PHP - Use isset inside function not working..?

Question

I have a PHP script that when loaded, check first if it was loaded via a POST, if not if GET['id'] is a number.

Now I know I could do this like this:

if(isset($_GET['id']) AND isNum($_GET['id'])) { ... }

function isNum($data) {  
    $data = sanitize($data);
    if ( ctype_digit($data) ) {
        return true;
    } else {
        return false;
    }
}

But I would like to do it this way:

if(isNum($_GET['id'])) { ... }

function isNum($data) {  
    if ( isset($data) ) {
        $data = sanitize($data);
        if ( ctype_digit($data) ) {
            return true;
        } else {
            return false;
        }
    } else {
        return false;
    }
}

When I try it this way, if $_GET['id'] isn't set, I get a warning of undefined index: id... It's like as soon as I put my $_GET['id'] within my function call, it sends a warning... Even though my function will check if that var is set or not...

Is there another way to do what I want to do, or am I forced to always check isset then add my other requirements..??

Answer 1

You're referencing an undefined index while passing it initially. You could do this:

$key = 'id';

function foo($id ) {
    if ( isset( $_GET[$id] ) ) { 
    }
}

Alternatively you could just do isset before the function call.

if ( isset($_GET['id']) && isNum($_GET['id'])) { }

Another option, use a temporary variable:

$foo = isset( $_GET['id'] ) ? $_GET['id'] : null;
if ( $foo ) { functionCall($foo); }

You can also tone down the error reporting levels if it doesn't concern you that much.

Answer 2

I always include a convenience function that a few other languages provide: get.

function get($needle, $haystack, $return=null) {
    return array_key_exists($needle, $haystack) ? $haystack[$needle] : $return;
}

Now you can call:

if(isNum(get('id', $_GET))) {
    // do something here
}

Answer 3

Here is an elegant way of doing it using a custom class:

First, define a SmartArray class:

class SmartArray extends ArrayObject {
    public static function convert(&$array) {
        $array = new self($array);
    }
    public function offsetGet($index) {
        return $this->offsetExists($index)? parent::offsetGet($index):NULL;
    }
}

Then simply call:

SmartArray::convert($_GET);

Now your if(isNum($_GET['id'])) { ... } won't complain anymore if $_GET doesn't have the key 'id' :)

Answer 4

You can change isNum to receive the parameter by reference

<?php

if(isNum($_GET['id'])) { ... }

function isNum(&$data) {
    if (isset($data) ) {
        $data = sanitize($data);
        return ctype_digit($data);
    } else {
        return false;
    }
}

However, $_GET['id'] will be implicitly created on call and initialized to NULL.

If you're not OK with that or with the hacky nature of this solution, go with some other answer.