Echoing a variable from a PHP class

Question

I had a quick look around at some of the similar questions to mine, but none of the answers quite touched on the problem I am having.

I have two files. product.php and index.php. Product.php defines the product class, and I'm just using index.php as a page to output the variables. Ideally, this would be used to output objects from different classes in the future.

product.php

class Product{
    public $var = "a default value";

    public function __construct($var){
        $var = $var;
    }

    public function displayVar(){
        echo $this->var;
    }
}

index.php (all enclosed in php tags obiously)

require_once("product.php");
$product = new Product();
echo $product->var;

I tried with different methods of including the file (require, include, include_once). I'm not sure if this is the issue.

The issue I'm getting is the $product->var doesn't output. Instead I get the following error:

Notice: Undefined property: Product::$var in C:\xampp\htdocs\FurnitureWebsite\index.php on line 21

I'm not entirely sure why it's considering this variable undefined. I looked through the PHP documentation on classes, and properties, but nothing that really looked like an answer.

A final note: I tried this with the class defined in index.php and it worked fine. This makes me think there might be something wrong with my file path, but the file name is spelt correctly, and the files are in the same directories, so I'm not totally sure.

a side note, there is no point in having a public getter displayVar to echo a public property. As it's public, you can access it directly. Or change the visibility of the property to protected or private if you want to restrict access to that property via an explicit getter. — John Joseph
– John Joseph, Commented Dec 21, 2016 at 11:05

Amin NAIRI · Accepted Answer · 2016-12-21 11:36:43Z

Explainations

First of all, in your class, you specified a variable for you constructor. But, this variable is mandatory (meaning, there is no default value). So when instanciating a new Product, you have to give a value.

Also, if you're using a constructor, there is no need to give the variable a default value before the call to the constructor.

That said, if you want to access to your value without calling a method on it, there is plenty of solutions.

Solution 1: instanciation and direct call to the variable

class Product {

    public $var = 'a default value';

}

$product = new Product();

echo $product->var;

Solution 2: using an accessor to get the protected/private value

class Product {

    protected $var = 'a default value';

    public function getVar() {

        return $this->var;

    }

}

$product = new Product();

echo $product->getVar();

Solution 3: using the constructor to initialize the value

class Product {

    protected $var;

    public function __construct($var = 'a default value') {

        $this->var = $var;

        /* $this->var stands for protected $var */

        /* $var stands for... $var in the parameters */

    }

    public function getVar() {

        return $this->var;

    }

}

$product = new Product(); /* no value, so $var = 'a default value'; */

echo $product->getVar();

Solution 4: using a static variable

class Product {

    public static $var = 'a default value';

}

echo Product::$var;

Solution 5: using a static method with a protected static value

class Product {

    protected static $var = 'a default value';

    public static function getVar() {

        return self::$var;

    }

}

echo Product::getVar();

Documentation

PHP : classes and objects.

PHP : visibility.

PHP : static.

PHP : constructors and destructors.

brtsos · Accepted Answer · 2016-12-21 11:04:25Z

1

class Product{
    public $var = "a default value";

    public function __construct($var){
        $this->var = $var;
    }

    public function displayVar(){
        return $this->var;
    }
}

require_once("product.php");
$product = new Product('Product Name');
echo $product->displayVar();

answered Dec 21, 2016 at 11:04

brtsos

3713 silver badges14 bronze badges

Comments

JustOnUnderMillions · Accepted Answer · 2016-12-21 11:09:50Z

1

class Product{
    protected $var;

    public function __construct($var = "a default value"){
        $this->var = $var;
    }

    public function getVar(){
        return $this->var;
    }
}

$product = new Product();
echo $product->getVar();

You have to give an value on new Product('your value'), your example has no value that is given to the constructor
Bind it right, not $var=$var do $this->var=$var
Set default value in __construct($var = "a default value"), better than directly at the property
Make the Variable protected not public else no getter is needed and the variable can changed from outside directly
create an getter for the variable, that returns the value, not echo it.

Thats it.

answered Dec 21, 2016 at 11:09

JustOnUnderMillions

3,80511 silver badges14 bronze badges

Comments

TomaszCyrulik · Accepted Answer · 2016-12-21 11:24:51Z

In your constructor you have this:

    public function __construct($var){
       $var = $var;
    }

Change it to:

    public function __construct($var){
       $this->var = $var;
    }

currently it just sets the passed variable to itself.

Second thing is that in your index.php file you create an object like this:

$product = new Product();

since your constructor expects some variable to get, you should always provide such. For example:

$product = new Product('new text');

I can see that you have a method to display a variable. That's good, although a common thing is to create such variable as protected and then creating a public getter method to access protected variables from outside the class. Then you can either simply call your method from index.php file like this:

$product->displayVar();

or create the getter method that will return your variable and display it in index.php file. eg.

/**product.php**/
public function getVariable() {
   return $this->var;
}


/**index.php**/
$product = new Product('new text');
echo $product->getVariable();

It depends on whether you will only need to display this variable or you know, that you will need this variable for other things. Either way, I think that creating the getter is better also because of a good habit.

I hope it helps. Good luck!

Dariusz Dusza · Accepted Answer · 2016-12-21 11:04:52Z

0

you have

public function __construct($var){
    $var = $var;
}

should be:

public function __construct($var){
    $this->var = $var;
}

answered Dec 21, 2016 at 11:04

Dariusz Dusza

175 bronze badges

Comments

Tonmoy Nandy · Accepted Answer · 2016-12-22 05:57:15Z

0

Please modify your code like this

Product.php

<?php class Product{
    public $var ;
    public function __construct($var){
            $this->var = $var;
    } } ?>

index.php

<?php require_once 'product.php';
     $product = new Product('a default value');
     echo $product->var; ?>

It's may help you.

Thanks

edited Dec 22, 2016 at 5:57

answered Dec 21, 2016 at 11:40

Tonmoy Nandy

3814 silver badges9 bronze badges

Collectives™ on Stack Overflow

Echoing a variable from a PHP class

6 Answers 6

Explainations

Solution 1: instanciation and direct call to the variable

Solution 2: using an accessor to get the protected/private value

Solution 3: using the constructor to initialize the value

Solution 4: using a static variable

Solution 5: using a static method with a protected static value

Documentation

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Collectives™ on Stack Overflow

6 Answers 6

Explainations

Solution 1: instanciation and direct call to the variable

Solution 2: using an accessor to get the protected/private value

Solution 3: using the constructor to initialize the value

Solution 4: using a static variable

Solution 5: using a static method with a protected static value

Documentation

Comments

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