PHP - Strings and Integers

Question

My site uses PHP to check if the value submitted by the user using the "get" method is a certain integer. The code is something along the lines of

if ($_GET['input']==2) { ... }

However I have recently discovered that if the user inputs something like 2a, 2two or even 2omdodonsos, it is still perceived as the value 2 by PHP. However if the user inputs 23eee, 23twenty or 23ofnofnonf, it is not perceived as 2. Why does this happen? Will using this code:

 if ($_GET['input']="2") { ... }

solve the problem?

Ja͢ck · Accepted Answer · 2013-01-22 13:03:03Z

2

You can (and should) use input filtering to weed out the bad input:

if (is_null($input = filter_input(INPUT_GET, 'input', FILTER_VALIDATE_INT, FILTER_NULL_ON_FAILURE))) {
    // an entry that was not an integer
} elseif ($input === 2) {
    // input was 2
}

1 Comment

Martin Lyne Over a year ago

PHPs filter functions are underused. Shame, they're good. Upvoted.

Fabian Schmengler · Accepted Answer · 2013-01-22 13:04:19Z

1

For an explanation why this happens, read the documentation on type juggling.

The solution is a type safe comparison (===)

$_GET['input'] === '2'

answered Jan 22, 2013 at 13:04

Fabian Schmengler

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2 Comments

Cobra_Fast Over a year ago

Additionally, (int)sprintf('%d', $_GET['input']) could make sure you're working with a clean number. It will return 0 if the input variable couldnt be parsed into a decimal number.

Fabian Schmengler Over a year ago

@Cobra_Fast: this should be functionally equivalent to intval($_GET['input']) or (int)$_GET['input']. The sprintf is redundant. Of course it only becomes relevant as soon as the input will be used in other places than the "equals 2" check.

Juan de Parras · Accepted Answer · 2013-01-22 13:47:22Z

0

You can check if the GET value is numeric and then compare it with number 2:

if (is_numeric($_GET['input']) ) {
    switch($_GET['input']) {
      case 1:
      case 2:
       // write your code here
      break;
      default:
       //Default option
     }
 }

OR use directly === comparison operator as @fab suggested.

http://php.net/manual/en/language.operators.comparison.php

edited Jan 22, 2013 at 13:47

answered Jan 22, 2013 at 13:04

Juan de Parras

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