ftok(3) - c7

1FTOK(3)                    Linux Programmer's Manual                   FTOK(3)
2
3
4

NAME

6       ftok  -  convert  a pathname and a project identifier to a System V IPC
7       key
8

SYNOPSIS

10       #include <sys/types.h>
11       #include <sys/ipc.h>
12
13       key_t ftok(const char *pathname, int proj_id);
14

DESCRIPTION

16       The ftok() function uses the identity of the file named  by  the  given
17       pathname  (which  must  refer  to an existing, accessible file) and the
18       least significant 8 bits of proj_id (which must be nonzero) to generate
19       a  key_t  type  System  V  IPC  key,  suitable  for use with msgget(2),
20       semget(2), or shmget(2).
21
22       The resulting value is the same for all pathnames that  name  the  same
23       file,  when  the  same  value  of  proj_id is used.  The value returned
24       should be different when the (simultaneously  existing)  files  or  the
25       project IDs differ.
26

RETURN VALUE

28       On  success,  the  generated key_t value is returned.  On failure -1 is
29       returned, with errno indicating the error as  for  the  stat(2)  system
30       call.
31

CONFORMING TO

33       POSIX.1-2001.
34

NOTES

36       Under libc4 and libc5 (and under SunOS 4.x) the prototype was:
37
38              key_t ftok(char *pathname, char proj_id);
39
40       Today proj_id is an int, but still only 8 bits are used.  Typical usage
41       has an ASCII character proj_id, that is why the behavior is said to  be
42       undefined when proj_id is zero.
43
44       Of course no guarantee can be given that the resulting key_t is unique.
45       Typically, a best effort attempt combines the given proj_id  byte,  the
46       lower  16  bits of the inode number, and the lower 8 bits of the device
47       number into a 32-bit result.  Collisions may easily happen, for example
48       between files on /dev/hda1 and files on /dev/sda1.
49

COLOPHON

54       This  page  is  part of release 3.53 of the Linux man-pages project.  A
55       description of the project, and information about reporting  bugs,  can
56       be found at http://www.kernel.org/doc/man-pages/.
57
58
59
60GNU                               2001-11-28                           FTOK(3)