PHP Cookbook

2.1. Checking Whether a String Contains a Valid Number

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.

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  */ }

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]

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( ) ).

See Also

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

^[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 ...