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 ( mixed $class , string $property ) : bool

本函数检查给出的 property 是否存在于指定的类中（以及是否能在当前范围内访问）。

Note:

As opposed with isset(), property_exists() returns true even if the property has the value null.

参数

class

字符串形式的类名或要检查的类的一个对象

property

属性的名字

返回值

如果该属性存在则返回 true，如果不存在则返回 false，出错返回 null。

注释

Note:

如果此类不是已知类，使用此函数会使用任何已注册的 autoloader。

Note:

The property_exists() function cannot detect properties that are magically accessible using the __get magic method.

更新日志

版本 说明
5.3.0 This function checks the existence of a property independent of accessibility.

范例

Example #1 A property_exists() example

<?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, as of PHP 5.3.0
var_dump(property_exists('myClass', 'bar'));    //false
var_dump(property_exists('myClass', 'test'));   //true, as of PHP 5.3.0
myClass::test();

?>

参见

User Contributed Notes

rnealxp at yahoo dot com 11-May-2020 06:56
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
?>
@fitorec 14-Jul-2019 02:12
<?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
David Spector 03-Sep-2018 12:37
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.
falundir at gmail dot com 16-Feb-2017 08:42
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
?>
Daniel dot Peder at infoset dot com 23-Nov-2016 09:24
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)

*/
saurabh dot agarwal89 at gmail dot com 27-May-2015 11:17
$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)
g dot gentile at parentesigraffe dot com 05-Mar-2015 09:02
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()
ewisuri [gmail] 15-Feb-2014 04:37
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
Nanhe Kumar 17-Jan-2014 10:39
<?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
?>
Stefan W 03-Sep-2013 01:23
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
?>
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