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有些时候使用变化变量是十分方便的。也就是说,一个变量的名字将被动态的设置和使用。一个普通的变量将会使用如下的申明:

$a = "hello";

一个变化变量获得一个变量的值,并将其视该变量的名字。在上面的例子中,“hello”,能够使用变量的名字加上两个$来进行使用,例如。

$$a = "world";

在这一点上,两个变量被定义和存储在PHP的符号树上;$a的内容为“hello”,而$hello的值为“world”。因此如下的申明:

echo "$a ${$a}";

制作了和如下确切相同的输出:

echo "$a $hello";

他们都输出:“hello world”

要在数组中使用变化变量,您必须解决一个含糊的问题。它是:如果您写入了“$$a[1]”,然后解析程序将需要知道您想使用$a[1]作为变量还是使用$$a作为变量,这样索引“[1]”可能就会发生歧义。解决这种歧义的语法如下:“${$a[1]}”或者使用“${$a}[1]”(对上述的第二种情况)。

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