PHP数据类型，真与假？
1.所有的资源类型，都是真？
2.NULL类型，都是假？
回复讨论(解决方案)
所有的空值都视为“假”:0,'0','',false,null,array()....
反之则视为“真”
当转换为 boolean 时，以下值被认为是 FALSE：
布尔值 FALSE 本身
整型值 0（零）
浮点型值 0.0（零）
空字符串，以及字符串 "0"
不包括任何元素的数组
不包括任何成员变量的对象（仅 PHP 4.0 适用）
特殊类型 NULL（包括尚未赋值的变量）
从没有任何标记（tags）的 XML 文档生成的 SimpleXML 对象
所有其它值都被认为是 TRUE（ 包括任何资源）。
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