(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)
is_nan —Checks whether a float is NAN
Returns whether the givennum isNAN (Not A Number
).
NAN is returned from mathematical operations that are undefined, for example when passing parameters outside of function’s input domain. The square root (sqrt()) is only defined for positive numbers, passing a negative number will result inNAN. Other examples of operations returningNAN are dividingINF byINF and any operation involving an existingNAN value.
Note:
Despite its name of
Not A Number,NANis a valid value of typefloat.
numThefloat to check
Example #1is_nan() example
<?php
$nan=sqrt(-1);
var_dump($nan,is_nan($nan));
?>The above example will output:
float(NAN)bool(true)
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.I would use is_numeric() instead of ctype_digit() if you cannot be 100% sure what data type the string will be. Example from the docs:
<?php
$numeric_string='42';
$integer=42;
ctype_digit($numeric_string);// true
ctype_digit($integer);// false (ASCII 42 is the * character)
is_numeric($numeric_string);// true
is_numeric($integer);// true
?>Starting with PHP 7, the string 'NaN' evaluates to the NaN value as well.
Example:
var_dump( (float) 'NaN' );
PHP 5.x and HHVM:
float(0)
PHP 7.0:
float(NAN)