What is stdClass in PHP?

stdClass is just a generic 'empty' class that's used when casting other types to objects. Despite what the other two answers say, stdClass is not the base class for objects in PHP. This can be demonstrated fairly easily:

class Foo{}
$foo = new Foo();
echo ($foo instanceof stdClass)?'Y':'N';
// outputs 'N'

I don't believe there's a concept of a base object in PHP

stdClass is PHP's generic empty class, kind of like Object in Java or object in Python (Edit: but not actually used as universal base class; thanks @Ciaran for pointing this out).

It is useful for anonymous objects, dynamic properties, etc.

An easy way to consider the StdClass is as an alternative to associative array. See this example below that shows how json_decode() allows to get an StdClass instance or an associative array. Also but not shown in this example, SoapClient::__soapCall returns an StdClass instance.

<?php
//Example with StdClass
$json = '{ "foo": "bar", "number": 42 }';
$stdInstance = json_decode($json);
echo $stdInstance->foo . PHP_EOL; //"bar"
echo $stdInstance->number . PHP_EOL; //42
//Example with associative array
$array = json_decode($json, true);
echo $array['foo'] . PHP_EOL; //"bar"
echo $array['number'] . PHP_EOL; //42

See Dynamic Properties in PHP and StdClass for more examples.

The reason why we have stdClass is because in PHP there is no way to distinguish a normal array from an associate array (like in Javascript you have {} for object and [] for array to distinguish them).

So this creates a problem for empty objects. Take this for example.

PHP:

$a = [1, 2, 3]; // this is an array
$b = ['one' => 1, 'two' => 2]; // this is an associate array (aka hash)
$c = ['a' => $a, 'b' => $b]; // this is also an associate array (aka hash)

Let's assume you want to JSON encode the variable $c

echo json_encode($c);
// outputs => {'a': [1,2,3], 'b': {one: 1, two: 2}}

Now let's say you deleted all the keys from $b making it empty. Since $b is now empty (you deleted all the keys remember?), it looks like [] which can be either an array or object if you look at it.

So if you do a json_encode again, the output will be different

echo json_encode($c);
// outputs => {'a': [1,2,3], 'b': []}

This is a problem because we know b that was supposed to be an associate array but PHP (or any function like json_encode) doesn't.

So stdClass comes to rescue. Taking the same example again

$a = [1, 2, 3]; // this is an array
$b = (object) ['one' => 1, 'two' => 2]; // this makes it an stdClass
$c = ['a' => $a, 'b' => $b]; // this is also an associate array (aka hash)

So now even if you delete all keys from $b and make it empty, since it is an stdClass it won't matter and when you json_encode it you will get this:

echo json_encode($c);
// outputs => {'a': [1,2,3], 'b': {}}

This is also the reason why json_encode and json_decode by default return stdClass.

 $c = json_decode('{"a": [1,2,3], "b": {}}', true); //true to deocde as array
 // $c is now ['a' => [1,2,3], 'b' => []] in PHP
 // if you json_encode($c) again your data is now corrupted

Its also worth noting that by using Casting you do not actually need to create an object as in the answer given by @Bandula. Instead you can simply cast your array to an object and the stdClass is returned. For example:

$array = array(
    'Property1'=>'hello',
    'Property2'=>'world',
    'Property3'=>'again',
);

$obj = (object) $array;
echo $obj->Property3;

Output: again

stdclass is a way in which the php avoid stopping interpreting the script when there is some data must be put in a class , but unfortunately this class was not defined

Example :

 return $statement->fetchAll(PDO::FETCH_CLASS  , 'Tasks');

Here the data will be put in the predefined 'Tasks' . But, if we did the code as this :

 return $statement->fetchAll(PDO::FETCH_CLASS );

then the php will put the results in stdclass .

simply php says that : look , we have a good KIDS[Objects] Here but without Parents . So , we will send them to a infant child Care Home stdclass :)

stdClass in PHP is classic generic class. It has no built-in properties or methods. Basically, It's used for casting the types, creating objects with dynamic properties, etc. If you have the javascript background, You can determine as

$o = new \stdClass();

is equivalent to

const o = {};

It creates empty object, later populated by the program control flow.