66

I'm new to php and I have executed below code. 

<?php
class my_class{

    var $my_value = array();
    function my_class ($value){
        $this->my_value[] = $value;
    }
    function set_value ($value){
    // Error occurred from here as Undefined variable: my_value
        $this->$my_value = $value;

    }

}

$a = new my_class ('a');
$a->my_value[] = 'b';
$a->set_value ('c');
$a->my_class('d');

foreach ($a->my_value as &$value) {
    echo $value;
}

?>

I got below errors. What could be the error?

Notice: Undefined variable: my_value in C:\xampp\htdocs\MyTestPages\f.php on line 15

Fatal error: Cannot access empty property in C:\xampp\htdocs\MyTestPages\f.php on line 15
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1
  • 11
    If you're just learning PHP, look for some more up-to-date tutorials... the use of var and a method with the same name as the class indicate a pretty old, outdated tutorial Commented Feb 17, 2013 at 10:42

7 Answers 7

Reset to default
181

You access the property in the wrong way. With the $this->$my_value = .. syntax, you set the property with the name of the value in $my_value. What you want is $this->my_value = ..

$var = "my_value";
$this->$var = "test";

is the same as

$this->my_value = "test";

To fix a few things from your example, the code below is a better aproach

class my_class {

    public  $my_value = array();

    function __construct ($value) {
        $this->my_value[] = $value;
    }

    function set_value ($value) {
        if (!is_array($value)) {
            throw new Exception("Illegal argument");
        }

        $this->my_value = $value;
    }

    function add_value($value) {
        $this->my_value = $value;
    }
}

$a = new my_class ('a');
$a->my_value[] = 'b';
$a->add_value('c');
$a->set_value(array('d'));

This ensures, that my_value won't change it's type to string or something else when you call set_value. But you can still set the value of my_value direct, because it's public. The final step is, to make my_value private and only access my_value over getter/setter methods

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2 Comments

Then i'm getting error saying Fatal error: [] operator not supported for strings in C:\xampp\htdocs\MyTestPages\f.php on line 12. Line 12 is $this->my_value[] = $value;
Sure.. set_value change the type from my_value from array to string. Probably you want to change the code inside set_value to $this->my_value[] = $value;
32

First, don't declare variables using var, but

public $my_value;

Then you can access it using

$this->my_value;

and not

$this->$my_value;
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10

To access a variable in a class, you must use $this->myVar instead of $this->$myvar.

And, you should use access identifier to declare a variable instead of var.

Please read the doc here.

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2 Comments

Then i'm getting error saying Fatal error: [] operator not supported for strings in C:\xampp\htdocs\MyTestPages\f.php on line 12. Line 12 is $this->my_value[] = $value;
You can't call $this->my_value[] you should have a value in the [].
5

As I see in your code, it seems you are following an old documentation/tutorial about OOP in PHP based on PHP4 (OOP wasn't supported but adapted somehow to be used in a simple ways), since PHP5 an official support was added and the notation has been changed from what it was.

Please see this code review here:

<?php
class my_class{

    public $my_value = array();

    function __construct( $value ) { // the constructor name is __construct instead of the class name
        $this->my_value[] = $value;
    }
    function set_value ($value){
    // Error occurred from here as Undefined variable: my_value
        $this->my_value = $value; // remove the $ sign
    }

}

$a = new my_class ('a');
$a->my_value[] = 'b';
$a->set_value ('c'); // your array variable here will be replaced by a simple string 
// $a->my_class('d'); // you can call this if you mean calling the contructor 


// at this stage you can't loop on the variable since it have been replaced by a simple string ('c')
foreach ($a->my_value as &$value) { // look for foreach samples to know how to use it well
    echo $value;
}

?>

I hope it helps

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Comments

1

Interesting:

  1. You declared an array var $my_value = array();
  2. Pushed value into it $a->my_value[] = 'b';
  3. Assigned a string to variable. (so it is no more array) $a->set_value ('c');
  4. Tried to push a value into array, that does not exist anymore. (it's string) $a->my_class('d');

And your foreach wont work anymore.

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Comments

1

This way you can create a new object with a custom property name.

$my_property = 'foo';
$value = 'bar';
$a = (object) array($my_property => $value);

Now you can reach it like:

echo $a->foo;  //returns bar
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1 Comment

would have been more detailed..!
0

I realise this answer is not a direct response to the problem described by the OP, but I found this question as a result of searching for the same error message. I thought it worth posting my experience here just in case anybody is muddling over the same thing...

You can encounter the error in question as a result of a poorly formatted for loop over an associative array. In a fit of bone-headedness, I was using -> instead of => in my for statement:

        foreach ($object->someArray as $key->$val) {
            // do something
        }

Of course, I should have had:

        foreach ($object->someArray as $key=>$val) {
            // do something
        }

I confused myself at first, thinking the reported error was referring to the someArray property!

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