The difference between passing by value and passing by reference in php

php value transfer: within the function scope, changing the variable value will not affect the variable value outside the function.

PHP By reference: Within the function scope, any changes to the value are also reflected outside the function, because the memory address is passed by reference.

Pass value: is the same as copy. [For example, I have a house. I give you building materials. You build a house that is exactly the same as mine. Whatever you do in your house will not affect me. What I do in my house will not affect me. Nothing will affect you, independent of each other. 】 (Recommended learning: PHP video tutorial)

<?php    
$testa=1;               //定义变量a 
$testb=2;               //定义变量b    
$testb = $testa;       //变量a赋值给变量b    
echo $testb;            //显示为1    
?>

Passing reference: It is similar to the pointer of C language, and it feels almost the same. For example, I have a house. If I give you a key, both of us can enter the house. Whatever you do in the house will affect me.

<?php    
$param2=1;               //定义变量2    
$param1 = &$param2;      //将变量2的引用传给变量1    
echo $param2;            //显示为1    
$param1 = 2;             //把2赋值给变量1    
echo $param2;            //显示为2    
?>

Advantages and Disadvantages: Passing values ​​will be time-consuming, especially for large strings and objects, this will be a very expensive operation, transferring references, functions Any operation within is equivalent to the operation of the transferred variable, and it is efficient when transferring large variables!

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