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php unset()详解

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Jun 23, 2016 pm 02:35 PM

简介：这是php unset()详解的详细页面，介绍了和php,unset, php php unset()详解有关的知识、技巧、经验，和一些php源码等。

class='pingjiaF' frameborder='0' src='http://biancheng.dnbcw.info/pingjia.php?id=361000' scrolling='no'> 1.如果有多个变量名指向某一个变量值,unset任何一个变量名只是断开变量名和变量值之间的关系,不会释放内存,该值还存在
   (例外见2).
2.两种情况会释放内存,否则内存中该变量值还存在.
   a)该变量值占用空间超过256字节的时候用unset()才会释放内存(这是有人的测试结果,待解释)
   b)当指向该值的所有变量（比如有引用变量指向该值）都被销毁后
3.如果想释放变量内存,最好用$a=NULL释放,当赋于NULL值时,该地址被释放,所有指向该变量值的引用都为空了
4.当在局部环境unset全局变量时,该全局变量只是在局部作用域失效.在其他地方不变

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