Regarding the role of PHP references (that is, adding the ampersand in front of variables, functions, objects, etc.), let’s first look at the following program.
<?php $a = 100; //声明变量a $b = &$a; //声明变量b,引用自变量a echo "$a <br />"; echo "$b <br />"; $a++; //变量a自增1 echo "$a <br />"; echo "$b <br />";//查看变量b,也增加了1,说明使用的是同一存储单元 ?>
Program execution result:
100 100 101 101
Many people misunderstand that references in PHP are the same as pointers in C. In fact, they are not, and they are very different. Except for the pointers in C language that do not need to be explicitly declared during the array transfer process, other points need to be defined using *. However, the pointer to address (similar to a pointer) function in PHP is not implemented by the user himself, but is implemented by the Zend core. Yes, the reference in PHP adopts the principle of "copy-on-write", that is, unless a write operation occurs, variables or objects pointing to the same address will not be copied.
php defaults to passing by value:
<?php $a = 20; $b = $a; $a = $a + 10; echo $a.' and '.$b; ?>
Program execution result:
30 and 20
If you want to pass it as an address, you need to add &, that is:
<?php $a = 20; $b = &$a; $a = $a + 10; echo $a.' and '.$b; ?>
Program execution result:
30 and 30
In other words, & passes the address of $a to $b. In this case, the two variables now share a memory storage area, which means that their values are the same.
The same syntax can be used in functions, which return references, and in the new operator:
<?php $bar =& new fooclass(); $foo =& find_var($bar); ?>
The second thing a reference does is pass a variable by reference. This is accomplished by creating a local variable within the function that references the same content in the calling scope. To put it simply, the parameter of a function is a reference to a local variable. Here’s another example:
<?php function foo(&$val1, $val2) { $val1 += 1; $val2 += 1; } $a=5; $b=10; foo($a,$b); echo $a; echo $b; ?>
To run this code, you pass two parameters to the function, one is a reference to the content of $a, and the other is the value of $b. After executing this function, it is found that the content of $a has changed, while the content of $b is No changes.
The third usage of PHP references is reference return. This usage is a bit difficult to understand. Reference return is used when you want to use a function to find which variable the reference should be bound to. When returning a reference, use this syntax: To put it simply, it is still the return of the reference function. But unlike parameter passing, the & symbol must be used in both function definition and function reference. Here’s an example:
<?php function &find_var ($param) { /* ...code... */ return $found_var; } $foo =& find_var ($bar); $foo->x = 2; ?>
In this example, the assignment to $foo is the return reference of the function find_var, so when assigning a value to $foo->x, the return reference of find_var is assigned instead of a simple assignment.
The last usage of PHP references is reference positioning. There are two main applications: one is global reference. When declaring a variable with global $var, a reference to the global variable is actually established. That is, it is the same as $var =& $GLOBALS["var"];. Another one is the usage of $this. In a method of an object, $this is always a reference to the object that calls it.

PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.

PHP originated in 1994 and was developed by RasmusLerdorf. It was originally used to track website visitors and gradually evolved into a server-side scripting language and was widely used in web development. Python was developed by Guidovan Rossum in the late 1980s and was first released in 1991. It emphasizes code readability and simplicity, and is suitable for scientific computing, data analysis and other fields.

PHP is suitable for web development and rapid prototyping, and Python is suitable for data science and machine learning. 1.PHP is used for dynamic web development, with simple syntax and suitable for rapid development. 2. Python has concise syntax, is suitable for multiple fields, and has a strong library ecosystem.

PHP remains important in the modernization process because it supports a large number of websites and applications and adapts to development needs through frameworks. 1.PHP7 improves performance and introduces new features. 2. Modern frameworks such as Laravel, Symfony and CodeIgniter simplify development and improve code quality. 3. Performance optimization and best practices further improve application efficiency.

PHPhassignificantlyimpactedwebdevelopmentandextendsbeyondit.1)ItpowersmajorplatformslikeWordPressandexcelsindatabaseinteractions.2)PHP'sadaptabilityallowsittoscaleforlargeapplicationsusingframeworkslikeLaravel.3)Beyondweb,PHPisusedincommand-linescrip

PHP type prompts to improve code quality and readability. 1) Scalar type tips: Since PHP7.0, basic data types are allowed to be specified in function parameters, such as int, float, etc. 2) Return type prompt: Ensure the consistency of the function return value type. 3) Union type prompt: Since PHP8.0, multiple types are allowed to be specified in function parameters or return values. 4) Nullable type prompt: Allows to include null values and handle functions that may return null values.

In PHP, use the clone keyword to create a copy of the object and customize the cloning behavior through the \_\_clone magic method. 1. Use the clone keyword to make a shallow copy, cloning the object's properties but not the object's properties. 2. The \_\_clone method can deeply copy nested objects to avoid shallow copying problems. 3. Pay attention to avoid circular references and performance problems in cloning, and optimize cloning operations to improve efficiency.

PHP is suitable for web development and content management systems, and Python is suitable for data science, machine learning and automation scripts. 1.PHP performs well in building fast and scalable websites and applications and is commonly used in CMS such as WordPress. 2. Python has performed outstandingly in the fields of data science and machine learning, with rich libraries such as NumPy and TensorFlow.


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