+--------------+-----------+---------+-----------+---------+--------+ | 真值表 | gettype() | empty() | is_null() | isset() | (bool) | +--------------+-----------+---------+-----------+---------+--------+ | $x = "" | string | true | false | true | false | | $x=null | NULL | true | true | false | false | | var $x | NULL | true | true | false | false | | $x = array() | array | true | false | true | false | | $x = false | boolean | true | false | true | false | | $x = 15 | integer | false | false | true | true | | $x = 1 | integer | false | false | true | true | | $x = 0 | integer | true | false | true | false | | $x = -1 | integer | false | false | true | true | | $x = '15' | string | false | false | true | true | | $x = '1' | string | false | false | true | true | | $x = '0' | string | true | false | true | false | | $x = '-1' | string | false | false | true | true | | $x = 'foo' | string | false | false | true | true | | $x = 'true' | string | false | false | true | true | | $x = 'false' | string | false | false | true | true | +--------------+-----------+---------+-----------+---------+--------+