which is used
to format the argument list args, printing the result on
the this streambuf. The result is the number of characters printed.
fscanf(file, format, ...).
The format is a scanf-style format control string, which is used
to read the (variable number of) arguments from the this streambuf.
The result is the number of items assigned, or EOF in case of
input failure before any conversion.
streambuf::scan, but takes a single va_list argument.
stdio
A stdiobuf is a streambuf object that points to
a FILE object (as defined by stdio.h).
All streambuf operations on the stdiobuf are forwarded
to the FILE. Thus the stdiobuf object provides a
wrapper around a FILE, allowing use of streambuf
operations on a FILE. This can be useful when mixing
C code with C++ code.
The pre-defined streams cin, cout, and cerr are
normally implemented as stdiobuf objects that point to
respectively stdin, stdout, and stderr. This is
convenient, but it does cost some extra overhead.
If you set things up to use the implementation of stdio provided
with this library, then cin, cout, and cerr will be
set up to to use stdiobuf objects, since you get their benefits
for free. See section C Input and Output.
The procbuf class is a GNU extension. It is derived from
streambuf. A procbuf can be closed (in which case
it does nothing), or open (in which case it allows communicating
through a pipe with some other program).
procbuf in a closed state.
If mode is `ios::in', standard output from the program is sent
to a pipe; you can read from the pipe by reading from the
procbuf. (This is similar to `popen(command, "r")'.)
If mode is `ios::out', output written written to the
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
`popen(command, "w")'.)
The procbuf must start out in the closed state.
Returns `*this' on success, and `NULL' on failure.
The GNU iostream library allows you to ask a 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:
// 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;
}
streammarker associated with sbuf
that remembers the current position of the get pointer.
*this and mark2 (which must point into the same
streambuffer as this).
An indirectbuf is one that forwards all of its I/O requests to another streambuf.
An indirectbuf can be used to implement Common Lisp
synonym-streams and two-way-streams:
class synonymbuf : public indirectbuf {
Symbol *sym;
synonymbuf(Symbol *s) { sym = s; }
virtual streambuf *lookup_stream(int mode) {
return coerce_to_streambuf(lookup_value(sym)); }
};
libio is distributed with a complete implementation of the ANSI C
stdio facility. It is implemented using streambuf
objects. See section Wrappers for C stdio.
The stdio package is intended as a replacement for the whatever
stdio is in your C library.
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:
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.
FILE from C. Thus the system is extensible using the standard
streambuf protocol.
ungetc() buffer.
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ios::precision
ios::width
This document was generated on 3 March 1999 using the texi2html translator version 1.52.