OPEN(S) XENIX System V OPEN(S)
Name
open - Opens file for reading or writing.
Syntax
#include <fcntl.h>
int open (path, oflag[, mode])
char *path;
int oflag, mode;
Description
path points to a pathname naming a file. open opens a file
descriptor for the named file and sets the file status flags
according to the value of oflag. oflag values are
constructed by using flags from the following list (only one
of the first three flags below may be used):
O_RDONLY Open for reading only.
O_WRONLY Open for writing only.
O_RDWR Open for reading and writing.
O_NDELAY This flag may affect subsequent reads and writes.
See read(S) and write(S).
When opening a FIFO with O_RDONLY or O_WRONLY set:
If O_NDELAY is set:
An open for reading-only will return without
delay. An open for writing-only will return
an error if no process currently has the file
open for reading.
If O_NDELAY is clear:
An open for reading-only will block until a
process opens the file for writing. An open
for writing-only will block until a process
opens the file for reading.
When opening a file associated with a communication
line:
If O_NDELAY is set:
The open will return without waiting for
carrier.
If O_NDELAY is clear:
The open will block until carrier is present.
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OPEN(S) XENIX System V OPEN(S)
O_APPEND If set, the file pointer will be set to the end of
the file prior to each write.
O_CREAT If the file exists, this flag has no effect.
Otherwise, the file's owner ID is set to the
process' effective user ID, the file's group ID is
set to the process' effective group ID, and the
low-order 12 bits of the file mode are set to the
value of mode modified as follows (see creat(S)):
All bits set in the process' file mode
creation mask are cleared. See umask(S).
The ``save text image after execution bit'' of
the mode is cleared. See chmod(S).
O_TRUNC If the file exists, its length is truncated to 0
and the mode and owner are unchanged.
O_EXCL If O_EXCL and O_CREAT are set, open will fail if
the file exists.
O_SYNCW Every write to this file descriptor will be
synchronous, that is, when the write system call
completes, data is guaranteed to have been written
to disk.
Upon successful completion, a nonnegative integer, the file
descriptor, is returned.
The file pointer used to mark the current position within
the file is set to the beginning of the file.
The new file descriptor is set to remain open across exec
system calls. See fcntl(S).
No process may have more than 60 file descriptors open
simultaneously.
The named file is opened unless one or more of the following
are true:
A component of the path prefix is not a directory.
[ENOTDIR]
O_CREAT is not set and the named file does not exist.
[ENOENT]
A component of the path prefix denies search
permission. [EACCES]
oflag permission is denied for the named file.
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OPEN(S) XENIX System V OPEN(S)
[EACCES]
The named file is a directory and oflag is write or
read/write. [EISDIR]
The named file resides on a read-only file system and
oflag is write or read/write. [EROFS]
Sixty file descriptors are currently open. [EMFILE]
The named file is a character special or block special
file, and the device associated with this special file
does not exist. [ENXIO]
The file is a pure procedure (shared text) file that is
being executed and oflag is write or read/write.
[ETXTBSY]
path points outside the process' allocated address
space. [EFAULT]
O_CREAT and O_EXCL are set, and the named file exists.
[EEXIST]
O_NDELAY is set, the named file is a FIFO, O_WRONLY is
set, and no process has the file open for reading.
[ENXIO]
A signal was caught during the open system call.
[EINTR]
The system file table is full. [ENFILE]
The directory to contain the file cannot be extended,
the file does not exist, and O_CREAT is specified.
[ENOSPC]
Return Value
Upon successful completion, a nonnegative integer, namely a
file descriptor, is returned. Otherwise, a value of -1 is
returned and errno is set to indicate the error.
See Also
chmod(S), close(S), creat(S), dup(S), fcntl(S), lseek(S),
read(S), umask(S), write(S)
Notes
The O_SYNCHW flag is a XENIX specific enhancement which may
not be present in all UNIX implementations.
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