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_sopen_s, _wsopen_s

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Opens a file for sharing. These versions of _sopen and _wsopen have security enhancements, as described in Security features in the CRT.

Syntax

errno_t _sopen_s(
   int* pfh,
   const char *filename,
   int oflag,
   int shflag,
   int pmode
);
errno_t _wsopen_s(
   int* pfh,
   const wchar_t *filename,
   int oflag,
   int shflag,
   int pmode,
);

Parameters

pfh
The file handle, or -1 if there's an error.

filename
File name.

oflag
The kind of operations allowed.

shflag
The kind of sharing allowed.

pmode
Permission setting.

Return value

A nonzero return value indicates an error; in that case errno is set 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, shflag, or pmode argument, or pfh or filename was a null pointer.
EMFILE No more file descriptors available.
ENOENT File or path not found.

If an invalid argument is passed to the function, the invalid parameter handler is invoked, as described in Parameter validation. If execution is allowed to continue, errno is set to EINVAL, and EINVAL is returned.

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

If there's an error, -1 is returned through pfh (unless pfh is a null pointer).

Remarks

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

By default, this function's global state is scoped to the application. To change it, see Global state in the CRT.

Generic-text routine mappings

Tchar.h routine _UNICODE and _MBCS not defined _MBCS defined _UNICODE defined
_tsopen_s _sopen_s _sopen_s _wsopen_s

The integer expression oflag is formed by combining one or more manifest constants, which are defined in <fcntl.h>. When two or more constants form the argument oflag, they're 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 doesn't 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. To preserve legacy behavior for app-compatibility, other processes aren't prevented from deleting this file.
_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. Can't be specified with _O_RDWR or _O_WRONLY.
_O_RDWR Opens a file for both reading and writing. Can't 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 ANSI 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. Can't 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. Can't 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's 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's written. The file's UTF-8-encoded content is translated into UTF-16 when it's 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're responsible for any required encoding translation.

If _sopen_s 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 that consists 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 always required, unlike in _sopen. When you specify _O_CREAT, if the file doesn't 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're 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 isn't given, the file is read-only. In the Windows operating system, all files are readable; it isn't possible to give write-only permission. Therefore, the modes _S_IWRITE and _S_IREAD | _S_IWRITE are equivalent.

_sopen_s applies the current file-permission mask to pmode before the permissions are set. (See _umask.)

Requirements

Function Required header Optional header
_sopen_s <io.h> <fcntl.h>, <sys\types.h>, <sys\stat.h>, <share.h>
_wsopen_s <io.h> or <wchar.h> <fcntl.h>, <sys/types.h>, <sys/stat.h>, <share.h>

_sopen_s and _wsopen_s are Microsoft extensions. 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