PHP 7.0.6 Released

    serialize

    (PHP 4, PHP 5, PHP 7)

    serialize — Generates a storable representation of a value

    Description

    string serialize ( mixed $value )

    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().

    Parameters

    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 serializing 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.

    Note:

    Object's private members have the class name prepended to the member name; protected members have a '*' prepended to the member name. These prepended values have null bytes on either side.

    Return Values

    Returns a string containing a byte-stream representation of value that can be stored anywhere.

    Note that this is a binary string which may include null bytes, and needs to be stored and handled as such. For example, serialize() output should generally be stored in a BLOB field in a database, rather than a CHAR or TEXT field.

    Examples

    Example #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.. */
            }
    }
    ?>

    Notes

    Note:

    Note that many built-in PHP objects cannot be serialized. However, those with this ability either implement the Serializable interface or the magic __sleep() and __wakeup() methods. If an internal class does not fulfill any of those requirements, it cannot reliably be serialized.

    There are some historical exceptions to the above rule, where some internal objects could be serialized without implementing the interface or exposing the methods. Notably, the ArrayObject prior to PHP 5.2.0.

    Warning

    When serialize() serializes objects, the leading backslash is not included in the class name of namespaced classes for maximum compatibility.

    See Also

    User Contributed Notes

    egingell at sisna dot com
    9 years ago
    <?
    /*
    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.
    */
    ?>
    Anonymous
    4 years ago
    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.
    nh at ngin dot de
    3 years ago
    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).
    frost at easycast dot ru
    2 years ago
    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'
    ?>
    Nanhe Kumar
    2 years ago
    Note : You cannot save the state of a static variable by serializing.
    <?php
    /*
    * student.class.php
    */
    class Student {

        public     $name;
        private     $roll;
        protected     $age;
        static     $class;

        public function     __construct() {
                $this->name = "Nanhe Kumar";
                $this->roll = 1;
                $this->age = 16;
                Student::$class = "10+2";
        }

    }
    ?>
    <?php
    /**
    * serialize.php
    */
    include_once("student.class.php");

    //Serialize
    $so = new Student();
    $serialized = serialize($so);
    file_put_contents("test.txt", $serialized);
    echo     $serialized; //O:7:"Student":3:{s:4:"name";s:11:"Nanhe Kumar";s:13:"Studentroll";i:1;s:6:"*age";i:16;}
    ?>
    <?php
    /**
    * unserialize.php
    */
    include_once("student.class.php");
    $content = file_get_contents("test.txt");
    $unserialized = unserialize($content);
    print_r($unserialized);//Student Object ( [name] => Nanhe Kumar [roll:Student:private] => 1 [age:protected] => 16 )
    ?>
    MC_Gurk at gmx dot net
    10 years ago
    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.
    Andrew B
    3 years ago
    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>";
    ?>
    wiart at yahoo dot com
    11 years ago
    Warning: on 64 bits machines,  if you use a long string only composed of numbers as a key in an array and serialize/unserialize it, you can run into problems:

    an example code:
    $arr["20041001103319"] = 'test';
    var_dump( $arr);
    $arr_in_str = serialize($arr);
    print "Now result is: $arr_in_str<BR />";
    $final_arr = unserialize($arr_in_str);
    print "The final unserialized array:<BR />";
    var_dump($final_arr);

    The result:
    array(1) { [20041001103319]=>  string(4) "test" }
    Now result is: a:1:{i:20041001103319;s:4:"test";}
    The final unserialized array:
    array(1) { [683700183]=> string(4) "test" }

    As you can see, the original array :
    $arr["20041001103319"] = "test"

    after serialize/unserialize is:
    $arr[683700183] = "test"

    As you can see,  the key has changed ...

    Apparently a problem of implicit casting + integer overflow (I posted a PHP bug report: http://bugs.php.net/bug.php?id=31117)

    I tested with the latest 4.3.10 compiled on my laptop (32 bits, Mandrake 9.1) --> no such problem. But compiled on AMD 64 bits (Red Hat Taroon), the problem is present.

    Hope this will help some of you to not loose almost a whole day of debugging ;-)
    barbuj at NOSPAM dot yahoo dot com
    8 years ago
    In my specific situation, I wanted to be able to pass some data from page to page, but without relying on a session variable. The answer I came up with was to serialize() the object in question, pass it on to the next page as a hidden form field, then unserialize() it. When ALL class variables are public, this worked fine. However, if there was at least one private/protected variable, the code no longer worked as expected ("Fatal error: Call to a member function display() on a non-object in page2.php on line 4")

    As others have already mentioned, private/protected class variables will not behave nicely (private variables are prefixed by class_name + &#65533;, while protected variables are only prefixed by &#65533; - when looking at the page source using Firefox). Internet Explorer does NOT display the extra character between the class name and variable name, but the code still doesn't work as one would expect.

    Suppose you have a simple class:

    testclass.php
    =============
    <?php
    class TestClass {
      var     $i = 1;

      function     display() {
        echo     "i=" . $this->i;
      }
    ?>

    page1.php
    =========
    <?php
          require_once 'testclass.php';
          $tc = new TestClass;
          $tc->display();
    ?>
    <form method = "post" action = "page2.php">
    <input type = "hidden" name = "str" value = "<?php echo htmlspecialchars( serialize( $tc ) ); ?>">
    <input type = "submit">
    </form>

    page2.php
    =========
    <?php
          require_once 'testclass.php';
          $tc = unserialize( stripslashes( htmlspecialchars_decode( $_POST["str"] ) ) );
          $tc->display();
    ?>

    The fix, suggested by evulish on #php/irc.dal.net, is to replace htmlspecialchars()/htmlspecialchars_decode() by base64_encode()/base64_decode. The code becomes:

    page1.php
    =========
    <input type = "hidden" name = "str" value = "<?php echo base64_encode( serialize( $tc ) ); ?>">

    page2.php
    =========
    <?php
      $tc     = unserialize( base64_decode( $_POST["str"] ) );
    ?>

    Hope this will help someone...
    MiChAeLoKGB
    11 months ago
    I did some testing to see the speed differences between serialize and json_encode, and my results with 250 iterations are:

    PHP serialized in 0.0651714730263 seconds average
    JSON encoded in 0.0254955434799 seconds average
    json_encode() was roughly 155.62% faster than serialize()
    Test took 27.2039430141 seconds with 300 iretations.

    PHP serialized in 0.0564563179016 seconds average
    JSON encoded in 0.0249140485128 seconds average
    json_encode() was roughly 126.60% faster than serialize()
    Test took 24.4148340225 seconds with 300 iretations.

    From all my tests it looks like json_encode is on average about 120% faster (sometimes it gets to about 85% and sometimes to 150%).

    Here is the PHP code you can run on your server to try it out:

    <?php

    // fillArray function myde by Peter Bailey
    function fillArray($depth, $max){
        static     $seed;
        if (    is_null($seed)){
                $seed = array('a', 2, 'c', 4, 'e', 6, 'g', 8, 'i', 10);
        }
        if (    $depth < $max){
                $node = array();
            foreach (    $seed as $key){
                    $node[$key] = fillArray( $depth + 1, $max );
            }
            return     $node;
        }
        return     'empty';
    }

    function     testSpeed($testArray, $iterations = 100){

            $json_time = array();
            $serialize_time = array();
            $test_start = microtime(true);

        for (    $x = 1; $x <= $iterations; $x++){
                $start = microtime(true);
                json_encode($testArray);
                $json_time[] = microtime(true) - $start;

                $start = microtime(true);
                serialize($testArray);
                $serialize_time[] = microtime(true) - $start;
        }

            $test_lenght = microtime(true) - $test_start;
            $json_average = array_sum($json_time) / count($json_time);
            $serialize_average = array_sum($serialize_time) / count($serialize_time);

            $result = "PHP serialized in ".$serialize_average." seconds average<br>";
            $result .= "JSON encoded in ".$json_average." seconds average<br>";

        if (    $json_average < $serialize_average){
                $result .= "json_encode() was roughly ".number_format( ($serialize_average / $json_average - 1 ) * 100, 2 )."% faster than serialize()<br>";
        } else if (     $serializeTime < $jsonTime ){
                $result .= "serialize() was roughly ".number_format( ($json_average / $serialize_average - 1 ) * 100, 2 )."% faster than json_encode()<br>";
        } else {
                $result .= "No way!<br>";
        }

            $result .= "Test took ".$test_lenght." seconds with ".$iterations." iterations.";

        return     $result;

    }

    // Change the number of iterations (250) to lower if you exceed your maximum execution time
    echo testSpeed(fillArray(0, 5), 250);

    ?>
    pli9 at itsa dot ucsf dot edu
    13 years ago
    I have also written some code for importing serialized PHP data into PERL and then writing it back into PHP.  I think the similar library posted above is actually more robust for a few select cases, but mine is more compact and a little easier to follow.  I'd really like comments if anyone finds this useful or has improvements.  Please credit me if you use my code.

    http://www.hcs.harvard.edu/~pli/code/serialPHP.pm
    hfuecks at phppatterns dot com
    12 years ago
    Regarding serializing PHP data types to Javascript, following Ivans note below, theres an example at http://www.tekool.net/php/js_serializer/.

    The basic serialization looks good although, in its current form, it works on the basis of generating Javascript source which a browser executes as a page loads. Using Javascripts eval() the same can be done with strings containing Javascript if youre working with something like XMLHTTPRequest
    Ates Goral
    9 years ago
    Corrections/clarifications to  "Anatomy of a serialize()'ed value":

    All strings appear inside quotes. This applies to string values, object class names and array key names. For example:

    s:3:"foo"
    O:7:"MyClass":1:{...
    a:2:{s:3:"bar";i:42;...

    Object property names and values are delimited by semi-colons, not colons. For example:

    O:7:"MyClass":2:{s:3:"foo";i:10;s:3:"bar";i:20}

    Double/float values are represented as:

    d:0.23241446
    allan666 at gmail.com
    3 years ago
    Oddly, if you serialize a class that was previously unserialized, the class of the variable changes to string... Example:

    $R = unserialize($serialized_object);
    $R->method(); // this is ok
    $str = serialize($R);
    echo(get_class($R));

    this will output "string"!!!!! whereas if the first line was

    $R = new my_class();

    it would output "my_class"!

    I don't know if that is a bug, but the manual is not clear about that! (somehow $R in serialize($R) is being passed by reference, since it changes class).
    pgl at yoyo dot org
    5 years ago
    Another suggestion for coping with binary data in serialize()d variables is just to base64_encode() those fields before serializing. It will increase the size of the variable, but not by too much.
    paul at moveNOtoSPAMiceland DOT com
    11 years ago
    I was trying to submit a serialized array through a hidden form field using POST and was having a lot of trouble with the quotes. I couldn't figure out a way to escape the quotes in the string so that they'd show up right inside the form, so only the characters up to the first set of quotes were being sent.

    My solution was to base64_encode() the string, put that in the hidden form field, and send that through the POST method. Then I decoded it (using base64_decode()) on the other end. This seemed to solve the problem.
    stephen dot adamson at smius dot com
    10 years ago
    If you are serializing an object to store it in the database, using __sleep() can save you some space. The following code will not store empty (null) variables in the serialized string. For my purposes this saved a lot of space, since some of the member variables would not be given values.

    function __sleep()
    {
        $allVars = get_object_vars($this);
        $toReturn = array();
        foreach(array_keys($allVars) as $name)
        {
            if (isset($this->$name))
            {
                $toReturn[] = $name;
            }
        }
        return $toReturn;
    }
    Alexander Podgorny
    10 years ago
    Here is an example of a base class to implement object persistence using serialize and unserialize:

    <?php
    class Persistent
    {
        var     $filename;
           
            /**********************/
            function Persistent($filename)
        {
                $this->filename = $filename;
            if(!    file_exists($this->filename)) $this->save();
        }
            /**********************/
            function save()
        {
            if(    $f = @fopen($this->filename,"w"))
            {
                if(@    fwrite($f,serialize(get_object_vars($this))))
                {
                    @    fclose($f);
                }
                else die(    "Could not write to file ".$this->filename." at Persistant::save");
            }
            else die(    "Could not open file ".$this->filename." for writing, at Persistant::save");
           
        }
            /**********************/
            function open()
        {
                $vars = unserialize(file_get_contents($this->filename));
            foreach(    $vars as $key=>$val)
            {           
                eval(    "$"."this->$key = $"."vars['"."$key'];");
            }
        }
            /**********************/
    }

    ?>

    When an object is extended from this one it can be easily saved and re-opened using it's own methods as follows:

    <?

    class foo extends Persistent
    {
       var $counter;
       function inc()
       {
           $this->counter++;
       }
    }

    $fooObj = new $foo;
    $foo->open();
    print $foo->counter; // displays incrementing integer as page reloads
    $foo->inc();
    $foo->save();

    ?>
    Anonymous
    1 year ago
    For everyone facing the conversion nightmare another Anonymous described here in an older comment (and he took the words out of my mouth), this T-SQL script might be of great help: https://github.com/mjohnsonperl/tsqlphpunserialize/tree/master.

    Please do not follow the path of evil by dumping serialized data into relational databases.
    travis at travishegner dot com
    6 years ago
    If serializing objects to be stored into a postgresql database, the 'null byte' injected for private and protected members throws a wrench into the system. Even pg_escape_bytea() on the value, and storing the value as a binary type fails under certain circumstances.

    For a dirty work around:
    <?php

    $serialized_object     = serialize($my_object);
    $safe_object = str_replace("\0", "~~NULL_BYTE~~", $serialized_object);

    ?>

    this allows you to store the object in a readable text format as well. When reading the data back:

    <?php

    $serialized_object     = str_replace("~~NULL_BYTE~~", "\0", $safe_object);
    $my_object = unserialize($serialized_object);

    ?>

    The only gotcha's with this method is if your object member names or values may somehow contain the odd "~~NULL_BYTE~~" string. If that is the case, then str_replace() to a string that you are guaranteed not to have any where else in the string that serialize() returns.
    Also remember to define the class before calling unserialize().

    If you are storing session data into a postgresql database, then this workaround is an absolute must, because the $data passed to the session's write function is already serialized.

    Thanks,
    Travis Hegner
    Anonymous
    6 years ago
    you should really use mysql_real_escape_string() for escaping (serialized) strings that got thrown into a query (visit php.net/mysql_real_escape_string for further information)
    Jeex
    8 years ago
    It may be worth noting that, depending on the size of the object you are serializing, the serialize function can take up a lot of memory.

    If your script isn't working as expected, your serialize call may have pushed the memory usage over the limit set by memory_limit in php.ini.

    More info on memory limits here: http://www.php.net/manual/en/ini.core.php
    tuxedobob
    1 year ago
    When using serialize() to convert, say, an array to a string to pass via HTML forms, you will likely run into issues with quoting. This is because serialize() puts values in double quotes. The simplest solution is to quote your HTML form value with single quotes rather than double quotes. (This *is* allowed, according to W3C specs.)

    So, instead of:

    <?php
    $arr     = serialize($some_array);
    ?>
    <input type="hidden" name="array" value="$arr" />

    you would want to use:

    <?php
    $arr     = serialize($some_array);
    ?>
    <input type="hidden" name="array" value='$arr' />
    donotmail at me dot com
    6 years ago
    NOTE: php's serialize does not properly serialize arrays with which a slice of the array is a reference to the array itself, observe:

    <?php
    $a     = array();
    $a[0] = "blah";
    $a[1] =& $a;

    $a[1][0] = "pleh"; // $a[0] === "pleh"

    $b = unserialize(serialize($a));

    // $b[0] == "pleh", $b[1][0] == "pleh"

    $b[1][0] = "blah";
    ?>

    now $b[1][0] == "blah", but $b[0] == "pleh"
    after serializing and unserializing, slice 1 is no longer a reference to the array itself... I have found no way around this problem... even manually modifying the serialized string from
    'a:2:{i:0;s:4:"pleh";i:1;a:2:{i:0;s:4:"pleh";i:1;R:3;}}'
    to
    'a:2:{i:0;s:4:"pleh";i:1;R:1;}'

    to force the second slice to be a reference to the first element of the serialization (the array itself), it seemed to work at first glance, but then unreferences it when you alter it again, observe:

    <?php
        $testser     = 'a:2:{i:0;s:4:"pleh";i:1;R:1;}';

            $tmp = unserialize($testser);

            print_r($tmp);

        print     "\n-----------------------\n";

            $tmp[1][0] = "blah";

            print_r($tmp);

    ?>

    outputs:
    Array
    (
        [0] => pleh
        [1] => Array
    *RECURSION*
    )

    -----------------------
    Array
    (
        [0] => pleh
        [1] => Array
            (
                [0] => blah
                [1] => Array
                    (
                        [0] => pleh
                        [1] => Array
    *RECURSION*
                    )

            )

    )
    MarkRoedel at letu dot edu
    16 years ago
    A call to serialize() appears to mess with the array's internal pointer.  If you're going to be walking through your array after serializing it, you'll want to make a call to reset() first.
    friday13 at ig dot com dot br
    8 years ago
    I have problem to use serialize function with hidden form field and the resolution was use htmlentities.

    Ex.:

    <?

    $lista = array( 'pera', 'maça', 'laranja' );

    print "< input type='hidden' name='teste' value='htmlentities( serialize( $lista ) )'" >";

    ?>
    Alessandro Segala
    6 years ago
    I needed to serialize an array to store it inside a database.
    I was looking for a fast, simple way to do serialization, and I came out with 2 options: serialize() or json_encode().

    I ran some benchmarks to see which is the faster, and, surprisingly, I found that serialize() is always between 46% and 96% SLOWER than json_encode().
    So, if you don't need to serialize objects and have the json extension available, consider using it instead of serialize().
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