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(iostream-295.info)Files

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Enter node , (file) or (file)node

Reading and writing files
=========================

   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:

 - Constructor:  ifstream::ifstream ()
     Make an `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)

 - Constructor:  ifstream::ifstream (int FD)
     Make an `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.)

 - Constructor:  ifstream::ifstream (const char* FNAME [, int MODE
          [, int PROT]])
     Open a file `*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'
          Open for input.  (Included in ANSI draft.)

    `ios::out'
          Open for output.  (Included in ANSI draft.)

    `ios::ate'
          Set the initial input (or output) position to the end of the
          file.

    `ios::app'
          Seek to end of file before each write.  (Included in ANSI
          draft.)

    `ios::trunc'
          Guarantee a fresh file; discard any contents that were
          previously associated with it.

    `ios::nocreate'
          Guarantee an existing file; fail if the specified file did
          not already exist.

    `ios::noreplace'
          Guarantee a new file; fail if the specified file already
          existed.

    `ios::bin'
          Open as a binary file (on systems where binary and text files
          have different properties, typically how `\n' is mapped;
          included in ANSI draft).

     The last optional argument PROT is specific to Unix-like systems;
     it specifies the file protection (by default `0644').

 - Method: void ifstream::open (const char* FNAME [, int MODE [, int
          PROT]])
     Open a file explicitly after the associated `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:

 - Constructor:  ofstream::ofstream ()
     Make an `ofstream' associated with a new file for output.

 - Constructor:  ofstream::ofstream (int FD)
     Make an `ofstream' for writing to a file that was already open,
     using file descriptor FD.

 - Constructor:  ofstream::ofstream (const char* FNAME [, int MODE
          [, int PROT]])
     Open a file `*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 `0644').

 - Destructor:  ofstream::~ofstream ()
     The files associated with `ofstream' objects are closed when the
     corresponding object is destroyed.

 - Method: void ofstream::open (const char* FNAME [, int MODE [, int
          PROT]])
     Open a file explicitly after the associated `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:

 - Method: void fstreambase::close ()
     Close the file associated with this object, and set `ios::fail' in
     this object to mark the event.