Validating an integer with PHP

When I started writing this post I wasn’t sure should I put this into programming category or fun … I mean, validating if passed variable is integer aka whole number, how hard can it be? It appears not really easy in PHP :)

First off some background, I needed to validate an array with db key values (like array(1,2,6,7,…n)), so I thought of using simple function like array_filter with callback, something like:

array_filter($foo_array, 'is_int');

where is_int is callback, calling built in is_int function for each array value in order to filter out non int values.

The problem is (yes after 10 years dealing with PHP I am aware of that), PHP doesn’t treat int and string numbers the same, so string ’42’ wouldn’t be recognized as integer.

is_int('42'); //false
is_int(42); //true

To make things more “interesting” for programmers, if you have integer form data like age, year or whatever, they will be sent trough $_POST/$_GET/$_REQUEST arrays as ‘string numbers’ (so string ’42’ not int 42).

There is nice function to deal with such things and it’s name is is_numeric … but it only checks if string is actually number, so float values will be evaluated to true as well. ctype_digit on the other hand is opposite of is_int, it will only return true if test variable is string number, so ’42’ would evaluate to true, but 42 to false.

ctype_digit('42'); //true

And to make things even worse, PHP is silently converting really big integers to float (those bigger than PHP_INT_MAX const) so guess what would you get for number like is_int(23234234234235334234234)? Yep, false :)

$var = PHP_INT_MAX;
var_dump($var++); //true
var_dump($var); //false it's float now!

Yeah I know, you could cast var to int and do is_int … or cast var to string and do ctype_digit … and other dirty hacks… but what if someone smart from PHP team had decided to let say add 2nd argument to is_int check so you can check for type in some kind of ‘non strict’ mode, so string ’42’ is actually evaluated as integer? Something like this in C I guess:

function is_int(int var, int strict = 1)
   //if strict is false evaluate string integers like '42' to true!

All in all (at least to me), the easiest way to validate whether a variable is whole number (aka string or integer string) is with regular expression. Something like this:

 * Test if number is integer, including string integers
 * @param mixed var
 * @return boolean
function isWholeNumber($var)
	if(preg_match('/^\d+$/', $var))
		return true;
		return false;

Someone from PHP dev team should really consider fixing this.


  1. October 20th, 2011 | 9:44 am

    PHP is a failure on so many levels that it’s inappropriate to comment on it anymore.

    I’ll just say that I blame PHP for giving all dynamically typed languages a bad name.

  2. svlada
    May 29th, 2012 | 7:04 pm

    Is there any reason not to use “is_numeric” function?

  3. svlada
    May 29th, 2012 | 7:12 pm

    Skipped part where you are mentioned is_numeric :)

  4. Levi
    December 10th, 2012 | 10:03 pm

    You still don’t know about `filter_var` and `FILTER_VALIDATE_INT`?

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