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 ...
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