PHP CookBook

Recipe 2.2 Checking Whether a String Contains a Valid Number

2.2.1 Problem

You want to ensure that a string contains a number. For example, you want to validate an age that the user has typed into a form input field.

2.2.2 Solution

Use is_numeric( ):

if (is_numeric('five')) { /* false */ }

if (is_numeric(5))      { /* true  */ }
if (is_numeric('5'))    { /* true  */ }

if (is_numeric(-5))     { /* true  */ }
if (is_numeric('-5'))   { /* true  */ }

2.2.3 Discussion

Besides working on numbers, is_numeric( ) can also be applied to numeric strings. The distinction here is that the integer 5 and the string 5 technically aren't the same in PHP.^[2]

^[2] The most glaring example of this difference came during the transition from PHP 3 to PHP 4. In PHP 3, empty('0') returned false, but as of PHP 4, it returns true. On the other hand, empty(0) has always returned true and still does. (Actually, you need to call empty( ) on variables containing '0' and 0.) See the Introduction to Chapter 5 for details.

Helpfully, is_numeric( ) properly parses decimal numbers, such as 5.1; however, numbers with thousands separators, such as 5,100, cause is_numeric( ) to return false.

To strip the thousands separators from your number before calling is_numeric( ) use str_replace( ):

is_numeric(str_replace($number, ',', ''));

To check if your number is a specific type, there are a variety of self-explanatorily named related functions: is_bool( ) , is_float( ) (or is_double( ) or is_real( ); they're all the same), and is_int( ) (or is_integer( ) or is_long( )).

2.2.4 See Also

Documentation on is_numeric( ) at http://www.php.net/is-numeric and str_replace( ) at http://www.php.net/str-replace.