Get Instance ID of an Object in PHP

Have a look at spl_object_hash(). Usage example:

$id = spl_object_hash($object);

Note that you'll need PHP 5 >= 5.2.0 for that to work.

spl_object_hash() could help you out here. It

returns a unique identifier for the object

which is always the same for a given instance.

EDIT after OP comment:

You could implement such a behavior using a static class property, e.g:

class MyClass 
{
    private static $_initialized = false;

    public function __construct()
    {
        if (!self::$_initialized) {
            self::$_initialized = true;
            // your run-only-once code 
        }
    }
}

But actually this has nothing to with your original question.

Alix, your solution in the question was exactly what I needed, but actually breaks when there's an object in an object, returns the last # in the var_dump. I fixed this, made the regex faster, and put it in a nice little function.

/**
 * Get global object ID
 * From: http://stackoverflow.com/questions/2872366/get-instance-id-of-an-object-in-php
 * By: Alix Axel, non-greedy fix by Nate Ferrero
 */
function get_object_id(&$obj) {
    if(!is_object($obj))
        return false;
    ob_start();
    var_dump($obj);// object(foo)#INSTANCE_ID (0) { }
    preg_match('~^.+?#(\d+)~s', ob_get_clean(), $oid);
    return $oid[1]; 
}

Well, yes, with an extension.

Note that the handles used for objects that were, in the meantime, destroyed, can be reused.

Build with phpize && ./configure && make && make install

testext.h

#ifndef PHP_EXTTEST_H
# define PHP_EXTTEST_H
# ifdef HAVE_CONFIG_H
#  include<config.h>
# endif
# include <php.h>
extern zend_module_entry testext_module_entry;
#define phpext_testext_ptr &testext_module_entry
#endif

testext.c

#include "testext.h"

PHP_FUNCTION(get_object_id)
{
    zval *obj;
    if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "o", &obj)
            == FAILURE) {
        return;
    }

    RETURN_LONG(Z_OBJ_HANDLE_P(obj));
}

static zend_function_entry ext_functions[] = {
    PHP_FE(get_object_id, NULL)
    {NULL, NULL, NULL, 0, 0}
};

zend_module_entry testext_module_entry = {
    STANDARD_MODULE_HEADER,
    "testext",
    ext_functions, /* Functions */
    NULL, /* MINIT */
    NULL, /* MSHUTDOWN */
    NULL, /* RINIT */
    NULL, /* RSHUTDOWN */
    NULL, /* MINFO */
    NO_VERSION_YET,
    STANDARD_MODULE_PROPERTIES
};

ZEND_GET_MODULE(testext)

config.m4

PHP_ARG_ENABLE(testext,
  [Whether to enable the "testext" extension],
  [  enable-testext         Enable "testext" extension support])

if test $PHP_EXTTEST != "no"; then
  PHP_SUBST(EXTTEST_SHARED_LIBADD)
  PHP_NEW_EXTENSION(testext, testext.c, $ext_shared)
fi

Test script

<?php
$a = new stdclass();
$b = new stdclass();
var_dump(get_object_id($a));
var_dump(get_object_id($b));

Output

int(1)
int(2)