ftok.3c (2010 09)

ftok(3C) ftok(3C)

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 id s.

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

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.