What is the difference between passing by value and passing by reference in php

The difference between passing by value and passing by reference in php is: for passing by value, changing the size of the variable value within the function scope will not affect the variable value outside the function; for passing by reference, within the scope of the function, the size of the variable value will not be affected. Any changes to the value are reflected outside the function, and the memory address is passed by reference.

Difference analysis:

php value passing: If the size of the variable value is changed within the scope of the function, it will not affect to the variable value outside the function.

PHP pass-by-reference: Within the function scope, any changes to the value are reflected outside the function, because the pass-by-reference passes the memory address.

Example analysis:

Passing 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, they are independent of each other.

<?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 in 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
?>

Passing values ​​will be time-consuming, especially for large strings and objects. This will be a very expensive operation. Transferring references, any operation within the function is equivalent to transferring variables. The operation is efficient when transferring large variables!

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