ftok(3) Library Functions Manual ftok(3)
Name
ftok - 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 commu-
nication identifiers. One suggested method for forming a key is to use the file to key, subroutine described below. Another way to com-
pose 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 standards 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 dif-
ferent 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 different key than it did the original time it was called.
See Also
intro(2), msgget(2), semget(2), shmget(2)
ftok(3)
