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HP-UX 11i Version 3: February 2007

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ftok() — create interprocess communication identifier


#include <sys/ipc.h>

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


All interprocess communication facilities require the user to supply a key to be used by the msgget(), semget(), and shmget() system calls to obtain interprocess communication identifiers (see msgget(2), semget(2), and shmget(2)).

ftok() returns a key based on path and id that is usable in subsequent msgget(), semget(), and shmget() system calls.

The parameters for the ftok() function are as follows:


must be the path name of an existing file that is accessible to the process.


is a character that uniquely identifies a project. This means that only the low order 8-bits of id are significant. Note that ftok() returns the same key for linked files when called with the same id and that it returns different keys when called with the same file name but different ids.


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


The following call to ftok() returns a key associated with the file myfile and id A:

key_t mykey; mykey = ftok ("myfile", 'A');


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 will return an error. If the same file is recreated, ftok() is likely to return a different key than it did the original time it was called.

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