PHP intval() weird results

Question

I\'m encountering something weird and I don\'t know why it is happening!

I have a URL like:

http://mysite.com/users/USER_ID

this user id

Answer 1

PHP is a little odd when it comes to types.

Basically, what you are doing is parsing the string into a number (so 'abcdef' returns 0 because it isn't a number at all), then comparing the original string to the number.

Now, I can see why you would assume that it should be false, but PHP tries to be clever. Basically, == will coerce types, and almost always coerces to numbers if one of it's values is a number. So it is using the same conversion that you did on the string, then comparing.

It is a better idea to use === which also checks types.

Answer 2

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

Example       Name        Result

$a == $b      Equal       TRUE if $a is equal to $b after type juggling.

$a === $b     Identical   TRUE if $a is equal to $b,
                          and they are of the same type. 

Your string is casted to integer because of type juggling on == operator and intval() of a string returns 0

This explains why $id == $id_inted in your code evaluates to true.

If you make your test with === instead of == no type juggling will be performed.

Answer 3

PHP is really "wired" with so called type-juggling. It is the most error-prone part of most PHP-scripts. As such, you should always stay on the safe side and use the most robust check. For example intval("twelve") will return 0, which is a valid integer. But also considered "false": print if (intval("one")) ? "yup" : "nope" will print "nope".

In this case, using intval, in combination with a check if the integer is larger then zero, should do the trick:

<?php
$id = intval($_GET['id']);

if($id > 0){
  // The column which I should look into is id
  $column = 'id';
}else{
  // The column which I should look into is page_name
  $column = 'page_name';
}

$query = mysql_qyery(SELECT * FROM members WHERE $column = '$id');
?>

Or, shorter:

$id = intval($_GET['id']);

$column = ($id > 0) ? "id" : "page_name";
$query = mysql_qyery(SELECT * FROM members WHERE $column = '$id');

Aso note that $_GET["id"] might not be set, which would throw a notice in your code.

And last, but certainly not least: the SQL-injection: ?id=LittleBobby';Drop table users.

edit As commentor points out, there was a logical flaw in my code, stemming form the fact I tested it in phpsh only. I refactored it from using is_int() to intval and > 0. In a web-environment, $_GET["id"] is always a string; no matter what. Hence is_int() will always return FALSE.

Answer 4

To check if numeric value is requested, use is_numeric.

Answer 5

The integer value of var on success, or 0 on failure. Empty arrays return 0, non-empty arrays return 1. (From php.net intval().)

intval('abcdefg') will trigger an error and the function return with 0.