ifstream::ifstream

ifstream();

ifstream( const char* szName, int nMode = ios::in, int nProt = filebuf::openprot );

ifstream( filedesc fd );

ifstream( filedesc fd, char* pch, int nLength );

Parameters

szName

The name of the file to be opened during construction.

nMode

An integer that contains mode bits defined as ios enumerators that can be combined with the bitwise OR ( | ) operator. The nMode parameter must have one of the following values:

• ios::in   The file is opened for input (default).
  
  
• ios::nocreate   If the file does not already exist, the function fails.
  
  
• ios::binary   Opens the file in binary mode (the default is text mode).

  Note that the ios::nocreate flag is necessary if you intend to test for the file’s existence (the usual case).

nProt

The file protection specification; defaults to the static integer filebuf::openprot that is equivalent to filebuf::sh_compat. The possible nProt values are:

• filebuf::sh_compat   Compatibility share mode.
  
  
• filebuf::sh_none   Exclusive mode — no sharing.
  
  
• filebuf::sh_read   Read sharing allowed.
  
  
• filebuf::sh_write   Write sharing allowed.

  To combine the filebuf::sh_read and filebuf::sh_write modes, use the logical OR ( || ) operator.

fd

A file descriptor as returned by a call to the run-time function _open or _sopen; filedesc is a typedef equivalent to int.

pch

Pointer to a previously allocated reserve area of length nLength. A NULL value (or nLength = 0) indicates that the stream will be unbuffered.

nLength

The length (in bytes) of the reserve area (0 = unbuffered).

Remarks

The four ifstream constructors are:

• ifstream()   Constructs an ifstream object without opening a file.
  
  
• ifstream( const char*, int, int )   Contructs an ifstream object, opening the specified file.
  
  
• ifstream( filedesc )   Constructs an ifstream object that is attached to an open file.
  
  
• ifstream( filedesc, char*, int )   Constructs an ifstream object that is associated with a filebuf object. The filebuf object is attached to an open file and to a specified reserve area.

All ifstream constructors construct a filebuf object. The first three use an internally allocated reserve area, but the fourth uses a user-allocated area.

ifstream Overview |  Input Stream Classes