spl_object_hash

(PHP 5 >= 5.2.0, PHP 7, PHP 8)

spl_object_hash — 返回指定对象的 hash id

说明

spl_object_hash(object $object): string

本函数为对象返回唯一标识符。只要对象没有销毁，这个 id 可用作保存对象的散列键，或者用于标识对象。一旦对象销毁，它的散列值可能会被其它对象重用。此行为类似为 spl_object_id()。

参数

object: 任何对象。

返回值

字符串，对于当前存在的每个对象都是唯一的，且对同一个对象始终相同。

示例

示例 #1 A spl_object_hash() 示例

<?php
$id = spl_object_hash($object);
$storage[$id] = $object;
?>

注释

注意:
当对象销毁后，它的散列值可能会被其它对象重用。

注意:
对象散列应该使用 === 和 !== 标识符比较，因为返回的散列可能是数字字符串。例如：0000000000000e600000000000000000。

参见

spl_object_id() - Return the integer object handle for given object

改进此页面

了解如何改进此页面 • 提交拉取请求 • 报告一个错误

＋添加备注

用户贡献的备注 11 notes

down

107

planetbeing ¶

17 years ago

Note that the contents (properties) of the object are NOT hashed by the function, merely its internal handle and handler table pointer. This is sufficient to guarantee that any two objects simultaneously co-residing in memory will have different hashes. Uniqueness is not guaranteed between objects that did not reside in memory simultaneously, for example:

var_dump(spl_object_hash(new stdClass()), spl_object_hash(new stdClass()));

Running this alone will usually generate the same hashes, since PHP reuses the internal handle for the first stdClass after it has been dereferenced and destroyed when it creates the second stdClass.

down

mjs at beebo dot org ¶

11 years ago

Note that given two different objects spl_object_hash() can return values that look very similar, and in fact both the most significant *and* least significant digits are likely to be identical!  e.g. "000000003cc56d770000000007fa48c5" and "000000003cc56d0d0000000007fa48c5".

Therefore (especially if using this function for debugging), you may wish to pass the hash into a cryptographic hash function like md5() to get to facilitate visual comparisons, and make it more likely that the first few or last few digits are unique.

md5("000000003cc56d770000000007fa48c5") -> "619a799747d348fa1caf181a72b65d9f"

md5("000000003cc56d0d0000000007fa48c5") -> "ae964bc912281e7804fe5a88b4546cb2"

down

A simple developer ¶

1 year ago

Attention when comparing object hashes in PHP >= 8.1

In PHP 8.1 (I think) the output of spl_object_hash() changed (see pull request https://github.com/php/php-src/pull/7010).
This lead to a strange misbehaviour of our application, as we stored object hashes in an array to check, if we processed object already. A simple in_array() check returned true, even though the current object hash was NOT actually in array.

Actual problem: New hashes are much more simple and can be something like "0000000000000e600000000000000000" or "0000000000000e490000000000000000", which PHP will interpret as numeric (exponent).
in_array() will compare non type-safe by default and will interpret named hashes as "0".

down

aa dot vasilenko at gmail dot com ¶

6 years ago

Please note that since PHP 7.2 there's new function available spl_object_id() which returns int instead of string. It's (supposed to be) more performant. Due to lack of documentation I recommend you reading the PR https://github.com/php/php-src/pull/2611

down

DimeCadmium ¶

6 years ago

For those who believe this function is misnamed, I would like to direct you to https://en.wikipedia.org/wiki/Hash_function . Also, for those who think it's misnamed and supply a comparison to Python, I would like to direct you to https://docs.python.org/2/library/functions.html#hash which does the same thing as this function. (From Python's data-model docs: "User-defined classes have __cmp__() and __hash__() methods by default; ... x.__hash__() returns a result derived from id(x)." - id(x) returns the memory address of the object.)

The cryptographic hash functions you are familiar with, like MD5 or SHA1, are named hash functions because they have a similar design goal: low chance of collisions.

down

Hayleu Watson ¶

7 years ago

The "hash" mentioned in the name of this function refers to the storage structure known as a "hash table", not to any sort of "message digest". The string returned by this function is little more than the object's address in the (hash) table PHP maintains of all existing objects.

down

Numety ¶

10 months ago

As others have noted, this function now returns the ID, padded with zeroes.
It does not produce a cryptographic hash (which is not what the name hints at, either), nor does it hide it which order the objects were created.

If you wish to give your objects unique identifiers while hiding in which order they were created, you can achieve this by hashing their ID together with other predictable values:

<?php

function objectHash(object $object): string
{
    return hash('sha512', $object::class . spl_object_id($object));
}

?>

Here's an example usage:

<?php

class Person
{
    function __construct(public string $name) {}
}

$anna = new Person('Anna');
$bob = new Person('Bob');

var_export(objectHash($anna));   // '077d33c1 etc.
echo "\n";
var_export(objectHash($bob));    // 'ea3c1319 etc.

?>

Feel free to choose another hash, or hash other values along with their ID, for it to better suit your environment.

down

Hayley Watson ¶

1 year ago

This function is slightly older than spl_object_id. Its output is more complex but doesn't actually provide any more information than the newer function. It used to be a lot more complex (without being any more informative) but now it's merely the object's ID number written in hex with a lot of padding to maintain the old format. spl_object_id just gives the ID number as a plain integer.

You're probably better off using spl_object_id, and thinking about migrating if you're already using spl_object_hash; there is a chance this function will be deprecated and subsequently removed in the future.

down

-1

jasonlester at nope dot com ¶

10 months ago

obj->handle is an unsigned long that starts a 0 and is incremented by 1 every time an object is created, it is not a true pointer such as if created by mallaoc() or similar.

/* {{{ Returns the integer object handle for the given object */
PHP_FUNCTION(spl_object_id)
{
    zend_object *obj;

    ZEND_PARSE_PARAMETERS_START(1, 1)
        Z_PARAM_OBJ(obj)
    ZEND_PARSE_PARAMETERS_END();

    RETURN_LONG((zend_long)obj->handle);
}
/* }}} */

PHPAPI zend_string *php_spl_object_hash(zend_object *obj) /* {{{*/
{
    return strpprintf(32, "%016zx0000000000000000", (intptr_t)obj->handle);
}
/* }}} */

down

-2

Hayley Watson ¶

7 years ago

The "hash" mentioned in this function is used in the sense of the storage structure known as a "hash table", not in the sense of "message digest".

down

-5

Ulrich Eckhardt ¶

7 years ago

Calling this a hash is very misleading:

1. This function gives an object identifier (ID), which uniquely identifies the object for its whole lifetime. This is similar to the address of an object in C or the id() function in Python. I'm sure other languages have similar constructs.
2. This is not a hash and has nothing to do with it. A hash takes data and algorithmically reduces that data to some kind of scalar value. The only guarantee is that two equal inputs provide the same output, but not that two different inputs provide different outputs (hint: hash collisions). spl_object_hash() guarantees different outputs for non-identical objects though.
3. As someone mentioned already, this does not look at the content of the object. If you consider the difference between equality and identity, it only allows determining identity. If you serialize and unserialize an object, it will not be identical to its former self, but it will be equal, just to give an example. If you want a key to use in a response cache, using this function on the request is not only useless, because equal requests have different IDs, but possibly even harmful, because when a request object is garbage collected, its ID can be reused.