Underflow¶

Underflow happens when a value goes below a limit: out of its range of existence, the behavior of the value is now unknown.

Underflow happens with integers (limited to PHP_INT_MAX and PHP_INT_MIN), floats (PHP_FLOAT_MAX and PHP_FLOAT_MIN).

Other situations, such as accessing an array element or a string character beyond its first element, defaults to returning null.

<?php

    $a = PHP_INT_MAX;
    $b = (int) ($a +  1);

    echo $a.PHP_EOL;
    echo $b;

?>