trusty (3) ftok.3posix.gz

NAME

       ftok - generate an IPC key

SYNOPSIS

       #include <sys/ipc.h>

       key_t ftok(const char *path, int id);

DESCRIPTION

       The  ftok()  function  shall  return  a  key  based  on path and id that is usable in subsequent calls to
       msgget(), semget(), and shmget(). The application shall ensure that the path argument is the pathname  of
       an existing file that the process is able to stat().

       The  ftok()  function  shall return the same key value for all paths that name the same file, when called
       with the same id value, and return different key values when called with  different  id  values  or  with
       paths  that  name  different  files  existing on the same file system at the same time. It is unspecified
       whether ftok() shall return the same key value when called again after the file named by path is  removed
       and recreated with the same name.

       Only  the low-order 8-bits of id are significant. The behavior of ftok() is unspecified if these bits are
       0.

RETURN VALUE

       Upon successful completion, ftok() shall return a key. Otherwise, ftok() shall return (key_t)-1  and  set
       errno to indicate the error.

ERRORS

       The ftok() function shall fail if:

       EACCES Search permission is denied for a component of the path prefix.

       ELOOP  A loop exists in symbolic links encountered during resolution of the path argument.

       ENAMETOOLONG
              The  length  of  the  path  argument  exceeds  {PATH_MAX}  or  a pathname component is longer than
              {NAME_MAX}.

       ENOENT A component of path does not name an existing file or path is an empty string.

       ENOTDIR
              A component of the path prefix is not a directory.

       The ftok() function may fail if:

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

       ENAMETOOLONG
              Pathname resolution of a symbolic link  produced  an  intermediate  result  whose  length  exceeds
              {PATH_MAX}.

       The following sections are informative.

EXAMPLES

   Getting an IPC Key
       The  following  example  gets  a unique key that can be used by the IPC functions semget(), msgget(), and
       shmget(). The key returned by ftok() for this example is based on the ID value S and the pathname /tmp.

              #include <sys/ipc.h>
              ...
              key_t key;
              char *path = "/tmp";
              int id = 'S';

              key = ftok(path, id);

   Saving an IPC Key
       The following example gets a unique key based on the pathname /tmp and the ID value a.  It  also  assigns
       the  value  of  the  resulting key to the semkey variable so that it will be available to a later call to
       semget(), msgget(), or shmget().

              #include <sys/ipc.h>
              ...
              key_t semkey;

              if ((semkey = ftok("/tmp", 'a')) == (key_t) -1) {
                  perror("IPC error: ftok"); exit(1);
              }

APPLICATION USAGE

       For maximum portability, id should be a single-byte character.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       msgget() , semget() , shmget() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/ipc.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .