PHP - Private class variables giving error: undefined variable

Question

I am getting the error "Undefined variable: interval in C:\wamp\www\DGC\classes\DateFilter.php"

Here is my code for the DateFilter class:

class DateFilter extends Filter
{
    //@param daysOld: how many days can be passed to be included in filter
    //Ex. If daysOld = 7, everything that is less than a week old is included
    private $interval;

    public function DateFilter($daysOld)
    {
        echo 'days old' . $daysOld .'</ br>';
        $interval = new DateInterval('P'.$daysOld.'D');
    }


    function test()
    {
        echo $interval->format("%d days old </br>");
        //echo 'bla';
    }

}

When I create a new instance of the DateFilter class and call test() it give me the error. I realize it means the variable hasn't been initialized, but I know that the constructor is being called because I put an echo statement in there and it was output.

I have also tried: $this::$interval->format(...); self::$interval->format(...); but it didn't work.

I know this is probably an easy fix, sorry for the noob question. Can't believe this stumped me.

Jonathon Reinhart · Accepted Answer · 2011-10-12 23:09:46Z

44

You have to use $this->interval to access the member variable interval in PHP. See PHP: The Basics

class DateFilter extends Filter
{
    private $interval;    // this is correct.

    public function DateFilter($daysOld)
    {
        $this->interval = new DateInterval('P'.$daysOld.'D');   // fix this
    }

    function test()
    {
        echo $this->interval->format("%d days old </br>");     // and fix this
    }
}

edited Oct 12, 2011 at 23:09

answered Oct 12, 2011 at 22:45

Jonathon Reinhart

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6 Comments

CHawk Over a year ago

echo $this->$interval->format("%d days old </br>"); Is also giving me this same error :/

Jonathon Reinhart Over a year ago

remove the second dollar sign. It's $this->interval

gremo Over a year ago

I've always find quite "strange" that PHP forces you to use $this to access object fields. Many other languages such as C# will not (if the variable has not the same name of a local one). Anyway the use of this is always a good practice, IMHO: it helps you to quick look at object properties and avoid confusion with local variables.

Jonathon Reinhart Over a year ago

Definitely. Python has the same requirement (with 'self.' although 'self' is just a convention, and you have to actually provide a 'self' parameter in a function). I don't mind, because it makes sure you know what you're actually referencing. Quite important in these dynamic languages when you can declare stuff all over the place.

CHawk Over a year ago

Thank you for the help! I am use to languages where the this is optional. Anyways, when I take away the 2nd dollar sign, I get this error: Fatal error: Call to a member function format() on a non-object

|

Herbert · Accepted Answer · 2011-10-12 22:57:43Z

4

$interval is local to the function. $this->interval references your private property.

class DateFilter extends Filter
{
    //@param daysOld: how many days can be passed to be included in filter
    //Ex. If daysOld = 7, everything that is less than a week old is included
    private $interval;

    public function DateFilter($daysOld)
    {
        echo 'days old' . $daysOld .'</ br>';
        $this->interval = new DateInterval('P'.$daysOld.'D');
    }


    function test()
    {
        echo $this->interval->format("%d days old </br>");
        //echo 'bla';
    }

}

answered Oct 12, 2011 at 22:57

Herbert

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1 Comment

CHawk Over a year ago

Perfect, that was the last piece of the puzzle I was missing.

CheeseSucker · Accepted Answer · 2011-10-12 22:46:13Z

2

function test()
{
    echo $this->interval->format("%d days old </br>");
}

answered Oct 12, 2011 at 22:46

CheeseSucker

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Comments

Jan Wiemers · Accepted Answer · 2011-10-12 22:53:11Z

0

trying

public var $interval;

and

echo $this->interval;

answered Oct 12, 2011 at 22:53

Jan Wiemers

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