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HomeBackend DevelopmentPHP Tutorial 【转】php函数摘引

【转】php函数引用

转载自?hosserer
最终编辑?hosserer

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一个形象的比喻:

引用:你是我的影子,我穿什么衣服你也是什么衣服,你被unset了,我依然是我。

传值:你是我某个时刻的一张照片,或者说你是一个独立的东西,我说你是苹果,你就是苹果,跟我没有关系了。

以下为转载:

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php函数前面加&符号的意思是函数的引用返回,php函数前面加&符号有什么作用呢

Php代码?

function &test()
{
static $b=0;//申明一个静态变量
$b=$b+1;
echo $b;
return $b;
}

$a=test();//这条语句会输出 $b的值 为1
$a=5;
$a=test();//这条语句会输出 $b的值 为2
$a=&test();//这条语句会输出 $b的值 为3
$a=5;
$a=test();//这条语句会输出 $b的值 为6?
下面解释下: 
通过这种方式$a=test();得到的其实不是函数的引用返回,这跟普通的函数调用没有区别.

至于原因: 这是PHP的规定
php规定通过$a=&test(); 方式得到的才是函数的引用返回.

至于什么是引用返回呢(PHP手册上说:引用返回用在当想用函数找到引用应该被绑定在哪一个变量上面时。)

用上面的例子来解释就是
$a=test()方式调用函数,只是将函数的值赋给$a而已, 而$a做任何改变 都不会影响到函数中的$b.
而通过$a=&test()方式调用函数呢, 他的作用是将return $b中的 $b变量的内存地址与$a变量的内存地址,
指向了同一个地方. 即产生了相当于这样的效果($a=&b;) 所以改变$a的值,也同时改变了$b 的值 ,所以在执行了:
$a=&test(); $a=5; 以后,$b的值变为了5 ......


php变量前面加&符号是什么意思

先看一个示例

Php代码?
$foo = 321;???
$bar = &$foo;????
$bar = 123;???
print $foo;

$foo = 321;
$bar = &$foo;?
$bar = 123;
print $foo;那么输出的结果将会是什么呢

Php代码?
123????

为什么会这样呢?

改动新的变量将影响到原始变量,这种赋值操作更加快速
注意:只有命名变量才可以传地址赋值
就是说,改变了$bar的值,也就改变了$foo的值了

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