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_sopen_s, _wsopen_s

Opens a file for sharing. These are versions of _sopen and _wsopen with security enhancements as described in Security Features in the CRT.

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,

[out] pfh

The file handle, or -1 in the case of an error.

[in] filename

File name.

[in] oflag

Type of operations allowed.

[in] shflag

Type of sharing allowed.

[in] pmode

Permission setting.

A nonzero return value indicates an error, in which case errno is set to one of the following values.


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


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


Invalid oflag, shflag, orpmode argument, or pfh or filename was a null pointer.


No more file descriptors available.


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 _doserrno, errno, _sys_errlist, and _sys_nerr.

In the case of an error, -1 will be returned through pfh (unless pfh is a null pointer).

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.

Generic-Text Routine Mappings

Tchar.h routine

_UNICODE and _MBCS not defined

_MBCS defined

_UNICODE defined





The integer expression oflag is formed by combining one or more 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 ( | ).


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


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


Creates and opens new file for writing. Has no effect if file specified by filename exists.


Create a file as temporary and if possible do not flush to disk.


Create a file as temporary; the file is deleted when the last file descriptor is closed.


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


Prevents creation of a shared file descriptor.


Specifies primarily random access from disk.


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


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


Specifies primarily sequential access from disk.


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


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.


The _O_TRUNC flag destroys the contents of the specified file.


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


Open the file in Unicode UTF-16 mode.


Open the file in Unicode UTF-8 mode.


Open the 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.

If _sopen_s 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.


Denies read and write access to a file.


Denies write access to a file.


Denies read access to a file.


Permits read and write access.

The pmode argument is always required, unlike in _sopen. 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.


Writing permitted.


Reading permitted.


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


Required header

Optional header



<fcntl.h>, <sys/types.h>, <sys/stat.h>, <share.h>


<io.h> or <wchar.h>

<fcntl.h>, <sys/types.h>, <sys/stat.h>, <share.h>

For more compatibility information, see Compatibility in the Introduction.

See the example for _locking.