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_sopen, _wsopen | Microsoft Docs
11/04/2016
cpp-standard-libraries
reference
_sopen
_wsopen
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DLLExport
_wsopen
wsopen
_sopen
_tsopen
C++
sopen function
sharing files
opening files, for sharing
_sopen function
wsopen function
files [C++], opening
files [C++], sharing
_wsopen function
a9d4cccf-06e9-414d-96fa-453fca88cc1f
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cplusplus

_sopen, _wsopen

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

Syntax

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 The kind of operations allowed.

shflag The kind 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.

errno value Condition
EACCES The given path is a directory, or the 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 are available.
ENOENT File or path is 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, which are defined in <fcntl.h>. When two or more constants form the argument oflag, they are combined with the bitwise-OR operator ( | ).

oflag constant Behavior
_O_APPEND Moves the file pointer to the end of the file before every write operation.
_O_BINARY Opens the file in binary (untranslated) mode. (See fopen for a description of binary mode.)
_O_CREAT Creates a file and opens it 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 Creates a file as temporary and if possible does not flush to disk. The pmode argument is required when _O_CREAT is specified.
_O_CREAT | _O_TEMPORARY Creates 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 that caching is optimized for, but not restricted to, random access from disk.
_O_RDONLY Opens a file for reading only. Cannot be specified with _O_RDWR or _O_WRONLY.
_O_RDWR Opens a file for both reading and writing. Cannot be specified with _O_RDONLY or _O_WRONLY.
_O_SEQUENTIAL Specifies that caching is optimized for, but not restricted to, 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. Cannot be specified with _O_RDONLY. _O_TRUNC used with _O_CREAT opens an existing file or creates a 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 Opens a file in Unicode UTF-16 mode.
_O_U8TEXT Opens a file in Unicode UTF-8 mode.
_O_WTEXT Opens a file in Unicode mode.

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.

When a file is opened in Unicode mode by using _O_WTEXT, _O_U8TEXT, or _O_U16TEXT, input functions translate the data that's read from the file into UTF-16 data stored as type wchar_t. Functions that write to a file opened in Unicode mode expect buffers that contain UTF-16 data stored as type wchar_t. If the file is encoded as UTF-8, then UTF-16 data is translated into UTF-8 when it is written, and the file's UTF-8-encoded content is translated into UTF-16 when it is read. An attempt to read or write an odd number of bytes in Unicode mode causes a parameter validation error. To read or write data that's stored in your program as UTF-8, use a text or binary file mode instead of a Unicode mode. You are responsible for any required encoding translation.

If _sopen is called with _O_WRONLY | _O_APPEND (append mode) and _O_WTEXT, _O_U16TEXT, or _O_U8TEXT, it first tries 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 opens the file for writing only and uses the default value for the Unicode mode setting.

The argument shflag is a constant expression consisting of one of the following manifest constants, which are defined in <share.h>.

shflag constant Behavior
_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 _O_CREAT is specified. 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, which are 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.

pmode Meaning
_S_IREAD Only reading permitted.
_S_IWRITE Writing permitted. (In effect, permits reading and writing.)
_S_IREAD | _S_IWRITE Reading and writing permitted.

If write permission is not given, the file is read-only. In the Windows operating system, all files are readable; it is not possible to give write-only permission. Therefore, the modes _S_IWRITE and _S_IREAD | _S_IWRITE are equivalent.

_sopen applies the current file-permission mask to pmode before the permissions are set. (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.

Example

See the example for _locking.

See also

Low-Level I/O
_close
_creat, _wcreat
fopen, _wfopen
_fsopen, _wfsopen
_open, _wopen