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VMS Help CXXLSTD, IOStreams, fstream *Conan The Librarian |
Standard C++ Library
Copyright 1996, Rogue Wave Software, Inc.
NAME
basic_fstream,fstream,ofstream
This page describes the ANSI basic_fstream class. If you would like
information on the pre-ANSI fstream class, use the command:
help cxxl
SYNOPSIS
#include <fstream>
template<class charT, class traits = char_traits<charT> >
class basic_fstream
: public basic_iostream<charT, traits>
DESCRIPTION
The template class basic_fstream<charT,traits> supports reading and
writing to named files or other devices associated with a file
descriptor. It uses a basic_filebuf object to control the
associated sequences. It inherits from basic_iostream and can
therefore use all the formatted and unformatted input and
output functions.
INTERFACE
template<class charT, class traits = char_traits<charT> >
class basic_fstream
: public basic_iostream<charT, traits> {
public:
typedef basic_ios<charT, traits> ios_type;
typedef charT char_type;
typedef traits traits_type;
typedef typename traits::int_type int_type;
typedef typename traits::pos_type pos_type;
typedef typename traits::off_type off_type;
basic_fstream();
explicit basic_fstream(const char *s, ios_base::openmode
mode = ios_base::in | ios_base::out,
long protection = 0666);
explicit basic_fstream(int fd);
basic_fstream(int fd, char_type *buf, int len);
virtual ~basic_fstream();
basic_filebuf<charT, traits> *rdbuf() const;
bool is_open();
void open(const char *s, ios_base::openmode mode =
ios_base::in | ios_base::out,
long protection = 0666);
void close();
};
TYPES
char_type
The type char_type is a synonym for the template parameter charT.
fstream
The type fstream is an instantiation of class basic_fstream on type
char:
typedef basic_fstream<char> fstream;
int_type
The type int_type is a synonym of type traits::in_type.
ios_type
The type ios_type is an instantiation of class basic_ios on type
charT.
off_type
The type off_type is a synonym of type traits::off_type.
pos_type
The type pos_type is a synonym of type traits::pos_type.
traits_type
The type traits_type is a synonym for the template parameter
traits.
wfstream
The type wfstream is an instantiation of class basic_fstream on
type wchar_t:
typedef basic_fstream<wchar_t> wfstream;
CONSTRUCTORS
basic_fstream();
Constructs an object of class basic_fstream<charT,traits>,
initializing the base class basic_iostream with the associated
file buffer, which is initialized by calling the basic_filebuf
constructor basic_filebuf<charT,traits>(). After construction,
a file can be attached to the basic_ftream object by using the
open() member function.
basic_fstream(const char* s,
ios_base::openmode mode=
ios_base::in | iosw_base::out,
long protection= 0666);
Constructs an object of class basic_fstream<charT,traits>,
initializing the base class basic_iostream with the associ-
ated file buffer, which is initialized by calling the
basic_filebuf constructor basic_filebuf<charT,traits>().
The constructor then calls the open function
open(s,mode,protection) in order to attach the file, whose
name is pointed at by s, to the basic_ftream object. The
third argument, protection, is used as the file permission.
It does not appear in the Standard C++ description and is
provided as an extension. It determines the file
read/write/execute permissions under UNIX. It is more lim-
ited under DOS since files are always readable and do not
have special execute permission.
explicit basic_fstream(int fd);
Constructs an object of class basic_fstream<charT,traits>,
initializing the base class basic_iostream with the associated
file buffer, which is initialized by calling the basic_filebuf
constructor basic_filebuf<charT,traits>(). The constructor
then calls the basic_filebuf open function open(fd) in order to
attach the file descriptor fd to the basic_ftream object. This
constructor is not described in the C++ standard, and
is provided as an extension in order to manipulate pipes,
sockets or other UNIX devices, that can be accessed through
file descriptors. If the function fails, it sets
ios_base::failbit.
basic_fstream(int fd, char_type* buf,int len);
Constructs an object of class basic_fstream<charT,traits>,
initializing the base class basic_iostream with the associated
file buffer, which is initialized by calling the basic_filebuf
constructor basic_filebuf<charT,traits>(). The constructor
then calls the basic_filebuf open function open(fd) in order to
attach the file descriptor fd to the basic_ftream object. The
underlying buffer is then replaced by calling the
basic_filebuf member function, setbuf(), with parameters buf
and len. This constructor is not described in the C++
standard, and is provided as an extension in order to manipulate
pipes, sockets, or other UNIX devices that can be accessed
through file descriptors. It also maintains compatibility with
the old iostreams library. If the function fails, it sets
ios_base::failbit.
DESTRUCTOR
virtual ~basic_fstream();
Destroys an object of class basic_fstream.
MEMBER FUNCTIONS
void
close();
Calls the associated basic_filebuf function close() and if this
function fails, it calls the basic_ios member function
setstate(failbit).
bool
is_open();
Calls the associated basic_filebuf function is_open() and return
its result.
void
open(const char* s,ios_base::openmode =
ios_base::out | ios_base::in,
long protection = 0666);
Calls the associated basic_filebuf function open(s,mode,protection)
and, if this function fails at opening the file, calls the basic_ios
member function setstate(failbit). The third argument protection is
used as the file permissions. It does not appear in the Standard C++
description and is provided as an extension. It determines the file
read/write/execute permissions under UNIX. It is more limited under
DOS since files are always readable and do not have special execute
permission.
basic_filebuf<charT,traits>*
rdbuf() const;
Returns a pointer to the basic_filebuf associated with the stream.
EXAMPLES
//
// stdlib/examples/manual/fstream.cpp
//
#include<iostream>
#include<bidirec>
void main ( )
{
using namespace std;
// create a bi-directional fstream object
fstream inout("fstream.out");
// output characters
inout << "Das ist die rede von einem man" << endl;
inout << "C'est l'histoire d'un home" << endl;
inout << "This is the story of a man" << endl;
char p[100];
// seek back to the beginning of the file
inout.seekg(0);
// extract the first line
inout.getline(p,100);
// output the first line to stdout
cout << endl << "Deutch :" << endl;
cout << p;
fstream::pos_type pos = inout.tellg();
// extract the seconf line
inout.getline(p,100);
// output the second line to stdout
cout << endl << "Francais :" << endl;
cout << p;
// extract the third line
inout.getline(p,100);
// output the third line to stdout
cout << endl << "English :" << endl;
cout << p;
// move the put sequence before the second line
inout.seekp(pos);
// replace the second line
inout << "This is the story of a man" << endl;
// replace the third line
inout << "C'est l'histoire d'un home";
// seek to the beginning of the file
inout.seekg(0);
// output the all content of the fstream object to stdout
cout << endl << endl << inout.rdbuf();
}
SEE ALSO
char_traits, ios_base, basic_ios,
basic_filebuf, basic_ifstream, basic_ofstream
Working Paper for Draft Proposed International Standard for Information
Systems--Programming Language C++, Section 27.8.1.11
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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