php怎么将数值转换为布尔类型

<?php
var_dump(!!2);  //返回true
var_dump(!!0);  //返回false
var_dump(!!1);  //返回true
?>

<?php
var_dump((bool)2);  //返回true
var_dump((bool)0);  //返回false
var_dump((bool)1);  //返回true
var_dump((bool)100);  //返回true
?>

<?php
echo &#39;0:        &#39;.(boolval(0) ? &#39;true&#39; : &#39;false&#39;)."<br>";
echo &#39;42:       &#39;.(boolval(42) ? &#39;true&#39; : &#39;false&#39;)."<br>";
echo &#39;0.0:      &#39;.(boolval(0.0) ? &#39;true&#39; : &#39;false&#39;)."<br>";
echo &#39;4.2:      &#39;.(boolval(4.2) ? &#39;true&#39; : &#39;false&#39;)."<br>";
echo &#39;"0":      &#39;.(boolval("0") ? &#39;true&#39; : &#39;false&#39;)."<br>";
echo &#39;"1":      &#39;.(boolval("1") ? &#39;true&#39; : &#39;false&#39;)."<br>";
?>

0:        false
42:       true
0.0:      false
4.2:      true
"0":      false
"1":      true