Assignment of PHP variables: the difference between passing by value and passing by reference

Variable refers to the amount that the value can change during the execution of the program. It is used to save a value so that we can call it conveniently. However, there are two ways to assign values ​​to variables in PHP: value transfer and reference transfer. This The two methods of assigning values ​​​​to variables are different. In this chapter, we will lead you to understand: The difference between value transfer and reference transfer

First, let’s take a look at value transfer :

The value transfer method is the most commonly used method and the default method to assign values ​​to variables. Let’s use an example to illustrate:

<?
header("content-type:text/html;charset=utf-8");     //设置编码
echo "值传递的方式";
echo "<hr/>";
$var1= "PHP";
$var2=$var1;
echo $var1."<hr/>";
echo $var2;
?>

Code running results:

From the above example, we can see that value transfer is to transfer the value of the current variable Giving another variable is equivalent to a copy operation. The two variables are independent of each other. If we change the value of one variable, the value of the other will not change. See the example below

<?
header("content-type:text/html;charset=utf-8");     //设置编码
echo "值传递的方式";
echo "<hr/>";
$var1= "PHP";
$var2=$var1;
echo $var1."<hr/>";
echo $var2."<hr/>";

echo "<p>改变其中一个变量的值,另一个不会有变化</p>";
$var2="HTML";

echo $var1."<hr/>";
echo $var2."<hr/>";
?>

Code running results:

Let’s take a look at reference transfer

Reference assignment uses “&” to represent a reference. Using reference assignment If you change the value of one variable, the other will also change.

Example

<?
header("content-type:text/html;charset=utf-8");     //设置编码
echo "引用传递的方式";
echo "<hr/>";
$var1= "PHP中文网";
$var2=&$var1;
echo $var1."<br/>";
echo $var2."<br/>";
?>

Code running results:

There is no change in the two variables at this time, but if we change one of them What’s the value?

<?
header("content-type:text/html;charset=utf-8");     //设置编码
echo "引用传递的方式";
echo "<hr/>";
$var1= "PHP中文网";
$var2=&$var1;
echo $var1."<br/>";
echo $var2."<br/>";

echo "<p>使用引用传递的方式改变其中一个变量的值</p>";
$var2="HTML";

echo $var1."<br/>";
echo $var2."<br/>";
?>

Code running results:

#Use reference passing method to assign values ​​to variables. If the value of one variable is changed, the other variable will also change. .

Summary

Through some of the above examples, we can conclude that The difference between value passing and reference passing is: Value passing copies the content of the original variable. Then use a new memory space to save it. The two variables are independent of each other, and passing by reference is equivalent to giving the current variable an alias. In fact, the two variables refer to the same value. It is equivalent to giving a variable two names

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