ftok(S-osr5)

ftok -- standard interprocess communication package

Syntax

cc . . . -lc

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

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

Description

All interprocess communication facilities require you to supply a key that the msgget(S-osr5), semget(S-osr5), and shmget(S-osr5) system calls use to obtain interprocess communication identifiers. One suggested method for forming a key is to use the ftok subroutine. 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 standards for forming them. If a standard is not adhered to, unrelated processes may conflict. Therefore, the most significant byte of a key should refer to a project.

ftok returns a key based on path and id that is usable in subsequent msgget, semget, and shmget system calls. path must be the pathname of an existing file that is accessible to the process. id is a character which uniquely identifies a project. ftok returns the same key for linked files when called with the same id and returns different keys when called with the same file name but different ids.

Diagnostics

ftok returns (key_t) -1 if path does not exist or is not accessible to the process.

Warning

If the file whose path is passed to ftok is removed when keys still refer to the file, future calls to ftok with the same path and id return an error. If the same file is recreated, then ftok is likely to return a different key than it did the first time it was called.

Standards conformance