serialize
(PHP 4, PHP 5, PECL axis2:0.1.0-0.1.1)
serialize — Generates a storable representation of a value
Описание
Generates a storable representation of a value
This is useful for storing or passing PHP values around without losing their type and structure.
To make the serialized string into a PHP value again, use unserialize().
Список параметров
- value
-
The value to be serialized. serialize() handles all types, except the resource-type. You can even serialize() arrays that contain references to itself. Circular references inside the array/object you are serialize()ing will also be stored. Any other reference will be lost.
When serializing objects, PHP will attempt to call the member function __sleep prior to serialization. This is to allow the object to do any last minute clean-up, etc. prior to being serialized. Likewise, when the object is restored using unserialize() the __wakeup member function is called.
Возвращаемые значения
Returns a string containing a byte-stream representation of value that can be stored anywhere.
Примеры
Пример #1 serialize() example
<?php
// $session_data contains a multi-dimensional array with session
// information for the current user. We use serialize() to store
// it in a database at the end of the request.
$conn = odbc_connect("webdb", "php", "chicken");
$stmt = odbc_prepare($conn,
"UPDATE sessions SET data = ? WHERE id = ?");
$sqldata = array (serialize($session_data), $_SERVER['PHP_AUTH_USER']);
if (!odbc_execute($stmt, &$sqldata)) {
$stmt = odbc_prepare($conn,
"INSERT INTO sessions (id, data) VALUES(?, ?)");
if (!odbc_execute($stmt, &$sqldata)) {
/* Something went wrong.. */
}
}
?>
Список изменений
| Версия | Описание |
|---|---|
| 4.0.7 | The object serialization process was fixed. |
| 4.0.0 | When serializing an object, methods are not lost anymore. Please see the Serializing Objects for more information. |
Примечания
Замечание: It is not possible to serialize PHP built-in objects.
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- serialize
- settype
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- unserialize
- unset
- var_dump
- var_export
Коментарии
If you are going to serialie an object which contains references to other objects you want to serialize some time later, these references will be lost when the object is unserialized.
The references can only be kept if all of your objects are serialized at once.
That means:
$a = new ClassA();
$b = new ClassB($a); //$b containes a reference to $a;
$s1=serialize($a);
$s2=serialize($b);
$a=unserialize($s1);
$b=unserialize($s2);
now b references to an object of ClassA which is not $a. $a is another object of Class A.
use this:
$buf[0]=$a;
$buf[1]=$b;
$s=serialize($buf);
$buf=unserialize($s);
$a=$buf[0];
$b=$buf[1];
all references are intact.
<?
/*
Anatomy of a serialize()'ed value:
String
s:size:value;
Integer
i:value;
Boolean
b:value; (does not store "true" or "false", does store '1' or '0')
Null
N;
Array
a:size:{key definition;value definition;(repeated per element)}
Object
O:strlen(object name):object name:object size:{s:strlen(property name):property name:property definition;(repeated per property)}
String values are always in double quotes
Array keys are always integers or strings
"null => 'value'" equates to 's:0:"";s:5:"value";',
"true => 'value'" equates to 'i:1;s:5:"value";',
"false => 'value'" equates to 'i:0;s:5:"value";',
"array(whatever the contents) => 'value'" equates to an "illegal offset type" warning because you can't use an
array as a key; however, if you use a variable containing an array as a key, it will equate to 's:5:"Array";s:5:"value";',
and
attempting to use an object as a key will result in the same behavior as using an array will.
*/
?>
Please! please! please! DO NOT serialize data and place it into your database. Serialize can be used that way, but that's missing the point of a relational database and the datatypes inherent in your database engine. Doing this makes data in your database non-portable, difficult to read, and can complicate queries. If you want your application to be portable to other languages, like let's say you find that you want to use Java for some portion of your app that it makes sense to use Java in, serialization will become a pain in the buttocks. You should always be able to query and modify data in the database without using a third party intermediary tool to manipulate data to be inserted.
I've encountered this too many times in my career, it makes for difficult to maintain code, code with portability issues, and data that is it more difficult to migrate to other RDMS systems, new schema, etc. It also has the added disadvantage of making it messy to search your database based on one of the fields that you've serialized.
That's not to say serialize() is useless. It's not... A good place to use it may be a cache file that contains the result of a data intensive operation, for instance. There are tons of others... Just don't abuse serialize because the next guy who comes along will have a maintenance or migration nightmare.
When you serialize an array the internal pointer will not be preserved. Apparently this is the expected behavior but was a bit of a gotcha moment for me. Copy and paste example below.
<?php
//Internal Pointer will be 2 once variables have been assigned.
$array = array();
$array[] = 1;
$array[] = 2;
$array[] = 3;
//Unset variables. Internal pointer will still be at 2.
unset($array[0]);
unset($array[1]);
unset($array[2]);
//Serialize
$serializeArray = serialize($array);
//Unserialize
$array = unserialize($serializeArray);
//Add a new element to the array
//If the internal pointer was preserved, the new array key should be 3.
//Instead the internal pointer has been reset, and the new array key is 0.
$array[] = 4;
//Expected Key - 3
//Actual Key - 0
echo "<pre>" , print_r($array, 1) , "</pre>";
?>
Serializing floating point numbers leads to weird precision offset errors:
<?php
echo round(96.670000000000002, 2);
// 96.67
echo serialize(round(96.670000000000002, 2));
// d:96.670000000000002;
echo serialize(96.67);
// d:96.670000000000002;
?>
Not only is this wrong, but it adds a lot of unnecessary bulk to serialized data. Probably better to use json_encode() instead (which apparently is faster than serialize(), anyway).
Closures cannot be serialized:
<?php
$func = function () {echo 'hello!';};
$func(); // prints "hello!"
$result = serialize($func); // Fatal error: Uncaught exception 'Exception' with message 'Serialization of 'Closure' is not allowed'
?>
There is a type not mentioned in the user notes so far, 'E'. This is the newer Enum class that can be utilised:
login_security|E:25:"Permission:manageClient"