FTOK(3)                    Linux Programmer's Manual                   FTOK(3)

NAME
       ftok  -  convert  a pathname and a project identifier to a System V IPC
       key

SYNOPSIS
       #include <sys/types.h>
       #include <sys/ipc.h>

       key_t ftok(const char *pathname, int proj_id);

DESCRIPTION
       The ftok() function uses the identity of the file named  by  the  given
       pathname  (which  must  refer  to an existing, accessible file) and the
       least significant 8 bits of proj_id (which must be nonzero) to generate
       a  key_t  type  System  V  IPC  key,  suitable  for use with msgget(2),
       semget(2), or shmget(2).

       The resulting value is the same for all pathnames that  name  the  same
       file,  when  the  same  value  of  proj_id is used.  The value returned
       should be different when the (simultaneously  existing)  files  or  the
       project IDs differ.

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

ATTRIBUTES
   Multithreading (see pthreads(7))
       The ftok() function is thread-safe.

CONFORMING TO
       POSIX.1-2001.

NOTES
       On some ancient systems, the prototype was:

              key_t ftok(char *pathname, char proj_id);

       Today,  proj_id  is  an  int,  but still only 8 bits are used.  Typical
       usage has an ASCII character proj_id, that is why the behavior is  said
       to be undefined when proj_id is zero.

       Of  course,  no  guarantee  can  be  given  that the resulting key_t is
       unique.  Typically, a best-effort attempt combines  the  given  proj_id
       byte,  the  lower  16 bits of the inode number, and the lower 8 bits of
       the device number into a 32-bit result.  Collisions may easily  happen,
       for example between files on /dev/hda1 and files on /dev/sda1.

SEE ALSO
       msgget(2), semget(2), shmget(2), stat(2), svipc(7)

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.

GNU                               2014-08-19                           FTOK(3)

Czas wygenerowania: 0.00050 sek.

Created with the man page lookup class by Andrew Collington.
Based on a C man page viewer by Vadim Pavlov
Unicode soft-hyphen fix (as used by RedHat) by Dan Edwards
Some optimisations by Eli Argon
Caching idea and code contribution by James Richardson

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