In-depth understanding of the value type and reference type of PHP variables, in-depth understanding of variables

In-depth understanding of the value type and reference type of PHP variables, in-depth understanding of variables_PHP tutorial

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Release： 2016-07-12 09:07:09

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In-depth understanding of the value type and reference type of PHP variables, in-depth understanding of variables

In PHP, most variable types, such as strings and integers , floating point, arrays, etc. are all value types, while classes and objects are reference types. You need to pay attention to this when using them.

I saw netizens discussing PHP’s & symbol. To fully understand its usage, it is necessary to discuss the two forms of variables.

PHP variables are stored in memory like this. The variables do not directly store the content of the value, but the address. For example:

$a = 1;

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It seems to us that the variable $a directly stores the value 1. The actual situation is that the PHP interpreter creates the variable $a, stores the value: 1 somewhere in the memory, and then stores the address of the value in the variable $a.

When you need to get a value, first find the address in variable $a, and then find the value of the variable based on the address.

Look below:

echo $a;

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will output 1, and the PHP interpreter will complete the code like this: find the address stored in $a, find the value stored somewhere in the memory based on the address, and output it to the screen.

It seems like a simple line of code, but the process is like this.

Look further down:

$a = 1;
$b = &$a;

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The variable $b here does an interesting operation. The & symbol takes out the address stored in the $a variable and stores it in the $b variable.

Then, if you use the following code:

echo $b;

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The result will also be output 1. The PHP interpreter first takes out the address stored in $b, and then finds the value based on the address. If we do the following:

$a = 2;
echo $b; //输出2

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You will find that if the value of $a is changed, $b will also change. In fact, conversely, if the value of $b is changed, the value of $a will also change accordingly.

At this point, we can be sure that variables $a and $b store the same address and point to the same value.

Then, we can conclude that they represent the same variable.

To further summarize, it can be concluded that if two variables store the same address, they are the same variable.

After understanding some content, we start to introduce value types and reference types.

Let’s look at the following code first:

$a = 1;
$b = $a;
$a = 2;
echo $b; //输出 1

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Assign the value of $a to $b. After changing the value of $a, the value of $b remains unchanged. That is to say, $a and $b are two different variables pointing to different addresses. This form of assignment that creates different variables is called a value type.

Look again:

class User{
 public $name = ‘Tome‘;
}
$a = new User;
$b = $a;
$a->name = ‘Jim‘;
echo $b->name; //输出 Jim

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Similarly assign the value of $a to $b. After changing $a, $b also changes. That is to say, $a and $b are the same variable and point to the same address. This form of assignment that does not create new variables is called a reference type.