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FTOK(P) FTOK(P)
NAME
ftok - generate an IPC key
SYNOPSIS
#include <sys/ipc.h>
key_t ftok(const char *path, int id);
DESCRIPTION
The ftok() function shall return a key based on path and id that is usable in sub-
sequent calls to msgget(), semget(), and shmget(). The application shall ensure
that the path argument is the pathname of an existing file that the process is able
to stat().
The ftok() function shall return the same key value for all paths that name the
same file, when called with the same id value, and return different key values when
called with different id values or with paths that name different files existing on
the same file system at the same time. It is unspecified whether ftok() shall
return the same key value when called again after the file named by path is removed
and recreated with the same name.
Only the low-order 8-bits of id are significant. The behavior of ftok() is unspeci-
fied if these bits are 0.
RETURN VALUE
Upon successful completion, ftok() shall return a key. Otherwise, ftok() shall
return (key_t)-1 and set errno to indicate the error.
ERRORS
The ftok() function shall fail if:
EACCES Search permission is denied for a component of the path prefix.
ELOOP A loop exists in symbolic links encountered during resolution of the path
argument.
ENAMETOOLONG
The length of the path argument exceeds {PATH_MAX} or a pathname component
is longer than {NAME_MAX}.
ENOENT A component of path does not name an existing file or path is an empty
string.
ENOTDIR
A component of the path prefix is not a directory.
The ftok() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of
the path argument.
ENAMETOOLONG
Pathname resolution of a symbolic link produced an intermediate result whose
length exceeds {PATH_MAX}.
The following sections are informative.
EXAMPLES
Getting an IPC Key
The following example gets a unique key that can be used by the IPC functions
semget(), msgget(), and shmget(). The key returned by ftok() for this example is
based on the ID value S and the pathname /tmp.
#include <sys/ipc.h>
...
key_t key;
char *path = "/tmp";
int id = â€â€™Sâ€â€™;
key = ftok(path, id);
Saving an IPC Key
The following example gets a unique key based on the pathname /tmp and the ID value
a. It also assigns the value of the resulting key to the semkey variable so that it
will be available to a later call to semget(), msgget(), or shmget().
#include <sys/ipc.h>
...
key_t semkey;
if ((semkey = ftok("/tmp", â€â€™aâ€â€™)) == (key_t) -1) {
perror("IPC error: ftok"); exit(1);
}
APPLICATION USAGE
For maximum portability, id should be a single-byte character.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
msgget() , semget() , shmget() , the Base Definitions volume of
IEEE Std 1003.1-2001, <sys/ipc.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C)
2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The
Open Group. In the event of any discrepancy between this version and the original
IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is
the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
POSIX 2003 FTOK(P)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2008-12-02 05:53 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)