is_infinite
It seems odd to me, but in boolean context, NAN evalutes to true.
<?php
var_dump(acos(8));
var_dump((bool)acos(8));
?>
Returns:
float(NAN)
bool(true)
Incidentally INF and -INF also evaluate to true.
is_nan
(PHP 4 >= 4.2.0, PHP 5)
is_nan — Finds whether a value is not a number
Description
bool is_nan
( float $val
)
Checks whether val is 'not a number', like the result of acos(1.01).
Parameters
- val
-
The value to check
Return Values
Returns TRUE if val is 'not a number', else FALSE.
Examples
Example #1 is_nan() example
<?php
// Invalid calculation, will return a
// NaN value
$nan = acos(8);
var_dump($nan, is_nan($nan));
?>
The above example will output:
float(NAN) bool(true)
See Also
- is_finite() - Finds whether a value is a legal finite number
- is_infinite() - Finds whether a value is infinite
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User Contributed Notes
is_nan
php at keith tyler dot com
14-Apr-2010 10:46
J.K.
07-Jul-2009 10:44
For seeing whether or not something is a number, use ctype_digit().
darkangel at moveinmod dot net
01-Mar-2006 03:04
nan/"not a number" is not meant to see if the data type is numeric/textual/etc..
NaN is actually a set of values which can be stored in floating-point variables, but dont actually evaluate to a proper floating point number.
The floating point system has three sections: 1 bit for the sign (+/-), an 8 bit exponent, and a 23 bit fractional part.
There are rules governing which combinations of values can be placed into each section, and some values are reserved for numbers such as infinity. This leads to certain combinations being invalid, or in other words, not a number.
Sku
03-Dec-2005 06:29
Hi nez,
better would be:
function isNaN( $var ) {
return !ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}
ys, Sku
nez [at] NOSPAM gazeta [dot] pl
26-Sep-2005 07:27
Paul, i guess better would be:
function isNaN( $var ) {
return ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}
Vincent
23-Feb-2005 11:04
Since NaN is not even equal to itself, here is a way to test it:
<?php
function my_is_nan($_) {
return ($_ !== $_);
}
?>