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(PHP 4 >= 4.2.0, PHP 5)
is_nan — Prüft ob ein Wert keine Zahl ist
Prüft ob der Parameter val keine darstellbare Zahl ist, wie z.B. das Ergebnis von acos(1.01).
Der zu prüfende Wert
Liefert TRUE wenn val keine darstellbare Zahl ist, sonst FALSE.
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)
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.
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.
Hi nez,
better would be:
function isNaN( $var ) {
return !ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}
ys, Sku
Paul, i guess better would be:
function isNaN( $var ) {
return ereg ("^[-]?[0-9]+([\.][0-9]+)?$", $var);
}
Since NaN is not even equal to itself, here is a way to test it:
<?php
function my_is_nan($_) {
return ($_ !== $_);
}
?>
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