(PHP 4 >= 4.2.0, PHP 5)

ftokConvert a pathname and a project identifier to a System V IPC key


int ftok ( string $pathname , string $proj )

The function converts the pathname of an existing accessible file and a project identifier into an integer for use with for example shmop_open() and other System V IPC keys.



Path to an accessible file.


Project identifier. This must be a one character string.

Return Values

On success the return value will be the created key value, otherwise -1 is returned.

See Also

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User Contributed Notes 8 notes

abk at avatartechnology dot com
10 years ago
Thanks to  daniele_dll@yahoo.it who got this in turn from linux glibc 2.3.2: http://www.php.net/manual/en/function.shmop-open.php -- I'm putting this here because it might be helpful to others.

function ftok($pathname, $proj_id) {
   $st = @stat($pathname);
   if (!$st) {
       return -1;
   $key = sprintf("%u", (($st['ino'] & 0xffff) | (($st['dev'] & 0xff) << 16) | (($proj_id & 0xff) << 24)));
   return $key;
david dot rech at virusmedia dot de
10 years ago
Missing ftok() on Windows? Here's my little workaround:

if( !function_exists('ftok') )
ftok($filename = "", $proj = "")
        if( empty(
$filename) || !file_exists($filename) )
            return -
$filename = $filename . (string) $proj;
$key = array(); sizeof($key) < strlen($filename); $key[] = ord(substr($filename, sizeof($key), 1)));

NOTE: There *may* be duplicate keys, even if probability is low.

The key's were NOT computed like the original UNIX ftok() because i.e. fileinode() is also missing on windows. Normally ftok() computes a key based on the file inode and the system minor id of the harddrive the file resides.

Behaviour is like PHPs ftok(), -1 is returned if file is missing or $filename is empty, computed int as hex on success.

David Rech
vlatko dot surlan at evorion dot hr
1 year ago
The rather unintuitive usage of ftok with shm related functions like shmop_open and shm_attach could simply be explained as a need to avoid shm key collisions. Using ftok with a file that belongs to your project is likely to generate a unique key. Additionally, using ftok with a file from your project avoids the need to store the key so that other processes can access the segment because ftok will always give you the same key if you pass the same file.
marco at greenlightsolutions dot nl
7 years ago
As ftok uses only the last 16 bits of the inode of the file, you can get collisions on large filesystems. Unfortunately, on large filesystems you can get collisions rather quickly: if you have a collection of 350-400 files, odds are that two of them have inodes with the same last 16 bits. So I've taken to using fileinode instead of ftok with functions like shmop_open.
7 years ago
mbowie at buzmo dot com wrote:
"The result of this is that if you're using "1" as the id on the PHP side, you'll need to use 49 elsewhere."

You can always use chr() as an alternative.
mbowie at buzmo dot com
10 years ago
If you're planning to use ftok() to generate an IPC identifier to share with other applications, note that PHP uses the ASCII value of the proj parameter to generate the key, not the proj (aka id) parameter itself.

The result of this is that if you're using "1" as the id on the PHP side, you'll need to use 49 elsewhere.

This may not be the case under all OS's, but certainly is for FreeBSD which requires the id parameter passed to ftok to be an int.

Also of note, ipcs and ipcrm are extremely useful for debugging SysV queues etc.

kimaz at swecom dot org
10 years ago
You dont have to use ftok() for specifying an System V IPC identifier, though its a good thing to do so.

Passing a regular int to, e.g. msg_get_queue, will have the same effect aslong as you use that value when reading/writing.

I use it for some minor tasks generating small queue's.
andreyKEINSPAM at php dot net
10 years ago
This function is not part neither of ext/sysvsem nor ext/sysvshm but comes with the core functions of PHP (from ext/standard).
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