_sopen, _wsopen

Open a file for sharing.

int _sopen( const char *filename, int oflag, int shflag [, int pmode ] );

int _wsopen( const wchar_t *filename, int oflag, int shflag [, int pmode ] );

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

Each of these functions returns a file handle for the opened file. A return value of –1 indicates an error, in which case errno is set to one of the following values:

EACCES

Given path is a directory, or file is read-only, but an open-for-writing operation was attempted.

EEXIST

_O_CREAT and _O_EXCL flags were specified, but filename already exists.

EINVAL

Invalid oflag or shflag argument.

EMFILE

No more file handles available.

ENOENT

File or path not found.

Parameters

filename

Filename

oflag

Type of operations allowed

shflag

Type of sharing allowed

pmode

Permission setting

Remarks

The _sopen function opens the file specified by filename and prepares the file for shared reading or writing, as defined by oflag and shflag. _wsopen is a wide-character version of _sopen; the filename argument to _wsopen is a wide-character string. _wsopen and _sopen behave identically otherwise.

Generic-Text Routine Mappings

The integer expression oflag is formed by combining one or more of the following manifest constants, defined in the file FCNTL.H. When two or more constants form the argument oflag, they are combined with the bitwise-OR operator ( | ).

_O_APPEND

Repositions file pointer to end of file before every write operation.

_O_BINARY

Opens file in binary (untranslated) mode. (See fopen for a description of binary mode.)

_O_CREAT

Creates and opens new file for writing. Has no effect if file specified by filename exists. The pmode argument is required when _O_CREAT is specified.

_O_CREAT | _O_SHORT_LIVED

Create file as temporary and if possible do not flush to disk. The pmode argument is required when _O_CREAT is specified.

_O_CREAT | _O_TEMPORARY

Create file as temporary; file is deleted when last file handle is closed. The pmode argument is required when _O_CREAT is specified.

_O_CREAT | _O_EXCL

Returns error value if file specified by filename exists. Applies only when used with _O_CREAT.

_O_NOINHERIT

Prevents creation of a shared file handle.

_O_RANDOM

Specifies primarily random access from disk.

_O_RDONLY

Opens file for reading only; cannot be specified with _O_RDWR or _O_WRONLY.

_O_RDWR

Opens file for both reading and writing; cannot be specified with _O_RDONLY or _O_WRONLY.

_O_SEQUENTIAL

Specifies primarily sequential access from disk

_O_TEXT

Opens file in text (translated) mode. (For more information, see Text and Binary Mode File I/O and fopen.)

_O_TRUNC

Opens file and truncates it to zero length; the file must have write permission. You cannot specify this flag with _O_RDONLY. _O_TRUNC used with _O_CREAT opens an existing file or creates a new file.

Warning   The _O_TRUNC flag destroys the contents of the specified file.

_O_WRONLY

Opens file for writing only; cannot be specified with _O_RDONLY or _O_RDWR.

To specify the file access mode, you must specify either _O_RDONLY, _O_RDWR, or _O_WRONLY. There is no default value for the access mode.

The argument shflag is a constant expression consisting of one of the following manifest constants, defined in SHARE.H.

_SH_DENYRW

Denies read and write access to file

_SH_DENYWR

Denies write access to file

_SH_DENYRD

Denies read access to file

_SH_DENYNO

Permits read and write access

The pmode argument is required only when you specify _O_CREAT. If the file does not exist, pmode specifies the file’s permission settings, which are set when the new file is closed the first time. Otherwise pmode is ignored. pmode is an integer expression that contains one or both of the manifest constants _S_IWRITE and _S_IREAD, defined in SYS\STAT.H. When both constants are given, they are combined with the bitwise-OR operator. The meaning of pmode is as follows:

_S_IWRITE

Writing permitted

_S_IREAD

Reading permitted

_S_IREAD | _S_IWRITE

Reading and writing permitted

If write permission is not given, the file is read-only. Under Windows NT and Windows 95, all files are readable; it is not possible to give write-only permission. Thus the modes _S_IWRITE and _S_IREAD | _S_IWRITE are equivalent.

_sopen applies the current file-permission mask to pmode before setting the permissions (see _umask).

Example

/* LOCKING.C: This program opens a file with sharing. It locks
 * some bytes before reading them, then unlocks them. Note that the
 * program works correctly only if the file exists.
 */

#include <io.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/locking.h>
#include <share.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>

void main( void )
{
   int  fh, numread;
   char buffer[40];

   /* Quit if can't open file or system doesn't 
    * support sharing. 
    */
   fh = _sopen( "locking.c", _O_RDWR, _SH_DENYNO, 
                 _S_IREAD | _S_IWRITE );
   if( fh == -1 )
      exit( 1 );

   /* Lock some bytes and read them. Then unlock. */
   if( _locking( fh, LK_NBLCK, 30L ) != -1 )
   {
      printf( "No one can change these bytes while I'm reading them\n" );
      numread = _read( fh, buffer, 30 );
      printf( "%d bytes read: %.30s\n", numread, buffer );
      lseek( fh, 0L, SEEK_SET );
     _locking( fh, LK_UNLCK, 30L );
      printf( "Now I'm done. Do what you will with them\n" );
   }
   else
      perror( "Locking failed\n" );

   _close( fh );
}

Output

No one can change these bytes while I'm reading them
30 bytes read: /* LOCKING.C: This program ope
Now I'm done. Do what you will with them

Low-level I/O Routines

See Also   _close, _creat, fopen, _fsopen, _open