NAME
ftok() — create interprocess communication identifier
SYNOPSIS
#include <sys/ipc.h>
key_t ftok(const char *path, int id);
DESCRIPTION
All interprocess communication facilities
require the user to supply a key to be used by the
msgget(),
semget(),
and
shmget()
system calls to obtain interprocess communication identifiers (see
msgget(2),
semget(2),
and
shmget(2)).
ftok()
returns a key based on
path
and
id
that is usable in subsequent
msgget(),
semget(),
and
shmget()
system calls.
The parameters for the
ftok()
function are as follows:
- path
must be the path name of an existing file that is accessible to the process.
- id
is a character that uniquely identifies a project. This means that only the
low order 8-bits of id are significant. Note that
ftok()
returns the same key for linked files
when called with the same
id
and that it returns different keys when
called with the same file name but different
ids.
RETURN VALUE
ftok()
returns
(key_t)-1
if
path
does not exist or if it is not accessible to the process.
EXAMPLES
The following call to
ftok()
returns a key associated with the file
myfile
and id
A:
key_t mykey;
mykey = ftok ("myfile", 'A');
WARNINGS
If the file whose
path
is passed to
ftok()
is removed when keys still refer to the file, future calls to
ftok()
with the same
path
and
id
will return an error.
If the same file is recreated,
ftok()
is likely to return a different key
than it did the original time it was called.
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