_sopen, _wsopen

Article
11/16/2012

Opens a file for sharing. More secure versions of these functions are available; see _sopen_s, _wsopen_s.

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

Parameters

filename
File name.
oflag
Type of operations allowed.
shflag
Type of sharing allowed.
pmode
Permission setting.

Return Value

Each of these functions returns a file descriptor for the opened file.

If filename or oflag is a NULL pointer, or if oflag or shflag is not within a valid range of values, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, these functions return -1 and set errno 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 descriptors available.
ENOENT
File or path not found.

For more information about these and other return codes, see _doserrno, errno, _sys_errlist, and _sys_nerr.

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

Tchar.h routine	_UNICODE and _MBCS not defined	_MBCS defined	_UNICODE defined
_tsopen	_sopen	_sopen	_wsopen

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 a file pointer to the end of the file before every write operation.
_O_BINARY
Opens a 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 the file specified by filename exists. The pmode argument is required when _O_CREAT is specified.
_O_CREAT| _O_SHORT_LIVED
Create a 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 a file as temporary; the file is deleted when the last file descriptor is closed. The pmode argument is required when _O_CREAT is specified.
_O_CREAT| _O_EXCL
Returns an error value if a file specified by filename exists. Applies only when used with _O_CREAT.
_O_NOINHERIT
Prevents creation of a shared file descriptor.
_O_RANDOM
Specifies primarily random access from disk.
_O_RDONLY
Opens a 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 a file in text (translated) mode. (For more information, see Text and Binary Mode File I/O and fopen.)
_O_TRUNC
Opens a 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.

Note

The _O_TRUNC flag destroys the contents of the specified file.
_O_WRONLY
Opens a file for writing only; cannot be specified with _O_RDONLY or _O_RDWR.
_O_U16TEXT
Open the file in Unicode UTF-16 mode. This option is available in Visual C++ 2005.
_O_U8TEXT
Open the file in Unicode UTF-8 mode. This option is available in Visual C++ 2005.
_O_WTEXT
Open the file in Unicode mode. This option is available in Visual C++ 2005.

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.

If _sopen is called with _O_WRONLY|_O_APPEND (append mode) and _O_WTEXT, _O_U16TEXT, or _O_U8TEXT, it will first try to open the file for reading and writing, read the BOM, then reopen it for writing only. If opening the file for reading and writing fails, it will open the file for writing only and use the default value for the Unicode mode setting.

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 a file.
_SH_DENYWR
Denies write access to a file.
_SH_DENYRD
Denies read access to a file.
_SH_DENYNO
Permits read and write access.

The pmode argument is required only when one specifies _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 the Windows operating system, 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).

Requirements

Routine	Required header	Optional header
_sopen	<io.h>	<fcntl.h>, <sys/types.h>, <sys/stat.h>, <share.h>
_wsopen	<io.h> or <wchar.h>	<fcntl.h>, <sys/types.h>, <sys/stat.h>, <share.h>

For more compatibility information, see Compatibility in the Introduction.

Example

See the example for _locking.

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.

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