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PHP变量引用的疑惑
本以为自己对变量的引用和赋值已经很清楚,结果遇到了下面这个问题,彻底颠覆了我的理解

<br /><?php <br />  $str = 'WangChuanbo';<br />  $s = &$str;<br />  unset($str);<br />  echo $s,'hello world';<br />?>

结果$s输出后还是Wangchuanbo,不是同一块内存地址吗,原变量都被卸载了,引用变量还有值??

php 变量引用
------解决方案--------------------
张飞姓张名飞字翼德
即 张飞 和 张翼德 是同一个人
你把张飞杀了,只是把张飞这个名字重世间抹去,而那个人还在以张翼德这个称谓到处游逛
------解决方案--------------------
unset一个引用,只是断开了变量名和变量内容之间的绑定
$s = &$str;在php中的意思是
$s和$str都指向同一个地方C
unset之后$str就找不到C了
我再给你举个例子
小张听小李说财宝在大海上
小李失忆了,但小张还是知道财宝在海上

而在C++中,引用就意味着连内存地址都相同
说到底就是个常量指针
------解决方案--------------------
简单的说
C的指针 指向的是内存中特定的地址
C的指针 有个数据类型的概念,因此指针是可以参与运算的
php代码并没有给编译成机器码,所以没就访问内存地址一说
的确php的引用机制和C的指针极其相似,如果不计指针的运算,那么至少在表现上与指针是一样的

------解决方案--------------------
首先你得理解PHP的垃圾回收机制,你unset掉一个变量并不是从内存中给抹除了!PHP的垃圾回收是GC来完成的!
------解决方案--------------------
顶贴收藏~~


------解决方案--------------------
引用:
引用:unset一个引用,只是断开了变量名和变量内容之间的绑定
$s = &$str;在php中的意思是
而在C++中,引用就意味着连内存地址都相同
……

那当然了,如果你非要这么理解的话,呵呵
你在F盘有个文件夹fff,右健"发送到=〉桌面快捷方式"
然后改名叫aaa,再操作一次,改名叫bbb
打开aaa建个txt在里面,再打开bbb里面也有txt了
不就是这回事嘛


------解决方案--------------------
6楼说的对 要理解这个你需要理解PHP的垃圾回收机制  

PHP 的变量并不像C/C++一样  PHP的变量存储在ZVAL机构中 结构体定义如下
typedef struct _zval_struct zval;
...
struct _zval_struct { 
   /* Variable information */
    zvalue_value value;     /* value */
    zend_uint refcount__gc;    
    zend_uchar type;    /* active type */
    zend_uchar is_ref__gc;
};
zval结构体中有四个字段,其含义分别为:

属性名 含义 默认值 
refcount__gc 表示引用计数 1 
is_ref__gc 表示是否为引用 0 
value 存储变量的值  
type 变量具体的类型 

unset() 并不会直接销毁变量 只有当refcount=0时才会被PHP的垃圾回收机制回收

$a = 10;
xdebug_debug_zval('a'); 
//output: a: (refcount=1, is_ref=0)=10
$b = &$a;
xdebug_debug_zval('a'); 
//output: a: (refcount=2, is_ref=1)=10
$a = 20;
xdebug_debug_zval('a'); 
//output: a: (refcount=2, is_ref=1)=20
unset($b);
xdebug_debug_zval('a'); 
//output: a: (refcount=1, is_ref=0)=20



------解决方案--------------------
其实很多人在解释引用时都喜欢那php的底层实现来说事,其实这是不对的
解释要用浅显的道理,而非深层次的原理来说明。否则就是越说越乱
就像任何 C 语言书中都不会用汇编语言来解释指针,因为高层都还没明白,底层怎么能明白

php 的引用从表现上看,就如同指针一样。所以把它看成“指针”并无大碍
只是你不要把引用当做“指针”来运算就可以了

换一种方式来理解的话就是
指针是按门牌号码来进出商业街上的每家店铺,所以他可以明确的知道下一家在哪里
引用是按店铺的招牌来进出的,因此他并不能知道旁边的是谁
除此之外,两者的表现并无区别
------解决方案--------------------
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