FTOK(3) Linux Programmer's Manual FTOK(3)NAME
ftok - convert a pathname and a project identifier to a System V IPC key
SYNOPSIS
# include <sys/types.h>
# include <sys/ipc.h>
key_t ftok(const char *pathname, int proj_id);
DESCRIPTION
The ftok function uses the identity of the file named by the given pathname (which must refer to an existing, accessible file) and the
least significant 8 bits of proj_id (which must be nonzero) to generate a key_t type System V IPC key, suitable for use with msgget(2),
semget(2), or shmget(2).
The resulting value is the same for all pathnames that name the same file, when the same value of proj_id is used. The value returned
should be different when the (simultaneously existing) files or the project IDs differ.
RETURN VALUE
On success the generated key_t value is returned. On failure -1 is returned, with errno indicating the error as for the stat(2) system
call.
CONFORMING TO
XPG4
NOTES
Under libc4 and libc5 (and under SunOS 4.x) the prototype was
key_t ftok(char *pathname, char proj_id);
Today proj_id is an int, but still only 8 bits are used. Typical usage has an ASCII character proj_id, that is why the behaviour is said to
be undefined when proj_id is zero.
Of course no guarantee can be given that the resulting key_t is unique. Typically, a best effort attempt combines the given proj_id byte,
the lower 16 bits of the i-node number, and the lower 8 bits of the device number into a 32-bit result. Collisions may easily happen, for
example between files on /dev/hda1 and files on /dev/sda1.
SEE ALSO ipc(5), msgget(2), semget(2), shmget(2), stat(2)Linux 2.4 2001-11-28 FTOK(3)
Check Out this Related Man Page
FTOK(3) Linux Programmer's Manual FTOK(3)NAME
ftok - convert a pathname and a project identifier to a System V IPC key
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
key_t ftok(const char *pathname, int proj_id);
DESCRIPTION
The ftok() function uses the identity of the file named by the given pathname (which must refer to an existing, accessible file) and the
least significant 8 bits of proj_id (which must be nonzero) to generate a key_t type System V IPC key, suitable for use with msgget(2),
semget(2), or shmget(2).
The resulting value is the same for all pathnames that name the same file, when the same value of proj_id is used. The value returned
should be different when the (simultaneously existing) files or the project IDs differ.
RETURN VALUE
On success, the generated key_t value is returned. On failure -1 is returned, with errno indicating the error as for the stat(2) system
call.
CONFORMING TO
POSIX.1-2001.
NOTES
Under libc4 and libc5 (and under SunOS 4.x) the prototype was:
key_t ftok(char *pathname, char proj_id);
Today proj_id is an int, but still only 8 bits are used. Typical usage has an ASCII character proj_id, that is why the behavior is said to
be undefined when proj_id is zero.
Of course no guarantee can be given that the resulting key_t is unique. Typically, a best effort attempt combines the given proj_id byte,
the lower 16 bits of the inode number, and the lower 8 bits of the device number into a 32-bit result. Collisions may easily happen, for
example between files on /dev/hda1 and files on /dev/sda1.
SEE ALSO msgget(2), semget(2), shmget(2), stat(2), svipc(7)COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
GNU 2001-11-28 FTOK(3)
In the system call msgget(key,mode) for the argument key i want to use ftok call . I am really confused with the argument pathname in ftok call. I want to know the pathname of which file I want to specify over there. I am just a beginer to advanced unix plz help me out. (1 Reply)
Hello,
In shared memory, when using shmget function, first parameter is ket_t key.
I know it is an integer type, but length of it is system dependent. That means may not be have integer's ranges.
What is range of key_t in Linux? Is it different in distros, for example in ubuntu & fedora? (2 Replies)
I would like to print value of key generate like this....
key_t k = ftok(".",'c');
printf("key is %d \n" , k);
Is there other way to print this type. I dont think I am getting right output which is
key is 1662074913 (shouldn't it be 6362074913) since 'c' is 63 in hex (ascii table).... (2 Replies)
Greetings:
I am posting this because my searches for this problem only came up with two posts and no helpful suggestions. I have a "solution" (read work-around hack) and have not tried yet to find a root cause, and may never because I am busy doing other things (read working to pay the bills).
... (10 Replies)