Manual Pages for UNIX Operating System command usage for man ftok

Standard C Library Functions                             ftok(3C)



NAME
     ftok - generate an IPC key

SYNOPSIS
     #include 

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


DESCRIPTION
     The ftok() function returns a key based on path and id  that
     is  usable  in  subsequent calls to msgget(2), semget(2) and
     shmget(2). The path argument must  be  the  pathname  of  an
     existing file that the process is able to stat(2).


     The ftok() function will return the same key value  for  all
     paths  that name the same file, when called with the same id
     value, and will return different key values when called with
     different id values.


     If the file named by path is removed while still referred to
     by a key, a call to ftok() with the same path and id returns
     an error. If the same file is  recreated,  then  a  call  to
     ftok()  with the same path and id is likely to return a dif-
     ferent key.


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

RETURN VALUES
     Upon successful completion, ftok() returns  a  key.   Other-
     wise,  ftok()  returns  (key_t)-1 and sets errno to indicate
     the error.

ERRORS
     The ftok() function will fail if:

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


     ELOOP           Too many symbolic links were encountered  in
                     resolving path.


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




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Standard C Library Functions                             ftok(3C)



     ENOENT          A component of path does not name an  exist-
                     ing file or path is an empty string.


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



     The ftok() function may fail if:

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


USAGE
     For maximum portability, id should be a single-byte  charac-
     ter.


     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 unintention-
     ally interfere with each other's operation. It is still pos-
     sible  to interfere intentionally. 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.

NOTES
     Since the ftok() function returns a value based  on  the  id
     given  and  the file serial number of the file named by path
     in a type that is no longer large enough to  hold  all  file
     serial  numbers, it may return the same key for paths naming
     different files on large filesystems.

ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:












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Standard C Library Functions                             ftok(3C)



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


SEE ALSO
     msgget(2),  semget(2),  shmget(2),  stat(2),  attributes(5),
     standards(5)









































SunOS 5.11          Last change: 24 Jul 2002                    3