is_infinite
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
(PHP 4 >= 4.2.0, PHP 5)
is_nan — Prüft ob ein Wert keine Zahl ist
Beschreibung
bool is_nan
( float
$val
)
Prüft ob der Parameter val keine darstellbare
Zahl ist, wie z.B. das Ergebnis von acos(1.01).
Parameter-Liste
-
val -
Der zu prüfende Wert
Rückgabewerte
Liefert TRUE wenn val keine darstellbare
Zahl ist, sonst FALSE.
Beispiele
Beispiel #1 is_nan()-Beispiel
<?php
// Undefinierte Berechnung liefert ein NaN-Ergebnis
$nan = acos(8);
var_dump($nan, is_nan($nan));
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
float(NAN) bool(true)
Siehe auch
- is_finite() - Prüft auf einen gültigen endlichen Wert
- is_infinite() - Prüft ob ein Wert unendlich ist
add a note
User Contributed Notes
is_nan - [7 notes]
darkangel at moveinmod dot net ¶
7 years ago
php at keith tyler dot com ¶
3 years ago
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.
modern dot apocalypse at gmail dot com ¶
1 year ago
I have decided to do some testing because I am getting unusual results with the is_nan function and here are the results of my tests:
<?php
var_dump(NAN); // float NAN
var_dump(NAN == NAN); // boolean true
var_dump(NAN === NAN); // boolean true
var_dump(is_nan(NAN)); // boolean true
var_dump(NAN == 12); // boolean true
var_dump(NAN === 12); // boolean false
var_dump(is_nan(12)); // boolean false
var_dump(NAN == 12.4); // boolean true
var_dump(NAN === 12.4); // boolean true
var_dump(is_nan(12.4)); // boolean false
var_dump(NAN == NULL); // boolean true
var_dump(NAN === NULL); // boolean false
var_dump(is_nan(NULL)); // boolean false
var_dump(NAN == 'K<WNPO'); // boolean true
var_dump(NAN === 'K<WNPO'); // boolean false
var_dump(is_nan('K<WNPO')); // null and throws a warning "Warning: is_nan() expects parameter 1 to be double, string given in NANTest.php on line 13"
Sku ¶
7 years ago
Hi nez,
better would be:
function isNaN( $var ) {
return !ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}
ys, Sku
nez [at] NOSPAM gazeta [dot] pl ¶
7 years ago
Paul, i guess better would be:
function isNaN( $var ) {
return ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}