php新手,问个手册里面实例代码的有关问题
php新手,问个手册里面实例代码的问题
对最后一行的结果有点疑惑,$assigned=$instance,这句不是拷贝吗,那这两个对象应该是两个内容相同但地址不同的对象,在拷贝后的赋值$instance->var = '$assigned will have this value';为什么会影响到$assigned??
------解决思路----------------------
所谓值传递,就是说仅将对象的值传递给目标对象,就相当于copy;系统将为目标对象重新开辟一个完全相同的内存空间。
所谓引用,就是说将对象在内存中的地址传递给目标对象,就相当于使目标对象和原始对象对应同一个内存存储空间。此时,如果对目标对象进行修改,内存中的数据也会改变。
值传递和引用的区别
------解决思路----------------------
我的理解:
<br />class SimpleClass{<br /> var $test='test';<br />}<br /><br />//对象实例 分配内存地址为 1<br />$instance = new SimpleClass();<br />var_dump($instance);<br /><br />//复制对象实例的值 存入内存地址 2 存入的是SimpleClass类返回的同一个标识符的拷贝<br />//$instance = $assigned = new时返回的一个标识符id<br />$assigned = $instance;<br />var_dump($assigned);<br /><br />//引用传递 $reference 指向内存地址为 1<br />$reference = &$instance;<br />var_dump($reference);<br /><br />//改变了内存地址 1 <br />$instance->test= 'modify';<br />//因为是地址引用 所以$reference 也为null<br />$instance = null;<br />
手册说明:在php5,一个对象变量已经不再保存整个对象的值。只是保存一个标识符来访问真正的对象内容。 当对象作为参数传递,作为结果返回,或者赋值给另外一个变量,另外一个变量跟原来的不是引用的关系,只是他们都保存着同一个标识符的拷贝,这个标识符指向同一个对象的真正内容。
------解决思路----------------------
你的代码过于陈旧,说明也没到位
$instance 是对象。从 php5 开始,对象都是以引用方式传递的
所以 $assigned = $instance, 后
$assigned 和 $instance 指向同一个对象,一个的属性发生变化,另一个就跟着变

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