Submit a Pull Request Report a Bug

property_exists

(PHP 5 >= 5.1.0, PHP 7, PHP 8)

property_exists — 检查对象或类是否具有该属性

说明

property_exists(object|string $object_or_class, string $property): bool

本函数检查给出的 property 是否存在于指定的类中。

注意:
跟 isset() 的区别是即使属性的值为 null，property_exists() 也会返回 true。

参数

object_or_class: 需要检查的类名或者类的对象
property: 属性的名称

返回值

如果属性存在则返回 true，不存在则返回 false。如果发生错误则返回 null。

示例

示例 #1 property_exists() 示例

<?php

class myClass {
    public $mine;
    private $xpto;
    static protected $test;

    static function test() {
        var_dump(property_exists('myClass', 'xpto')); //true
    }
}

var_dump(property_exists('myClass', 'mine'));   //true
var_dump(property_exists(new myClass, 'mine')); //true
var_dump(property_exists('myClass', 'xpto'));   //true
var_dump(property_exists('myClass', 'bar'));    //false
var_dump(property_exists('myClass', 'test'));   //true
myClass::test();

?>

注释

注意:
如果此类不是已知类，使用此函数会使用任何已注册的 autoloader。

注意:
property_exists() 函数不能检查通过 __get 魔术方法访问的属性。

参见

method_exists() - 检查类的方法是否存在

＋add a note

User Contributed Notes 12 notes

down

g dot gentile at parentesigraffe dot com ¶

8 years ago

The function behaves differently depending on whether the property has been present in the class declaration, or has been added dynamically, if the variable has been unset()

<?php

class TestClass {

    public $declared = null;
    
}

$testObject = new TestClass;

var_dump(property_exists("TestClass", "dynamic")); // boolean false, as expected
var_dump(property_exists($testObject, "dynamic")); // boolean false, same as above

$testObject->dynamic = null;
var_dump(property_exists($testObject, "dynamic")); // boolean true

unset($testObject->dynamic);
var_dump(property_exists($testObject, "dynamic")); // boolean false, again.

var_dump(property_exists($testObject, "declared")); // boolean true, as espected

unset($testObject->declared);
var_dump(property_exists($testObject, "declared")); // boolean true, even if has been unset()

down

Stefan W ¶

10 years ago

If you are in a namespaced file, and you want to pass the class name as a string, you will have to include the full namespace for the class name - even from inside the same namespace:

<?
namespace MyNS;

class A {
    public $foo;
}

property_exists("A", "foo");          // false
property_exists("\\MyNS\\A", "foo");  // true
?>

down

Nanhe Kumar ¶

9 years ago

<?php

class Student {

    protected $_name;
    protected $_email;
    

    public function __call($name, $arguments) {
        $action = substr($name, 0, 3);
        switch ($action) {
            case 'get':
                $property = '_' . strtolower(substr($name, 3));
                if(property_exists($this,$property)){
                    return $this->{$property};
                }else{
                    echo "Undefined Property";
                }
                break;
            case 'set':
                $property = '_' . strtolower(substr($name, 3));
                if(property_exists($this,$property)){
                    $this->{$property} = $arguments[0];
                }else{
                    echo "Undefined Property";
                }
                
                break;
            default :
                return FALSE;
        }
    }

}

$s = new Student();
$s->setName('Nanhe Kumar');
$s->setEmail('nanhe.kumar@gmail.com');
echo $s->getName(); //Nanhe Kumar
echo $s->getEmail(); // nanhe.kumar@gmail.com
$s->setAge(10); //Undefined Property
?>

down

ewisuri [gmail] ¶

9 years ago

As of PHP 5.3.0, calling property_exists from a parent class sees private properties in sub-classes.

<?php
class P {
    public function test_prop($prop) { return property_exists($this, $prop); }
}

class Child extends P {
    private $prop1;
}

$child = new Child();
var_dump($child->test_prop('prop1')); //true, as of PHP 5.3.0

down

saurabh dot agarwal89 at gmail dot com ¶

8 years ago

$a = array('a','b'=>'c');
print_r((object) $a);
var_dump( property_exists((object) $a,'0'));
var_dump( property_exists((object) $a,'b'));

OUTPUT:
stdClass Object
(
    [0] => a
    [b] => c
)
bool(false)
bool(true)

down

biziclop ¶

8 days ago

I needed a method for finding out if accessing a property outside a class is possible without errors/warnings, considering that the class might use the magic methods __isset/__get to simulate nonexistent properties.

<?php
// returns true if property is safely accessible publicly by using $obj->$prop
// Tested with PHP 5.1 - 8.2, see https://3v4l.org/QBTd1
function public_property_exists( $obj, $prop ){
  // allow magic $obj->__isset( $prop ) to execute if exists
  if( isset( $obj->$prop ))  return true;
  
  // no public/protected/private property exists with this name
  if( ! property_exists( $obj, $prop ))  return false;

  // the property exists, but is it public?
  $rp = new ReflectionProperty( $obj, $prop );
  return $rp->isPublic();
}

//// Test/demo
class C {
  public    $public    = "I’m public!";
  protected $protected = "I’m public!";
  private   $private   = "I’m public!";
  function __isset( $k ){
    return substr( $k, 0, 5 ) === 'magic';
  }
  function __get( $k ){
    if( $k === 'magic_isset_but_null')  return null;
    return "I’m {$k}!";
  }
}

$o = new C();
foreach( array(
  'public', 'protected', 'private',
  'magic', 'magic_isset_but_null',
  'missing'
) as $prop ){
  if( public_property_exists( $o, $prop ))
        echo "\$o->{$prop} is a public property, its value is: ",
             var_export( $o->$prop, true ), "\n";
  else  echo "\$o->{$prop} is not a public property.\n";
}
/*
$o->public    is a public property, its value is: 'I’m public!'
$o->protected is not a public property.
$o->private   is not a public property.
$o->magic     is a public property, its value is: 'I’m magic!'
$o->magic_isset_but_null is a public property, its value is: NULL
$o->missing   is not a public property.
*/

down

anonymous ¶

18 days ago

Be wary if you're checking for nested properties. This function returns true for null values. If you're not checking for null, you will throw a fatal error if you then try to pass a property that exists, but equals null into the first argument.

down

rnealxp at yahoo dot com ¶

3 years ago

For class constants, use defined() to check for their existence since property_exists() cannot be used.
<?php
class A{
    private static $c = 'C';
    const B = 'B';
}
if(property_exists('A','c')===true){
    echo 'y';
}else{
    echo 'n';
} //output: y
if(property_exists('A','B')===true){
    echo 'y';
}else{
    echo 'n';
} //output: n
if(defined('A::B')===true){
    echo 'y';
}else{
    echo 'n';
} //output: y
?>

down

@fitorec ¶

4 years ago

<?php

abstract class P {
  private $priv;
  static protected $static_prop;
  static function exists($prop = 'priv') {
      var_dump(property_exists(new static, $prop)); //true
  }
}

class S extends P {
  static protected $new_prop;
}
S::exists('new_prop');       // True
S::exists('static_prop');    // True
S::exists('priv');           // True

down

-1

falundir at gmail dot com ¶

6 years ago

If you want to test if declared *public* property was unset, you can use the following code:

<?php
class A {
    public $declared;
}

$a = new A();
$is_defined = array_key_exists('declared', (array)$a); //=>true

unset($a->declared);
$is_defined = array_key_exists('declared', (array)$a); //=>false
?>

down

-3

Daniel dot Peder at infoset dot com ¶

6 years ago

declared properties cannot be unset
any set property does exist, even being set to null, regardless how it was set

<?php

class demo_property_exists {

    public $my_public;
    protected $my_protected;
    private $my_private;

    function __construct() {
        $this->dumper('before-constructed');
        $this->my_constructed_int = 123;
        $this->my_constructed_null = null;
        $this->dumper('after-constructed');
    }

    public function dumper($name) {
        printf("\n[%s] dump:\n", $name);

        foreach ($this->my_checklist() as $prop) {
            printf("[%s]:\t", $prop);
            var_dump(property_exists($this, $prop));
        }
    }

    public function unset_all() {
        foreach ($this->my_checklist() as $prop) {
            unset($this->$prop);
        }
    }

    private function my_checklist() {
        return array('my_public', 'my_protected', 'my_private', 'my_constructed_int', 'my_constructed_null', 'my_assigned_int', 'my_assigned_null',);
    }

}

$object = new demo_property_exists();
$object->dumper('before-assigned');
$object->my_assigned_int = 456;
$object->my_assigned_null = null;
$object->dumper('after-assigned');
$object->unset_all();
$object->dumper('after-unset');

/*
results:

[before-constructed] dump:
[my_public]:    bool(true)
[my_protected]: bool(true)
[my_private]:   bool(true)
[my_constructed_int]:   bool(false)
[my_constructed_null]:  bool(false)
[my_assigned_int]:      bool(false)
[my_assigned_null]:     bool(false)

[after-constructed] dump:
[my_public]:    bool(true)
[my_protected]: bool(true)
[my_private]:   bool(true)
[my_constructed_int]:   bool(true)
[my_constructed_null]:  bool(true)
[my_assigned_int]:      bool(false)
[my_assigned_null]:     bool(false)

[before-assigned] dump:
[my_public]:    bool(true)
[my_protected]: bool(true)
[my_private]:   bool(true)
[my_constructed_int]:   bool(true)
[my_constructed_null]:  bool(true)
[my_assigned_int]:      bool(false)
[my_assigned_null]:     bool(false)

[after-assigned] dump:
[my_public]:    bool(true)
[my_protected]: bool(true)
[my_private]:   bool(true)
[my_constructed_int]:   bool(true)
[my_constructed_null]:  bool(true)
[my_assigned_int]:      bool(true)
[my_assigned_null]:     bool(true)

[after-unset] dump:
[my_public]:    bool(true)
[my_protected]: bool(true)
[my_private]:   bool(true)
[my_constructed_int]:   bool(false)
[my_constructed_null]:  bool(false)
[my_assigned_int]:      bool(false)
[my_assigned_null]:     bool(false)

*/

down

-12

David Spector ¶

5 years ago

Just to clarify, property_exists only works for static properties. There is no corresponding const_exists function in PHP to do something similar for const names.

＋add a note