Open a file for shared access
Synopsis:
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <share.h>
int sopen( const char* filename,
int oflag,
int share,
... );
Arguments:
- filename
- The path name of the file that you want to open.
- oflag
- Flags that specify the status and access modes of the file.
This argument is a combination of the following bits (defined in
<fcntl.h>):
- O_RDONLY — permit the file to be only read.
- O_WRONLY — permit the file to be only written.
- O_RDWR — permit the file to be both read and written.
- O_APPEND — cause each record that's written
to be written at the end of the file.
- O_CREAT — create the file if it doesn't exist.
This bit has no effect if the file already exists.
- O_TRUNC — truncate the file to contain no data
if the file exists; this bit has no effect if the file doesn't exist.
- O_EXCL — open the file for exclusive access.
If the file exists and you also specify O_CREAT,
the open fails (that is, use O_EXCL
to ensure that the file doesn't already exist).
- share
- The shared access for the file.
This is a combination of the following bits (defined in <share.h>):
- SH_COMPAT — this flag is ignored in the QNX implementation.
- SH_DENYRW — prevent read or write access to the file.
- SH_DENYWR — prevent write access to the file.
- SH_DENYRD — prevent read access to the file.
- SH_DENYNO — permit both read and write access to the file.
If you set O_CREAT in oflag, you must also
specify the following argument:
- mode_t mode
- An object of type mode_t that specifies the access mode
that you want to use for a newly created file.
For more information, see the entry for
struct stat.
Library:
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
Description:
The sopen() function opens a file at the operating system level for
shared access. The name of the file to be opened is given by
filename.
The file is accessed according to the access mode specified by oflag.
You must specify O_CREAT if the file doesn't exist.
The sharing mode of the file is given by the share
argument. The optional argument is the file permissions to be used when
O_CREAT flag is on in the oflag mode;
you must provide this when the file is to be created.
The sopen() function applies the current file permission mask
to the specified permissions (see
umask()).
Note that:
open( path, oflag, ... );
is the same as:
sopen( path, oflag, SH_DENYNO, ... );
Note:
The
sopen() function ignores advisory locks that you may
have set by calling
fcntl().
Returns:
A descriptor for the file, or -1 if an error occurs while opening the file
(errno is set).
Errors:
- EACCES
- Search permission is denied on a component of the path prefix, or the
file exists and the permissions specified by oflag
are denied, or the file doesn't exist and write permission is denied
for the parent directory of the file to be created.
- EBUSY
- Sharing mode (share) was denied due to a conflicting open.
- EEXIST
- The O_CREAT and O_EXCL flags are set, and the named file exists.
- EISDIR
- The named file is a directory, and the oflag
argument specifies write-only or read/write access.
- ELOOP
- Too many levels of symbolic links or prefixes.
- EMFILE
- All file descriptors available to the process are currently open.
- ENOENT
- Path or file not found.
- ENOSYS
- The sopen() function isn't implemented for the
filesystem specified in path.
Examples:
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <share.h>
int main( void )
{
int filedes;
/* open a file for output */
/* replace existing file if it exists */
filedes = sopen( "file",
O_WRONLY | O_CREAT | O_TRUNC,
SH_DENYWR,
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP );
/* read a file which is assumed to exist */
filedes = sopen( "file", O_RDONLY, SH_DENYWR );
/* append to the end of an existing file */
/* write a new file if file doesn't exist */
filedes = sopen( "file",
O_WRONLY | O_CREAT | O_APPEND,
SH_DENYWR,
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP );
return EXIT_SUCCESS;
}
Classification:
Unix
Safety: |
|
Cancellation point |
Yes |
Interrupt handler |
No |
Signal handler |
No |
Thread |
Yes |