(PHP 4 >= 4.2.0, PHP 5, PHP 7)

is_infiniteFinds whether a value is infinite


bool is_infinite ( float $val )

Returns TRUE if val is infinite (positive or negative), like the result of log(0) or any value too big to fit into a float on this platform.



The value to check

Return Values

TRUE if val is infinite, else FALSE.

See Also

  • is_finite() - Finds whether a value is a legal finite number
  • is_nan() - Finds whether a value is not a number

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User Contributed Notes 5 notes

13 years ago
If you have PHP lower than 4.2 you can simulate the behaviour:

function is_infinite($value) {
   return (substr("$value",-3) == "INF");

(tested on php 4.1.2)
stangelanda at arrowquick dot com
10 years ago
Actually any string ending in INF is more appropriate than any string beginning with INF.  Since negative infinity evaluates to "-INF" but it is still infinite.  However in either case the STRING "INF" is not infinite, only a float that converts to "INF" or "-INF" is infinite.

A more appropriate function might be:
if (!is_defined('is_infinite')) { function is_infinite($val) {
    return (
is_float($val) and ("$val"=='INF' or "$val"=='-INF'));
} }
* However the above function is untested.
11 years ago
@ david,

That will return true for any string ending with "INF".
I think substr("$value",0,3) would be more appropriate.
espertalhao04 at hotmail dot com
4 years ago
fastest version to php <4.2:
<?php function is_infinite($v){$v=$v>>0;return -9e1000==$v||$v==9e1000;}; ?>

the $v=$v>>0; is just to ensure it is a number and its not mandatory.
effectively, the function can be reduced to:
<?php function is_infinite($v){return -9e1000==$v||$v==9e1000;}; ?>

this works because any number that is too big or too small for a float is considered to be infinite or -infinite.
5 years ago
PHP_INT_MAX is The largest integer supported in this build of PHP. Usually int(2147483647). Available since PHP 4.4.0 and PHP 5.0.5
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