Classes/Object 函数
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property_exists

(PHP 5 >= 5.1.0)

property_exists — 检查对象或类是否具有该属性

说明

bool property_exists ( mixed $class , string $property )

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

Classes/Object 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 检查对象或类是否具有该属性

用户评论:

foddex at foddex dot net (22-Dec-2010 09:56)

Note that before PHP 5.3.3, this function fails for private properties in base classes (which is fixed in 5.3.3)

<?php
class Base {
        private $var = 1;

        public function test() {
                var_dump( property_exists( $this, 'var' ) );
        }
}

class Derived extends Base {
}

$b = new Base();
$b->test();
$d = new Derived();
$d->test();
?>

Executing this code with PHP 5.0 <= x < 5.3 this script echoes (incorrect result):
bool(true)
bool(false)

Executing this code with PHP 5.3 this script echoes (correct result):
bool(true)
bool(true)

webmaster at thedigitalorchard dot ca (25-Apr-2010 05:56)

According to my tests, isset() is 4 times faster than property_exists(), so use a combination of these functions in your programming for best performance.

For example:

<?php

$fld = 'somevar';

if (isset($this->$fld) || property_exists($this, $fld)) {

}

?>

If your programming routinely checks a larger number of property names that are expected to exist, whereas a smaller number may not, then using isset(), as above, will result in faster execution of the programming.

peter at nonumber dot nl (27-Aug-2008 10:48)

The above PHP4 function did not work for me. This does:

<?php
if ( !function_exists( 'property_exists' ) ) {
    function property_exists( $class, $property ) {
        if ( is_object( $class ) ) {
            $vars = get_object_vars( $class );
        } else {
            $vars = get_class_vars( $class );
        }
        return array_key_exists( $property, $vars );
    }
}
?>

rayro at gmx dot de (12-Nov-2007 12:49)

To check the existance of a property from outside the scope (even if it's not accessible) try/consider the following:

<?php
function property_exists_safe($class, $prop)
{
  $r = property_exists($class, $prop);
  if (!$r) {
    $x = new ReflectionClass($class);
    $r = $x->hasProperty($prop);
  }
  return $r;
}

class myClass {
    public $mine;
    private $xpto;

    static function test1() {
        // true, it can be accessed from here
        var_dump(property_exists('myClass', 'xpto'));
    }

    static function test2() {
        // true, it can be accessed from everywhere!
        var_dump(property_exists_safe('myClass', 'xpto'));
    }
}

var_dump(property_exists('myClass', 'mine')); //true
var_dump(property_exists(new myClass, 'mine')); //true
var_dump(property_exists('myClass', 'xpto')); //false, isn't public
myClass::test1();
echo("\n");
var_dump(property_exists_safe('myClass', 'mine')); //true
var_dump(property_exists_safe(new myClass, 'mine')); //true
var_dump(property_exists_safe('myClass', 'xpto')); //true
myClass::test2(); //true
?>

bool(true)
bool(true)
bool(false)
bool(true)

bool(true)
bool(true)
bool(true)
bool(true)

caist at caist dot com (15-Oct-2007 02:19)

A niet way to copy properties from one object to another avoiding stuff like:

$obj2 -> prop1 = $obj1 -> prop1;
$obj2 -> prop2 = $obj1 -> prop2;
$obj2 -> prop3 = $obj1 -> prop3;

...is this loop through all properties:

// copies all property values from obj1 to obj2
foreach ($obj1 as $prop_name => $prop_value)
{
    if (property_exists(get_class($obj2), $prop_name))
                 $obj2 -> {$prop_name} = $prop_value;
}

K (13-Jul-2007 09:11)

to ssettl2 at google's mail >

1) Use self:: in static methods : http://php.net/language.oop5.static

2) Under the description title of this page : "This function checks if the given property exists in the specified class (and if it is ACCESSIBLE FROM THE CURRENT SCOPE)."

This is normal behaviour in PHP5.

Regards

Alan71 (07-Aug-2006 06:57)

This function is case-sensitive, so :

<?php
class Test {
   public $property;
  
   public foo() { echo($property); }
}

property_exists('Test', 'property');   // will return true
property_exists('Test', 'Property');   // will return false
?>

(under PHP5.1.2)

jcaplan at bogus dot amazon dot com (08-Jun-2006 10:35)

The documentation leaves out the important case of new properties you add to objects at run time.  In fact, property_exists will return true if you ask it about such properties.

<?
class Y {}
$y = new Y;

echo isset( $y->prop ) ? "yes\n" : "no\n"; // no;
echo property_exists( 'Y', 'prop' ) ? "yes\n" : "no\n"; // no
echo property_exists( $y, 'prop' ) ? "yes\n" : "no\n"; // no

$y->prop = null;

echo isset( $y->prop ) ? "yes\n" : "no\n"; // no;
echo property_exists( 'Y', 'prop' ) ? "yes\n" : "no\n"; // no
echo property_exists( $y, 'prop' ) ? "yes\n" : "no\n"; // yes
?>

Pete W (01-Jun-2006 07:52)

In a similar vein to the previous note, To check in PHP4 if an object has a property, even if the property is null:

<?php

if(array_key_exists('propertyName',get_object_vars($myObj)))
{
  // ..the property has been defined
} 
?>

timshel (15-Nov-2005 12:20)

I haven't tested this with the exact function semantics of 5.1, but this code should implement this function in php < 5.1:

<?php
if (!function_exists('property_exists')) {
  function property_exists($class, $property) {
    if (is_object($class))
      $class = get_class($class);

    return array_key_exists($property, get_class_vars($class));
  }
}
?>