从常量类文件中访问常量

Question

    class Constants
    {
            public static $url1      = "http=//url1";
            public static $url2       = Constants::$url1."/abc";
    }

I want to access constant from with in a class but i am not able yo do it. How can i do it ?

Answer 1

Instead of using Constants:: you should use self:: to access class variables. For example:

public static $url2 = self::$url1 . "/abc";

Answer 2

This is not a constant. This is a static property.

You also cannot use self as value:

public static $url2 = self::$url1."/abc"; // will throw error

You have to initialize in constructor:

class Constants
{
    public static $url1 = "http=//url1";
    public static $url2;

    public function __construct(){
        self::$url2 = self::$url1."/abc";
    }
}

$const = new Constants();
echo $const::$url2;
//or if the class is initialized
echo Constants::$url2;

The other option would be to make a static method:

class Constants
{
    public static $url1 = "http=//url1";        

    public static function getUrl2(){
        return self::$url1."/abc";
    }
}

echo Constants::getUrl2();

Answer 3

Just see Below Codes.

From outside the class definition

    <?php
    class MyClass {
        const CONST_VALUE = 'A constant value';
    }

    $classname = 'MyClass';
    echo $classname::CONST_VALUE; // As of PHP 5.3.0

    echo MyClass::CONST_VALUE;
    ?>

From inside the class definition

    <?php
    class OtherClass extends MyClass
    {
        public static $my_static = 'static var';

        public static function doubleColon() {
            echo parent::CONST_VALUE . "\n";
            echo self::$my_static . "\n";
        }
    }

    $classname = 'OtherClass';
    echo $classname::doubleColon(); // As of PHP 5.3.0

    OtherClass::doubleColon();
    ?>