FSTREAM(3C++) FSTREAM(3C++)
NAMEfstream - iostream and streambuf specialized to files
SYNOPSIS
#include <fstream.h>
typedef long streamoff, streampos;
class ios {
public:
enum seek_dir { beg, cur, end } ;
enum open_mode { in, out, ate, app, trunc, nocreate, noreplace } ;
enum io_state { goodbit=0, eofbit, failbit, badbit } ;
// and lots of other stuff, see ios(3C++) ...
} ;
class ifstream : istream {
ifstream() ;
~ifstream() ;
ifstream(const char* name, int =ios::in,
int prot =filebuf::openprot) ;
ifstream(int fd) ;
ifstream(int fd, char* p, int l) ;
void attach(int fd) ;
void close() ;
void open(char* name, int =ios::in,
int prot=filebuf::openprot) ;
filebuf* rdbuf() ;
void setbuf(char* p, int l) ;
};
class ofstream : ostream {
ofstream() ;
~ofstream() ;
ofstream(const char* name, int =ios::out,
int prot =filebuf::openprot) ;
ofstream(int fd) ;
ofstream(int fd, char* p, int l) ;
void attach(int fd) ;
void close() ;
void open(char* name, int =ios::out, int prot=filebuf::openprot) ;
filebuf* rdbuf() ;
void setbuf(char* p, int l) ;
};
class fstream : iostream {
fstream() ;
~fstream() ;
fstream(const char* name, int mode,
int prot =filebuf::openprot) ;
fstream(int fd) ;
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FSTREAM(3C++) FSTREAM(3C++)
fstream(int fd, char* p, int l) ;
void attach(int fd) ;
void close() ;
void open(char* name, int mode, int prot=filebuf::openprot) ;
filebuf* rdbuf() ;
void setbuf(char* p, int l) ;
};
DESCRIPTION
ifstream, ofstream, and fstream specialize istream, ostream, and
iostream, respectively, to files. That is, the associated streambuf will
be a filebuf.
In the following descriptions, assume
- f is any of ifstream, ofstream, or fstream.
- pfb is a filebuf*.
- psb is a streambuf*.
- name and ptr are char*s.
- i, fd, len, and prot are ints.
- mode is an int representing an open_mode.
Constructors
The constructors for xstream, where x is either if, of, or f, are:
xstream()
Constructs an unopened xstream.
xstream(name, mode, prot)
Constructs an xstream and opens file name using mode as the
open mode and prot as the protection mode. By default, prot is
filebuf::openprot, which is 0644. The error state (io_state)
of the constructed xstream will indicate failure in case the
open fails.
xstream(d)
Constructs an xstream connected to file descriptor d, which
must be already open.
xstream(d,ptr,len)
Constructs an xstream connected to file descriptor d, and, in
addition, initializes the associated filebuf to use the len
bytes at ptr as the reserve area. If ptr is null or len is 0,
the filebuf will be unbuffered.
Member functions
f.attach(d)
Connects f to the file descriptor d. A failure occurs when f
is already connected to a file. A failure sets ios::failbit in
f's error state.
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FSTREAM(3C++) FSTREAM(3C++)
f.close()
Closes any associated filebuf and thereby breaks the connection
of the f to a file. f's error state is cleared except on
failure. A failure occurs when the call to f.rdbuf()->close()
fails.
f.open(name,mode,prot)
Opens file name and connects f to it. If the file does not
already exist, an attempt is made to create it with protection
mode prot unless ios::nocreate is set. By default, prot is
filebuf::openprot, which is 0644. Failure occurs if f is
already open, or the call to f.rdbuf()->open() fails.
ios::failbit is set in f's error status on failure. The
members of open_mode are bits that may be or'ed together.
(Because the or'ing returns an int, open() takes an int rather
than an open_mode argument.) The meanings of these bits in
mode are:
ios::app
A seek to the end of file is performed. Subsequent data
written to the file is always added (appended) at the end
of file. On some systems this is implemented in the
operating system. In others it is implemented by seeking
to the end of the file before each write. ios::app
implies ios::out.
ios::ate
A seek to the end of the file is performed during the
open(). ios::ate does not imply ios::out.
ios::in
The file is opened for input. ios::in is implied by
construction and opens of ifstreams. For fstreams it
indicates that input operations should be allowed if
possible. Is is legal to include ios::in in the modes of
an ostream in which case it implies that the original file
(if it exists) should not be truncated. If the file being
opened for input does not exist, the open will fail.
ios::out
The file is opened for output. ios::out is implied by
construction and opens of ofstreams. For fstream it says
that output operations are to be allowed. ios::out may be
specified even if prot does not permit output.
ios::trunc
If the file already exists, its contents will be truncated
(discarded). This mode is implied when ios::out is
specified (including implicit specification for ofstream)
and neither ios::ate nor ios::app is specified.
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FSTREAM(3C++) FSTREAM(3C++)
ios::nocreate
If the file does not already exist, the open() will fail.
ios::noreplace
If the file already exists, the open() will fail. Only
valid with ios::out.
pfb=f.rdbuf()
Returns a pointer to the filebuf associated with f.
fstream::rdbuf() has the same meaning as iostream::rdbuf() but
is typed differently.
f.setbuf(p,len)
Has the usual effect of a setbuf() (see filebuf(3C++)),
offering space for a reserve area or requesting unbuffered I/O.
Normally the returned psb is f.rdbuf(), but it is 0 on failure.
A failure occurs if f is open or the call to f.rdbuf()->setbuf
fails.
SEE ALSO
filebuf(3C++), istream(3C++), ios(3C++), ostream(3C++), sbuf.pub(3C++)
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