search
HomeBackend DevelopmentPHP TutorialUsage examples of PHP quotation character &_PHP Tutorial

The reference of PHP is to add the & symbol in front of variables, functions, objects, etc. Quoting in PHP means: different names access the same variable content. It is different from the pointer in C language. The pointer in C language stores the address where the content of the variable is stored in the memory.

Variable reference

PHP’s references allow you to use two variables to point to the same content.

<? 
$a="ABC"; 
$b =&$a; 
echo $a;//这里输出:ABC 
echo $b;//这里输出:ABC 
$b="EFG"; 
echo $a;//这里$a的值变为EFG 所以输出EFG 
echo $b;//这里输出EFG 
?> 

Pass-by-reference call of function

I won’t go into details about the call by address. The code is given directly below:

function test(&$a) 
{ 
$a=$a+100; 
} 
$b=1; 
echo $b;//输出1
test($b);   //这里$b传递给函数的其实是$b的变量内容所处的内存地址,通过在函数里改变$a的值 就可以改变$b的值了 
echo "<br />"; 
echo $b;//输出101 

It should be noted that if test(1); is used here, an error will occur. You have to think about the reason yourself.

Function reference returns

Look at the code first:

function &test() 
{ 
static $b=0;//申明一个静态变量 
$b=$b+1; 
echo $b; 
return $b; 
} 
$a=test();//这条语句会输出 $b的值 为1
$a=5; 
$a=test();//这条语句会输出 $b的值 为2 
$a=&test();//这条语句会输出 $b的值 为3 
$a=5; 
$a=test();//这条语句会输出 $b的值 为6 

What $a=test(); gets in this way is not actually a function reference return, which is no different from an ordinary function call. As for the reason: it's a PHP provision. PHP stipulates that what is obtained through $a=&test(); is the reference return of the function. As for what is a reference return (the PHP manual says: Reference return is used when you want to use a function to find which variable the reference should be bound to.)

Using the above example to explain:

Calling a function using $a=test() only assigns the value of the function to $a, and any changes to $a will not affect $b in the function. When calling a function through $a=&test(), its function is to point the memory address of the $b variable in return $b and the memory address of the $a variable to the same place, which produces the equivalent of this effect ( $a=&b;) So changing the value of $a also changes the value of $b, so after executing

$a=&test(); 
$a=5; 

Afterwards, the value of $b becomes 5.

Static variables are used here to let everyone understand the reference return of the function. In fact, the reference return of the function is mostly used in objects.

Object reference

<? 
class a{ 
var $abc="ABC"; 
} 
$b=new a; 
$c=$b; 
echo $b->abc;//这里输出ABC 
echo $c->abc;//这里输出ABC 
$b->abc="DEF"; 
echo $c->abc;//这里输出DEF 
?> 

In PHP5, object copying is achieved through references. In the above column, $b=new a; $c=$b; is actually equivalent to $b=new a; $c=&$b; The default in PHP5 is to call the object by reference, but sometimes you may want to create an object A copy of the original object and hopes that changes to the original object will not affect the copy. For such purposes, PHP defines a special method called __clone.

The role of references: If the program is relatively large, there are many variables that refer to the same object, and you want to manually clear the object after using it, I personally recommend using the "&" method, and then using $var=null to clear it. At other times, use the default method of php5. In addition, for the transfer of large arrays in php5, it is recommended to use the "&" method, after all, it saves memory space.

When you unset a reference, you just break the binding between the variable name and the variable content. This does not mean that the variable contents are destroyed. For example:

<?php 
$a = 1; 
$b =& $a; 
unset ($a); 
?>  

Won’t unset $b, just $a.

When you declare a variable with global $var you actually create a reference to the global variable. That is the same as doing this:

<?php 
$var =& $GLOBALS["var"]; 
?>  

This means that, for example, unset $var will not unset a global variable.

$this In a method of an object, $this is always a reference to the object that calls it.

The pointing (similar to pointer) function of the address in PHP is not implemented by the user himself, but is implemented by the Zend core. The reference in PHP adopts the principle of "copy-on-write", that is, unless a write operation occurs, the pointer Variables or objects at the same address will not be copied.

In layman’s terms, if there is the following code:

$a="ABC"; 
$b=$a; 

In fact, $a and $b point to the same memory address at this time, rather than $a and $b occupying different memories.

If you add the following code to the above code:

$a="EFG";

Since the data in the memory pointed to by $a and $b needs to be rewritten, the Zend core will automatically determine at this time to automatically produce a data copy of $a for $b and re-apply for a piece of memory for storage.

www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/752524.htmlTechArticleThe reference of php is to add symbols in front of variables, functions, objects, etc. Quoting in PHP means: different names access the same variable content. It is different from pointers in C language...
Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
How can you protect against Cross-Site Scripting (XSS) attacks related to sessions?How can you protect against Cross-Site Scripting (XSS) attacks related to sessions?Apr 23, 2025 am 12:16 AM

To protect the application from session-related XSS attacks, the following measures are required: 1. Set the HttpOnly and Secure flags to protect the session cookies. 2. Export codes for all user inputs. 3. Implement content security policy (CSP) to limit script sources. Through these policies, session-related XSS attacks can be effectively protected and user data can be ensured.

How can you optimize PHP session performance?How can you optimize PHP session performance?Apr 23, 2025 am 12:13 AM

Methods to optimize PHP session performance include: 1. Delay session start, 2. Use database to store sessions, 3. Compress session data, 4. Manage session life cycle, and 5. Implement session sharing. These strategies can significantly improve the efficiency of applications in high concurrency environments.

What is the session.gc_maxlifetime configuration setting?What is the session.gc_maxlifetime configuration setting?Apr 23, 2025 am 12:10 AM

Thesession.gc_maxlifetimesettinginPHPdeterminesthelifespanofsessiondata,setinseconds.1)It'sconfiguredinphp.iniorviaini_set().2)Abalanceisneededtoavoidperformanceissuesandunexpectedlogouts.3)PHP'sgarbagecollectionisprobabilistic,influencedbygc_probabi

How do you configure the session name in PHP?How do you configure the session name in PHP?Apr 23, 2025 am 12:08 AM

In PHP, you can use the session_name() function to configure the session name. The specific steps are as follows: 1. Use the session_name() function to set the session name, such as session_name("my_session"). 2. After setting the session name, call session_start() to start the session. Configuring session names can avoid session data conflicts between multiple applications and enhance security, but pay attention to the uniqueness, security, length and setting timing of session names.

How often should you regenerate session IDs?How often should you regenerate session IDs?Apr 23, 2025 am 12:03 AM

The session ID should be regenerated regularly at login, before sensitive operations, and every 30 minutes. 1. Regenerate the session ID when logging in to prevent session fixed attacks. 2. Regenerate before sensitive operations to improve safety. 3. Regular regeneration reduces long-term utilization risks, but the user experience needs to be weighed.

How do you set the session cookie parameters in PHP?How do you set the session cookie parameters in PHP?Apr 22, 2025 pm 05:33 PM

Setting session cookie parameters in PHP can be achieved through the session_set_cookie_params() function. 1) Use this function to set parameters, such as expiration time, path, domain name, security flag, etc.; 2) Call session_start() to make the parameters take effect; 3) Dynamically adjust parameters according to needs, such as user login status; 4) Pay attention to setting secure and httponly flags to improve security.

What is the main purpose of using sessions in PHP?What is the main purpose of using sessions in PHP?Apr 22, 2025 pm 05:25 PM

The main purpose of using sessions in PHP is to maintain the status of the user between different pages. 1) The session is started through the session_start() function, creating a unique session ID and storing it in the user cookie. 2) Session data is saved on the server, allowing data to be passed between different requests, such as login status and shopping cart content.

How can you share sessions across subdomains?How can you share sessions across subdomains?Apr 22, 2025 pm 05:21 PM

How to share a session between subdomains? Implemented by setting session cookies for common domain names. 1. Set the domain of the session cookie to .example.com on the server side. 2. Choose the appropriate session storage method, such as memory, database or distributed cache. 3. Pass the session ID through cookies, and the server retrieves and updates the session data based on the ID.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

ZendStudio 13.5.1 Mac

ZendStudio 13.5.1 Mac

Powerful PHP integrated development environment

mPDF

mPDF

mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

PhpStorm Mac version

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools