What Does the & (ampersand) symbol mean in this circumstance?

Question

I'm new to php and mysql. Im following a tutorial from phpacademy on youtube. There is a section that is of form data, but everyone who followed the tutorial (myself included) got undefined index errors. I fixed it with & (ampersand) symbol. But what does it do in the follow circumstances?? Why does putting the & symbol in front of the $ stop the error? Is it the same as @ and is it just suppressing the error or did it actually fix it?

$submit = &$_POST['submit'];

Answer 1

It means instead of assigning the value to $submit, assign a reference to the value to $submit.

If you are familiar with C and pointers, it is like a pointer to the value that is automatically dereferenced when you access it. However, PHP doesn't allow things pointer arithmetic or getting the actual memory address (unlike C).

$a = 7;
$b = $a;
$c = &$a;
$c = 5;

echo $a, $b, $c; // 575

CodePad.

To stop the error you mentioned, you can use a pattern such as...

$submit = isset($_POST['submit']) ? $_POST['submit'] : 'default_value';

...or...

$submit = filter_input(INPUT_POST, 'submit');