ftok(3)ftok(3)Nameftok - standard interprocess communication package
Syntax
#include <sys/types.h>
#include <sys/ipc.h>
key_t ftok(path, id)
char ∗path;
char id;
Description
All interprocess communication facilities require the user to supply a
key to be used by the and system calls to obtain interprocess communi‐
cation identifiers. One suggested method for forming a key is to use
the file to key, subroutine described below. Another way to compose
keys is to include the project ID in the most significant byte and to
use the remaining portion as a sequence number. There are many other
ways to form keys, but it is necessary for each system to define stan‐
dards for forming them. If some standard is not adhered to, it will be
possible for unrelated processes to unintentionally interfere with each
other's operation. Therefore, it is strongly suggested that the most
significant byte of a key in some sense refer to a project so that keys
do not conflict across a given system.
The subroutine returns a key based on path and id that is usable in
subsequent and system calls. The path must be the path name of an
existing file that is accessible to the process. The id is a character
which uniquely identifies a project. Note that will return the same
key for linked files when called with the same id and that it will
return different keys when called with the same file name but different
ids.
Return Values
The subroutine returns (key_t) -1 if path does not exist or if it is
not accessible to the process.
Warning
If the file whose path is passed to is removed when keys still refer to
the file, future calls to with the same path and id will return an
error. If the same file is recreated, then is likely to return a dif‐
ferent key than it did the original time it was called.
See Alsointro(2), msgget(2), semget(2), shmget(2)ftok(3)
