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Synopsis:
    #include <sys\types.h>
    #include <sys\stat.h>
    #include <fcntl.h>
    int open( const char *path, int access, ... );
    int _open( const char *path, int access, ... );
    int _wopen( const wchar_t *path, int access, ... );

Description:
    The open function opens a file at the operating system level.  The name
    of the file to be opened is given by path.  The file will be accessed
    according to the access mode specified by access.  The optional argument
    is the file permissions to be used when the  O_CREAT flag is on in the
    access mode.

    The _open function is identical to open.  Use _open for ANSI/ISO naming
    conventions.

    The _wopen function is identical to open except that it accepts a wide
    character string argument for path.

    The access mode is established by a combination of the bits defined in
    the <fcntl.h> header file.  The following bits may be set:

    Mode     Meaning

O_RDONLY
    permit the file to be only read.

O_WRONLY
    permit the file to be only written.

O_RDWR
    permit the file to be both read and written.

O_APPEND
    causes each record that is written to be written at the end of the file.

O_CREAT
    has no effect when the file indicated by filename already exists;
    otherwise, the file is created;

O_TRUNC
    causes the file to be truncated to contain no data when the file exists;
    has no effect when the file does not exist.

O_BINARY
    causes the file to be opened in binary mode which means that data will
    be transmitted to and from the file unchanged.

O_TEXT
    causes the file to be opened in text mode which means that
    carriage-return characters are written before any linefeed character
    that is written and causes carriage-return characters to be removed when
    encountered during reads.

O_NOINHERIT
    indicates that this file is not to be inherited by a child process.

O_EXCL
    indicates that this file is to be opened for exclusive access.  If the
    file exists and  O_CREAT was also specified then the open will fail
    (i.e., use  O_EXCL to ensure that the file does not already exist).

    When neither  O_TEXT nor  O_BINARY are specified, the default value in
    the global variable  _fmode is used to set the file translation mode.
     When the program begins execution, this variable has a value of
     O_TEXT.

     O_CREAT must be specified when the file does not exist and it is to be
    written.

    When the file is to be created ( O_CREAT is specified), an additional
    argument must be passed which contains the file permissions to be used
    for the new file.  The access permissions for the file or directory are
    specified as a combination of bits (defined in the <sys\stat.h> header
    file).

    The following bits define permissions for the owner.

    Permission     Meaning

S_IRWXU
    Read, write, execute/search

S_IRUSR
    Read permission

S_IWUSR
    Write permission

S_IXUSR
    Execute/search permission

    The following bits define permissions for the group.

    Permission     Meaning

S_IRWXG
    Read, write, execute/search

S_IRGRP
    Read permission

S_IWGRP
    Write permission

S_IXGRP
    Execute/search permission

    The following bits define permissions for others.

    Permission     Meaning

S_IRWXO
    Read, write, execute/search

S_IROTH
    Read permission

S_IWOTH
    Write permission

S_IXOTH
    Execute/search permission

    The following bits define miscellaneous permissions used by other
    implementations.

    Permission     Meaning

S_IREAD
    is equivalent to S_IRUSR (read permission)

S_IWRITE
    is equivalent to S_IWUSR (write permission)

S_IEXEC
    is equivalent to S_IXUSR (execute/search permission)

    All files are readable with DOS; however, it is a good idea to set
     S_IREAD when read permission is intended for the file.

    The open function applies the current file permission mask to the
    specified permissions (see  umask).

Returns:
    If successful, open returns a handle for the file.  When an error occurs
    while opening the file, -1 is returned.

Errors:
    When an error has occurred,  errno contains a value indicating the type
    of error that has been detected.

    Constant     Meaning

EACCES
    Access denied because path specifies a directory or a volume ID, or
    attempting to open a read-only file for writing

EMFILE
    No more handles available (too many open files)

ENOENT
    Path or file not found


Example:
    #include <sys\stat.h>
    #include <sys\types.h>
    #include <fcntl.h>

    void main()
      {
        int handle;
        /* open a file for output                  */
        /* replace existing file if it exists      */

        handle = open( "file",
                    O_WRONLY | O_CREAT | O_TRUNC,
                    S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP );

        /* read a file which is assumed to exist   */

        handle = open( "file", O_RDONLY );

        /* append to the end of an existing file   */
        /* write a new file if file does not exist */

        handle = open( "file",
                    O_WRONLY | O_CREAT | O_APPEND,
                    S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP );
      }

Classification:
    open is POSIX 1003.1, _open is not POSIX, _wopen is not POSIX

_open conforms to ANSI/ISO naming conventions

Systems:
     open - All, Netware

    _open - DOS, Windows, Win386, Win32, OS/2 1.x(all), OS/2-32
    _wopen - DOS, Windows, Win386, Win32, OS/2 1.x(all), OS/2-32

See Also:
    chsize, close, creat, dup, dup2, eof, exec Functions, filelength,
    fileno, fstat, isatty, lseek, read, setmode, sopen, stat, tell, write,
    umask