[php] PHP is_numeric or preg_match 0-9 validation

This isn't a big issue for me (as far as I'm aware), it's more of something that's interested me. But what is the main difference, if any, of using is_numeric over preg_match (or vice versa) to validate user input values.

Example One:

<?php
    $id = $_GET['id'];
    if (!preg_match('/^[0-9]*$/', $id)) {
        // Error
    } else {
        // Continue
    }
?>

Example Two:

<?php
    $id = $_GET['id'];
    if (!is_numeric($id)) {
        // Error
    } else {
        // Continue
    }
?>

I assume both do exactly the same but is there any specific differences which could cause problems later somehow? Is there a "best way" or something I'm not seeing which makes them different.

is_numeric would accept "-0.5e+12" as a valid ID.

If you're only checking if it's a number, is_numeric() is much much better here. It's more readable and a bit quicker than regex.

The issue with your regex here is that it won't allow decimal values, so essentially you've just written is_int() in regex. Regular expressions should only be used when there is a non-standard data format in your input; PHP has plenty of built in validation functions, even an email validator without regex.

According to http://www.php.net/manual/en/function.is-numeric.php, is_numeric alows something like "+0123.45e6" or "0xFF". I think this not what you expect.

preg_match can be slow, and you can have something like 0000 or 0051.

I prefer using ctype_digit (works only with strings, it's ok with $_GET).

<?php
  $id = $_GET['id'];
  if (ctype_digit($id)) {
      echo 'ok';
  } else {
      echo 'nok';
  }
?>

Not exactly the same.

From the PHP docs of is_numeric:

'42' is numeric
'1337' is numeric
'1e4' is numeric
'not numeric' is NOT numeric
'Array' is NOT numeric
'9.1' is numeric

With your regex you only check for 'basic' numeric values.

Also is_numeric() should be faster.

is_numeric() allows any form of number. so 1, 3.14159265, 2.71828e10 are all "numeric", while your regex boils down to the equivalent of is_int()

is_numeric checks whether it is any sort of number, while your regex checks whether it is an integer, possibly with leading 0s. For an id, stored as an integer, it is quite likely that we will want to not have leading 0s. Following Spudley's answer, we can do:

/^[1-9][0-9]*$/

However, as Spudley notes, the resulting string may be too large to be stored as a 32-bit or 64-bit integer value. The maximum value of an signed 32-bit integer is 2,147,483,647 (10 digits), and the maximum value of an signed 64-bit integer is 9,223,372,036,854,775,807 (19 digits). However, many 10 and 19 digit integers are larger than the maximum 32-bit and 64-bit integers respectively. A simple regex-only solution would be:

/^[1-9][0-9]{0-8}$/ 

or

/^[1-9][0-9]{0-17}$/

respectively, but these "solutions" unhappily restrict each to 9 and 19 digit integers; hardly a satisfying result. A better solution might be something like:

$expr = '/^[1-9][0-9]*$/';
if (preg_match($expr, $id) && filter_var($id, FILTER_VALIDATE_INT)) {
    echo 'ok';
} else {
    echo 'nok';
}

is_numeric checks more:

Finds whether the given variable is numeric. Numeric strings consist of optional sign, any number of digits, optional decimal part and optional exponential part. Thus +0123.45e6 is a valid numeric value. Hexadecimal notation (0xFF) is allowed too but only without sign, decimal and exponential part.

You can use this code for number validation:

if (!preg_match("/^[0-9]+$/i", $phone)) {
        $errorMSG = 'Invalid Number!';
        $error    = 1;
    }

Meanwhile, all the values above will only restrict the values to integer, so i use

/^[1-9][0-9\.]{0,15}$/

to allow float values too.

PHP's is_numeric function allows for floats as well as integers. At the same time, the is_int function is too strict if you want to validate form data (strings only). Therefore, you had usually best use regular expressions for this.

Strictly speaking, integers are whole numbers positive and negative, and also including zero. Here is a regular expression for this:

/^0$|^[-]?[1-9][0-9]*$/

OR, if you want to allow leading zeros:

/^[-]?[0]|[1-9][0-9]$/

Note that this will allow for values such as -0000, which does not cause problems in PHP, however. (MySQL will also cast such values as 0.)

You may also want to confine the length of your integer for considerations of 32/64-bit PHP platform features and/or database compatibility. For instance, to limit the length of your integer to 9 digits (excluding the optional - sign), you could use:

/^0$|^[-]?[1-9][0-9]{0,8}$/