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.
is_nan
说明
bool is_nan ( float val )如果 val 为“非数值”，例如 acos(1.01) 的结果，则返回 TRUE。
参见 is_finite() 和 is_infinite()。
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User Contributed Notes
darkangel at moveinmod dot net
02-Mar-2006 02:04
02-Mar-2006 02:04
Sku
04-Dec-2005 05:29
04-Dec-2005 05:29
Hi nez,
better would be:
function isNaN( $var ) {
return !ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}
ys, Sku
nez [at] NOSPAM gazeta [dot] pl
27-Sep-2005 04:27
27-Sep-2005 04:27
Paul, i guess better would be:
function isNaN( $var ) {
return ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}
Vincent
24-Feb-2005 10:04
24-Feb-2005 10:04
Since NaN is not even equal to itself, here is a way to test it:
<?php
function my_is_nan($_) {
return ($_ !== $_);
}
?>
paul at NOSPAM dot paultastic dot com
11-Jun-2002 02:55
11-Jun-2002 02:55
See is_numeric if you have an older version of PHP than 4.20. It should serve your purpose well.
If you're using PHP 3, you can use a regular expression:
function isNaN( $var ) {
return ereg ("^[0-9\.]+$", $var);
}