"如何在 PHP 中检查对象是否为空？"

Question

How to find if an object is empty or not in PHP.

$obj = simplexml_load_file($url);

Answer 1

You can cast to an array and then check if it is empty or not

$arr = (array)$obj;
if (!$arr) {
    // do stuff
}

Answer 2

Edit : I didn't realize they wanted to specifically check if a SimpleXMLElement object is empty. I left the old answer below

Updated Answer (SimpleXMLElement) :

For SimpleXMLElement:

If by empty you mean has no properties:

$obj = simplexml_load_file($url);
if ( !$obj->count() )
{
    // no properties
}

OR

$obj = simplexml_load_file($url);
if ( !(array)$obj )
{
    // empty array
}

If SimpleXMLElement is one level deep, and by empty you actually mean that it only has properties PHP considers falsey (or no properties):

$obj = simplexml_load_file($url);
if ( !array_filter((array)$obj) )
{
    // all properties falsey or no properties at all
}

If SimpleXMLElement is more than one level deep, you can start by converting it to a pure array:

$obj = simplexml_load_file($url);
// `json_decode(json_encode($obj), TRUE)` can be slow because
// you're converting to and from a JSON string.
// I don't know another simple way to do a deep conversion from object to array
$array = json_decode(json_encode($obj), TRUE);
if ( !array_filter($array) )
{
    // empty or all properties falsey
}

---

Old Answer (simple object) :

If you want to check if a simple object (type stdClass ) is completely empty (no keys/values), you can do the following:

// $obj is type stdClass and we want to check if it's empty
if ( $obj == new stdClass() )
{
    echo "Object is empty"; // JSON: {}
}
else
{
    echo "Object has properties";
}

Source: http://php.net/manual/en/language.oop5.object-comparison.php

Edit : added example

$one = new stdClass();
$two = (object)array();

var_dump($one == new stdClass()); // TRUE
var_dump($two == new stdClass()); // TRUE
var_dump($one == $two); // TRUE

$two->test = TRUE;
var_dump($two == new stdClass()); // FALSE
var_dump($one == $two); // FALSE

$two->test = FALSE;
var_dump($one == $two); // FALSE

$two->test = NULL;
var_dump($one == $two); // FALSE

$two->test = TRUE;
$one->test = TRUE;
var_dump($one == $two); // TRUE

unset($one->test, $two->test);
var_dump($one == $two); // TRUE

Answer 3

You can cast your object into an array, and test its count like so:

if(count((array)$obj)) {
   // doStuff
}

Answer 4

Imagine if the object is not empty and in a way quite big, why would you waste the resources to cast it to array or serialize it...

This is a very easy solution I use in JavaScript. Unlike the mentioned solution that casts an object to array and check if it is empty, or to encode it into JSON, this simple function is very efficient concerning used resources to perform a simple task.

function emptyObj( $obj ) {
    foreach ( $obj AS $prop ) {
        return FALSE;
    }

    return TRUE;
}

The solution works in a very simple manner: It wont enter a foreach loop at all if the object is empty and it will return true . If it's not empty it will enter the foreach loop and return false right away, not passing through the whole set.

Answer 5

Using empty() won't work as usual when using it on an object, because the __isset() overloading method will be called instead, if declared.

Therefore you can use count() (if the object is Countable ).

Or by using get_object_vars() , eg

get_object_vars($obj) ? TRUE : FALSE;

Answer 6

Another possible solution which doesn't need casting to array :

// test setup
class X { private $p = 1; } // private fields only => empty
$obj = new X;
// $obj->x = 1;


// test wrapped into a function
function object_empty( $obj ){
  foreach( $obj as $x ) return false;
  return true;
}


// inline test
$object_empty = true;
foreach( $obj as $object_empty ){ // value ignored ... 
  $object_empty = false; // ... because we set it false
  break;
}


// test    
var_dump( $object_empty, object_empty( $obj ) );

Answer 7

there's no unique safe way to check if an object is empty

php's count() first casts to array, but casting can produce an empty array, depends by how the object is implemented (extensions' objects are often affected by those issues)

in your case you have to use $obj->count();

http://it.php.net/manual/en/simplexmlelement.count.php

(that is not php's count http://www.php.net/count )

Answer 8

If you cast anything in PHP as a (bool), it will tell you right away if the item is an object, primitive type or null. Use the following code:

$obj = simplexml_load_file($url);

if (!(bool)$obj) {
    print "This variable is null, 0 or empty";
} else {
    print "Variable is an object or a primitive type!";
}

Answer 9

in PHP version 8

consider you want to access a property of an object, but you are not sure that the object itself is null or not and it could cause error. in this case you can use Nullsafe operator that introduced in php 8 as follow:

 $country = $session?->user?->getAddress()?->country;

Answer 10

I was using a json_decode of a string in post request. None of the above worked for me, in the end I used this:

$post_vals = json_decode($_POST['stuff']);

if(json_encode($post_vals->object) != '{}')
{
    // its not empty
}

Answer 11

$array = array_filter($array);
if(!empty($array)) {
    echo "not empty";
}

or

if(count($array) > 0) {
    echo 'Error';
} else {
    echo 'No Error';
}

Answer 12

Simply check if object type is null or not.

if( $obj !== null )
{
     // DO YOUR WORK
}

Answer 13

Based on this answer from kenorb, here's another one-liner for objects with public vars:

if (!empty(get_object_vars($myObj))) { ... }

For objects with private or protected vars, better to cast to an array as others have mentioned.

Answer 14

If an object is "empty" or not is a matter of definition, and because it depends on the nature of the object the class represents, it is for the class to define.

PHP itself regards every instance of a class as not empty.

class Test { }
$t = new Test();
var_dump(empty($t));

// results in bool(false)

There cannot be a generic definition for an "empty" object. You might argue in the above example the result of empty() should be true , because the object does not represent any content. But how is PHP to know? Some objects are never meant to represent content (think factories for instance), others always represent a meaningful value (think new DateTime() ).

In short, you will have to come up with your own criteria for a specific object, and test them accordingly, either from outside the object or from a self-written isEmpty() method in the object.