(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)

ftokConvertit un chemin et un identifiant de projet en une clé System V IPC


ftok(string $filename, string $project_id): int

Convertit le paramètre filename d'un fichier existant, et de l'identifiant de projet proj, en un entier integer à utiliser avec la fonction shmop_open() et d'autres fonctions System V IPC.

Liste de paramètres


Chemin vers un fichier accessible.


Identifiant du projet. Doit être un seul caractère.

Valeurs de retour

En cas de succès, la valeur retournée sera la valeur de la clé créée, sinon, -1 sera retourné.

Voir aussi

  • shmop_open() - Crée ou ouvre un bloc de mémoire partagée
  • sem_get() - Retourne un identifiant de sémaphore

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User Contributed Notes 6 notes

abk at avatartechnology dot com
19 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;
vlatko dot surlan at evorion dot hr
11 years 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.
david dot rech at virusmedia dot de
19 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
mbowie at buzmo dot com
19 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.

seelts at gmail dot com
9 years ago
abk@avatartechnology.com has copied the code of daniele_dll@yahoo.it
But it is not correct.
The right version is here:
function ftok ($filePath, $projectId) {
$fileStats = stat($filePath);
if (!
$fileStats) {
return -

$fileStats['ino'] & 0xffff) | (($fileStats['dev'] & 0xff) << 16) | ((ord($projectId) & 0xff) << 24)

The difference is that $projectId string should be used as ASCII value via ord() function. Otherwise it will be interpreted as 0.
marco at greenlightsolutions dot nl
17 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.
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