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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Коментарии
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($integer); // true
?>
Starting with PHP 7, the string 'NaN' evaluates to the NaN value as well.
Example:
var_dump( (float) 'NaN' );
PHP 5.x and HHVM:
float(0)
PHP 7.0:
float(NAN)
function is_nan2($n) {
return $n !== $n;
}
is_nan2(NAN); // true