Explanation of passing by value and reference in php

This article mainly shares with you the explanation of value transfer and reference in PHP. It is mainly shared with you in the form of text. I hope it can help everyone.

Introduction:

Each php variable exists in a variable container called "zval". A zval variable container, in addition to containing the type and value of the variable, also includes two bytes of additional information. The first one is "is_ref", which is a bool value, used to identify whether this variable belongs to the reference set(referenceset). Through this byte, the PHP engine can distinguish ordinary variables from reference variables. Since PHP allows users to use custom references by using &, there is also an internal reference counting mechanism in the zval variable container, to Optimize memory usage. The second byte is "refcount", which is used to indicate the number of variables (also called symbols) that points to the zval variable container. When the value of "refcount" is 1, the value of "is_ref" is always FALSE.

Example:

<?php$a = 10;
//将常量值赋给变量，会为a分配内存空间$b = $a;
//变量赋值给变量，给b分配了内存空间，并将a变量的类型和值复制一份存储到b的存储空间 $c = &$a;
//引用是不会为c分配空间的，c和a是共用一份内存空间数据。

When assigning a variable to a new variable in PHP, memory space will not be allocated immediately for the new variable, but a reference to the memory space will be added. When any changes are made to the original variable or the new variable, a memory space will be allocated for the new variable.

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