PHP empty()

PHP 中哪些情况是空的呢

The following things are considered to be empty:

“” (an empty string)

0 (0 as an integer)

0.0 (0 as a float)

“0” (0 as a string)

NULL

FALSE

array() (an empty array)

var $var; (a variable declared, but without a value in a class)

[code]$a = 0;
if (empty($a)){
    echo "a is empty";
}