Infinite classification of recursive functions

function fun($pid=0,&$brr=array()){//Why does it not work if you remove &?

<code>$sql="select * from wuxianji where pid=$pid";
$rs=mysql_query($sql);

while($arr=mysql_fetch_assoc($rs)){
    $brr[]=$arr;
    fun($pid=$arr['id'],$brr);
}
return $brr;</code>

}
$brr=fun();
echo '

';print_r($brr);
die();

//What does &$brr=array() & in function parameter passing mean? what's the effect? 

                            
                        


                                                                                                                        
                     
Reply content:
                      
                                                            
function fun($pid=0,&$brr=array()){//Why does it not work if you remove &? 
<code>$sql="select * from wuxianji where pid=$pid";
$rs=mysql_query($sql);

while($arr=mysql_fetch_assoc($rs)){
    $brr[]=$arr;
    fun($pid=$arr['id'],$brr);
}
return $brr;</code>
Copy after login
Copy after login
}
$brr=fun();
echo '
';print_r($brr);<br>die();</p>
<p>//What does &$brr=array() & in function parameter passing mean? what's the effect? </p>

                            
                        
            <p class="answer fmt" data-id="1020000006752366">
                                    </p>
<p>Look at the examples in the manual and you will understand&</p>
                            
            <p class="answer fmt" data-id="1020000006752469">
                                    
</p>
<p>Because & is a reference, when the & symbol is used, the modifications you make to the parameters in the function will also be carried outside the function. Without the & symbol, the modification of parameters you face in the function ends when the function ends. </p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false"><code>function a1($a) {
    $a = 20;
}
function a2(&$a) {
    $a = 20;
}
$a = 10;
a1($a);
var_dump($a);
a2($a);
var_dump($a);</code>
Copy after login