The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.
The latest version of this topic can be found at _sopen_s, _wsopen_s.
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, );
The file handle, or -1 in the case of an error.
The kind of operations allowed.
The kind of sharing allowed.
A nonzero return value indicates an error; in that case
errno is set to one of the following values.
The given path is a directory, or the file is read-only, but an open-for-writing operation was attempted.
_O_EXCL flags were specified, but
filename already exists.
pmode argument, 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 is returned.
For more information about these and other return codes, see errno, _doserrno, _sys_errlist, and _sys_nerr.
In the case of an error, -1 is returned through
pfh is a null pointer).
_sopen_s function opens the file specified by
filename and prepares the file for shared reading or writing, as defined by
_wsopen_s is a wide-character version of
filename argument to
_wsopen_s is a wide-character string.
_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, which are defined in <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 a file and opens it for writing. Has no effect if the file specified by
_O_CREAT | _O_SHORT_LIVED
Creates a file as temporary and if possible does not flush to disk.
_O_CREAT | _O_TEMPORARY
Creates a file as temporary; the file is deleted when the last file descriptor is closed.
_O_CREAT | _O_EXCL
Returns an error value if the file specified by
filename exists. Applies only when used with
Prevents creation of a shared file descriptor.
Specifies primarily random access from disk.
Opens a file for reading only. Cannot be specified with
Opens a file for both reading and writing. Cannot be specified with
Specifies primarily sequential access from disk.
Opens a file and truncates it to zero length; the file must have write permission. Cannot be specified with
_O_TRUNC used with
_O_CREAT opens an existing file or creates a file.
_O_TRUNC flag destroys the contents of the specified file.
Opens a file for writing only. Cannot be specified with
Opens a file in Unicode UTF-16 mode.
Opens a file in Unicode UTF-8 mode.
Opens a file in Unicode mode.
To specify the file access mode, you must specify either
_O_WRONLY. There is no default value for the access mode.
When a file is opened in Unicode mode by using
_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.
_sopen_s is called with
_O_WRONLY | _O_APPEND (append mode) and
_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.
shflag is a constant expression that consists of one of the following manifest constants, which are 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.
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_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.
_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_IREAD | _S_IWRITE are equivalent.
_sopen_s applies the current file-permission mask to
pmode before the permissions are set. (See _umask.)
|Routine||Required header||Optional header|
||<io.h>||<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>|
_wsopen_s are Microsoft extensions. For more compatibility information, see Compatibility.
See the example for _locking.